Signey
Thu, Jun-24-04, 18:22
I found this and thought it might be of interest. More as a reference piece than anything else. It's really everthing you
ever wanted to know about oil but were afraid to ask. :lol:
Cheers!
Signey
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All About Oils
From The Consumer's Guide to Using Oils for Flavor & Health
Vegetable oils are not all alike.
Some oils have more flavor. Some provide essential nutrients. Some hold up better to high heat or long storage. Some contain no pesticide residues.
Do you know which oil is which?
This document provides you quick, factual answers so that you can use each type of oil to its best advantage.
Proper packaging by the manufacturer and careful storage at home are both important to preserve nutrients and prevent rancidity in oils.
Heat, oxygen, and light are the most common damaging elements for vegetable oils. The more natural an oil, the more protection it needs. Oils properly sealed in glass containers, without oxygen trapped at the top (oxygen initiates deterioration), are quite stable until opened. Breaking the seal allows atmospheric oxygen to begin breaking down the oil. You can slow this process dramatically by refrigerating your oils once you've opened them.
Light can damage unrefined oils by reacting with chlorophyll and other bioactive components in the oil. Light-induced deterioration combined with oxidation can rapidly affect the status of vitamin E, carotene (vitamin A precursors), and other nutritive components of an oil. So, even if an attractive label tempts you to keep a bottle of oil on the counter, remember that it's best to keep the oil in the dark. Refined oils, however, are far less susceptible to light-induced damage.
Storage Guide
To safeguard the nutritive value and longevity of your oils, keep them in a cool 40F to 72F, dark cupboard until opening, and then store them in your refrigerator. Storage under these conditions provides a shelf life of 10-14 months for unrefined oils, and 14-20 months for refined oils. Freezing can extend an oil's shelf life. Again, refrigeration is not required but does improve shelf life.
Some Oils Are Environmentally Sound
Oils labeled "organic" are those pressed from seeds, nuts, or beans grown without the use of commercial pesticides, fungicides, fertilizer, or herbicides, and produced through cold-pressing or expeller-pressing processes. By consuming organic foods you minimize your intake of non-natural chemicals and help support the health of the environment.
Organic Guide
Any food that claims "organic" should bear a seal of certification from an independent third-party organization, such as the Organic Growers and Buyers Association. This seal assures quality, care, and commitment.
Some Oils Have Good Taste
The most flavorful oils are those left unrefined. Unrefined oils contain a number of biochemical compounds that provide flavor, scent, color, and nutrients. These compounds also reduce an oil's shelf-life stability. Unrefined oils are therefore the most flavorful, nutritious and the most sensitive to storage.
The refining process removes an oil's natural, bioactive compounds to achieve a uniform, neutral, stable product. Refined oils are therefore odorless and bland.
Why not always choose flavorful, unrefined oils? The answer depends on what you're cooking. Unrefined oils are more reactive to heat; in fact, they smoke and foam when used for frying or at temperatures above 375F. They also have a slightly higher moisture content, which makes them pop and fizz at medium to high temperatures. Refined oils, however, are stable at even high temperatures. The deep frying or other high-heat cooking, refined oils are the best choice.
Basic Facts on Fats and Oils
What Are Fats and Oils?
The word "fats" names a food group that includes what you probably think of as both fats and oils. Fats come from animal and plant Supplies and are usually solid at room temperature; oils are produced mainly from plants, and are liquid. The most common oils are extracted from seeds (safflower, sunflower, sesame, canola, flax), beans (peanuts, soy), grains (corn, wheat germ), fruits (avocado, olive), and nuts (almond, coconut, walnut, palm kernel).
Fats and oils are alike in that they're both made up of fatty acid molecules. You may already know the four basic types: saturated, monounsaturated, polyunsaturated, and superunsaturated. Because these fatty acids differ in their molecular structure, they differ in their behavior in your kitchen and in your body.
Saturated fatty acid molecules are shaped like a straight line, so they easily stack together into a compact mass. This dense form resist change, even when subjected to stresses such as air, heat, or light. For instance, a saturated fat is one that stays hard at room temperature and is slow to spoil (become rancid) butter and coconut oil are good examples.
Monounsaturated fatty acids have a single "kink" in their molecular strand. This kink makes them more fluid and more reactive than the unsaturated fats. Olive and canola oils are rich in monounsaturated fatty acids; you may have noticed that these oils get thick when you refrigerate them but they return to fluidity at room temperature.
Polyunsaturated fatty acids have two kinks, which makes them even more reactive molecules. Safflower and corn oils are well-known polyunsaturated oils. Both deserve careful handling to prevent rancidity.
The superunsaturated fatty acids are molecules with three kinks. These fats are rare and carry the most essential fatty acid nutrients. They are found mostly in fish tissue and in the seeds of the black currant, evening primrose, and flax plants. Superunsaturated oils are fluid at even very cold temperatures and react "firecracker" fast with oxygen. They must be carefully protected to preserve their nutritive qualities.
What Is a Cold-Pressed Oil?
Vegetable oils are generally produced through one of three processes: solvent extraction, mechanical (expeller) pressing, or cold pressing. Once produced, an oil can be left unrefined or can be put through a multi-step refining procedure.
Most mass market oils are obtained by solvent extraction, which involves the use of chemical solvents (some carcinogenic). They are also usually refined, a process during which temperatures can exceed 500F.
Mechanically (expeller) pressed oils are produced through a chemical-free, continuous mechanical process in which friction can generate temperatures of up to 185F. Refining removes a variety of naturally occurring materials to produce an oil that can withstand high heat without burning or releasing undesirable byproducts.
Cold-pressed oils are produced by a mechanical batchpressing process in which heat-producing friction is minimized so that temperatures remain below 120 F. The term cold-pressed, however, is frequently misapplied. True cold pressing involves the use of hydraulic presses or refrigerated in-line cooling devices on expeller presses.
What's the importance of heat in processing?
Heat is particularly influential in oil production because each 10 degree increase in temperature dramatically raises the rate at which the fatty acids react with oxygen, potentially destroying nutrients and promoting spoilage. Even after processing, heat is important because oils can be damaged if they are stored at warm/high temperatures.
Do Oils Go Rancid?
Oils spoil (become rancid) after prolonged contact with air (oxygen), light, and/or heat. You can identify a rancid unrefined oil by its unusually strong odor and sharp or bitter flavor. The off-odors are gases produced by the reactive fatty acid molecules; it's nature's way of letting you know the oil is past its prime.
Spoilage in refined oils is harder to detect because these oils have had their flavor and odor bodies removed. This makes refined oils far less susceptible to damage from light, heat, or oxygen exposure. Although their shelf-life is long (usually 24-30 months), deterioration can occur. Certainly, if you notice an unpleasant odor or flavor in refined oil, it's a sign of rancidity.
To protect your oils from spoilage, store them in a cool, dry place, out of harsh light. Alternatively, keep the oils you use daily in the refrigerator (note that to dissolve the solids in cold, unrefined oils you can just set the bottle in a bowl of warm tap water). Freezing is a good way to extend shelf life, especially with the super-reactive supplement oils (canola, flax, wheat germ) sold in plastic containers. Be careful, however, if you store glass bottles in the freezer, because the glass will become fragile.
It's also wise to purchase oils in small-sized bottles, because fresher oils are healthier oils.
OIL TERMINOLOGY IN THE NATURAL FOOD INDUSTRY
Listed below are some basic terms and definitions for natural oils and their processing.
Active Oxygen Method
Active oxygen method is an accelerated rancidity test in which the fat/lipids to be tested are held at a constant elevated temperature while air is bubbled upward through the hot fat/oil. Active oxygen stability (A.O.M.) is expressed as the number of hours of heating until a peroxide value (PV) of 100 milli-equivalent units has been reached. When reaching the level of PV=100, the oil has been determined to be fully rancid and not fit for human consumption.
Antioxidant
An antioxidant is any naturally occurring or manufactured material whose addition into a fat/lipid product provides increased oxidative stability. Antioxidants decrease oxidative stress by limiting chemical reactions and the uptake of single oxygen molecules from the atmosphere. Antioxidants interfere with the uptake of free oxygen from the atmosphere. Some oils already have high, naturally occurring antioxidants such as vitamin E, alpha, beta, gamma and delta tocopherols, sesamin, and sesamol. Natural oil soluble antioxidants, such as rosemary oil, vitamin E, (i.e., alpha-tocopherol) and other fat soluble compounds are occasionally added as antioxidant adjuncts to slow down the deterioration of vegetable oil and increase shelf life. All antioxidants must be US F.D.A. & US Department of Agriculture approved. Antioxidants which are synthetic are not regarded as natural adjuncts and therefore can not be included as ingredients of natural or organic oils.
Bleaching
Bleaching is the treatment of a fat or oil with activated carbon, diatomaceous earth, non-acidified and acidified clays, or any agent that removes color bodies and some odors from the fat or oil. Bleaching involves the mechanical straining of unrefined oils through plate and frame filters through a filter medium of bleaching clays and earth. The bleaching process uses paper or cloth filters which removes suspended compounds and delivers a more uniform lighter colored oil.
Canola Oil (Low Erucic Acid Rapeseed/LEAR) Canola oils pedigree originates from the brassica campestris family, or common mustard plant. It is a type of rapeseed originally bred in Canada, hence the name Canada oil or canola for short. It is high in monounsaturates, low in saturates and usually fully refined for use as a culinary oil. It has high levels of essential fatty acids (EFAs). It has 10% alpha-linolenic acid (Omega-3), which is a rare fatty acid in culinary oils. The erucic acid content in canola oil has been bred out. To be classed as a LEAR oil, the acid content of erucic has to be less than 2% of total fat. In most instances it is less than 1% in natural oil products and new breeding programs are lowering that value to less than 0.5% of total fat.
Cold Pressed/Processed Oil
For a number of years the term cold pressed has been erroneously used to describe oil removal using expeller pressed methods. The term has even been applied to refined oils (which expose oils to high temperatures from 243 to 470F during the refining process). Obviously this is a misnomer to the consumer who assumes cold pressing involves low temperature processing throughout. True cold pressing is legally defined in Europe as oil extraction at temperatures below 50C or 122F, and only to fully unrefined oils. True cold pressing occurs in:
1. The ancient method of stone grinding or milling, as in the crushing of olive oils
2. Bladder press extraction, which uses simple compression for fruit oils such as olive or avocado
3. Hydraulic presses, which uses simple compression
4. Low resistance expeller pressing, which controls screw worm, drive speeds and feed rates levels to temperatures which do not exceed 122F.
5. Modified Atmospheric Crushing (MAC) and Modified Atmospheric Packing (MAP), which employ enhanced cooling and refrigeration techniques using modified vegetable oil expeller presses that meet cold pressing temperature standards
MAC and MAP processing employs modified expeller presses. However, these presses are designed with in- line cooling devices to insure oils are kept below the temperatures called for in cold pressed oils. Proprietary engineering modifications make it possible to produce cold pressed oils using techniques that are more sophisticated, yet effective or even better than the older technology of simple mechanical cold pressing delivering superior nutritional oils.
Crude or Integrated Vegetable Oil
Typically solvent-extracted oil is blended with the first pressing of oil from a pre-pressed type expeller unit, which partially defats the meal. Pre-pressing leaves as much as half the oil in the seed. The rest is removed by solvents. The technique of blending pre-pressed expeller and solvent extracted oils is called integrated oil. The finished solvent/pre-pressed oils, when blended, are then sent off as crude oil for further refining. Basically, expeller pressing leaves about 5 to 13% of oil residual in the meal. Solvent processing leaves only 1 to 3% residual oil in the meal making it a more efficient processing method, yet a less healthy product. Solvents tend to concentrate in the meal. The meal is sold as animal feed. Excessive amounts of solvent in meal causes anemia in livestock. Hexane compounds are carcinogens according to the Environmental Protection Agency (E.P.A) and are classed as a hazardous substance. Hexane also poses a serious environmental threat as it is a hydrocarbon polluter and produces ozone and air pollution when it is vented into the atmosphere during the flash off cycle.
Crude is the term oil technicians use for either integrated unrefined vegetable oils or 100% solvent extracted oil before it moves on to be refined. Since it is at least a blend of expeller and solvent extracted oils, it is a misnomer to refer solely to expeller pressed unrefined oil as crude. Crude is a reference that only refers to large scale industrial extraction. It does not refer to unrefined oils that are processed at the cottage or intermediate industry level or for natural oils which employ greater standards of care and protection. Standard commercial extraction takes no additional precautions for sanitation, oxidation or high temperature protection. According to the USDA, crude oils are not considered fit for human consumption until they have been refined and impurities removed. The attitude in large scale refining operations is that the deterioration of the oil can be cleaned up through extensive refining.
Deoderizers
Deodorization of fats and oils removes reacted compounds which are decayed byproducts in the form of peroxidized fats. The process uses high vacuum, temperature, and live steam to remove strong flavors and odors from the fat or oil. Temperatures used in a deodorizing steam column are upwards to 200C or 450F. Lower temperatures (120C or 280F) are possible but longer exposure times are needed in the steam column to effectively remove impurities.
Essential Fatty Acids (EFAs)
Essential fatty acids (EFAs) are two fats that the human body cannot synthesize from other organic compounds or foods and are essential for life. They are Omega-6 (linoleic acid) and Omega-3 (alpha-linolenic acid). These acids are found abundantly in many vegetable oils. Both are classed as polyunsaturated fats. However, the alpha- linolenic acid (Omega-3 fraction) is also regarded as a super polyunsaturate. Proper handling and storage protection is needed as both fatty acids deteriorate rapidly in the presence of heat, light and oxygen.
Expeller Pressed
An expeller press is a screw type machine which presses oil through a caged barrel-like-cavity, using friction and continuous pressure from screw drives to move and compress the seed material. The oil spent (defatted) fiber is formed into a hardened cake which is released from the machine with the previously removed oil seeping through metal barrel slates that have small spacings to allow the oil to pass through without any seed fiber solids. Pressure involved in expeller pressing creates heat in the range of 60 - 99C or 140 - 210F).
Vegetable oils in the natural foods/health foods industry are almost all of the expeller pressed type. Expeller oil pressing is a mechanical rather than chemical extraction process. This method results in no solvents (such as hexane or other petroleum based distillents) residues left in the oil. It is the critical quality difference between refined oils often found in the natural foods marketplace as opposed to mass market or super market brands.
Fats and Oils
Fats and oils are called lipids which is their scientific name. Molecularly, they are long strings of carbon molecules which form triglycerides (or three fatty acid molecules tied to a glyceride molecule). Some have mono and diglyceride molecules which are one or two glyceride compounds. Fats and oils are a combination of one unit glyceride and three units fatty acids. Fat is normally semi-solid or solid at room temperature whereas an oil is normally liquid at room temperature. There are many types of fats and oils in nature. There are approximately 45 fatty acids fractions which make up fats.
Fatty Acid Profile
Fatty acids are formed through differing carbon chain lengths with either single, double, or triple bonds. Each oil has a different complex of fatty acids, which when broken down, identify its chemical signature. The four subgroups of fatty acids are the saturated, monounsaturated, polyunsaturated and super unsaturated fatty acids. Each group is characterized by increasing reactivity to heat, oxygen, and light energy. The longer the fatty acid chain the greater the instability and reactivity to oxygen, heat, and light energy. Saturated fat, with the shortest carbon chain length, is the most stable and least prone to oxidation. The super unsaturated oils are the longest chains of fats which have the least stability and shortest shelf life. On the other hand, the greater the reactivity to oxygen, heat, and light energy, the greater the use of the fatty acid as a nutritional supplement due to the hormone- like properties of these highly dense lipids.
Flavor
Flavors are indicative of an oil's value in its various commercial and food applications. Oils offer rich flavor bearing properties, provide texture, and enhance and compliment other flavors in foods. Describing oils by taste sensation involves highly subjective discriminations. Flavor variations may be described as bland, neutral, nutty, tallowy, fruity, or rancid. The properties associated with oils range from light to heavy, sweet to bitter, and fresh to rancid.
Free Fatty Acid (FFA)
Free fatty acid is the amount of fatty acid occurring naturally or produced as a byproduct in fat processing. Free fatty acids exist in an uncombined state as a definable chemical unit. This unit value is normally expressed as the breakdown of oleic acid. Free fatty acids are expressed as percent acidity calculated as oleic acid (a monounsaturated fat). The uncombined fatty acid comes from the breakdown of fat (as triglycerides) into a unit of fatty acid and glyceride.
First Pressing
Generally, there is only one pressing for vegetable oils, so first pressing is a meaningless term other than for olive oil. Second pressing usually involves the use of solvents for most other vegetable oils and therefore the term is misused when applied to oils other than olive.
High Oleic Oils
High oleic varieties are oil hybrids that have been genetically enhanced through selective plant breeding to produce high ratios of oleic acid (omega-9 fraction). The rise in oleic acid increases the oils stability and shelf life. High oleic oils have been bred to reduce polyunsaturated components and increase the monounsaturated content. High oleic oils should have at least 90% of the oleic content similar to olive oil. Olive oil is the benchmark for good culinary oleic based oils. This means that an oil should be at least 75% oleic by total fat content to be regarded as high oleic. High oleic oils perform well in medium to high heat cooking applications, such as deep frying or high heat sauteing.
Hydrogenated Fat and Oil
Hydrogenated fats are oils that have been processed through a chemical hardening method to achieve increased plasticity (stiffness) of the liquid oils at room temperature. Partial hydrogenation (brush hydrogenation) hardens oils but does not make them fully solid. Full hydrogenation requires complete conversion of a liquid oil into a solid fat at room temperature (72F). A fully hydrogenated oil has natural saturated fats left intact and all the remaining mono and polyunsaturated fatty acids become converted from their fluid cis-configuration to a full trans- fat rigid configuration. (See Trans Fatty Acids or Trans-Fats).
Hydrogenation Process
The hydrogenation process employs 1) high heat, 2) a metal catalyst such as nickel, zinc, copper, or other reactive metals, and 3) hydrogen gas. The metals are used to react with the hydrogen gas which is bubbled up through the mixture. The metals catalyze the hydrogen and carbon atoms and converts the cis-configured fatty acids by flipping one of the attached hydrogen molecules and rotating it half the diameter of the carbon chain. This effectively creates a new molecular shape resulting in a stiffer or more rigid material, hence the change from a liquid to a semi-solid or solid substance. This new shape stiffens with the hydrogenation process making the oil behave more like a saturated fat (such as coconut fat which is 92% saturation and solid at room temperature). Trans-fats are the result of this reaction. Partial hydrogenation or brush hydrogenation is a minimal conversion step which only offers a small degree of reaction by hydrogenation. Brush hydrogenation increases stability for volatile fatty acids like the Omega-3 (alpha-linolenic) and Omega-6 (linoleic) polyunsaturated oils. Most commercial salad dressing oils, such as soybean oil, have been brush hydrogenated. Hydrogenation raises the melting point of the fat and retards rancidity. But as recent health studies have found, other problems can ensue when consuming large amounts of trans fats from hydrogenated products.
Hydrolysis
A chemical reaction involving molecular breakdown by the reaction of an ester with water forming an acid and alcohol. It is a reaction between a fat or oil and water in the presence of various alkali agents, acids, metals lipase, or molds, which form new fatty acids and glyceride compounds. This reaction usually occurs under high temperatures and pressures. Hydrolysis also occurs when high degrees of moisture are naturally present in an oil. Over time, the vegetable oil will breakdown as a consequence of the hydrolytic action taking place between the fatty acids and the water content in the oil.
Iodine Value (IV)
Iodine values are used as signature markers for differing species or varieties of vegetable oils. Each oil has a specific iodine level and this ratio does not alter within the species. When oils are co-mingled with other species (i.e. canola and sesame oil) the iodine levels will be a value averaging between the normal iodine ranges typically found in each oil. This indicates that the oil is no longer a pure vegetable oil of one species, and some mixing has occurred to alter the iodine value. Iodine values are used to determine if tampering of oils has occurred.
Iodine value is an expression of the degree of unsaturation of a fat. It is measured by the amount of iodine which will react with a natural or processed fat under prescribed conditions. The iodine reacts with the chemically unsaturated hydrogen short group and is indicative of the degree of hydrogenation. When unsaturation is reduced, iodine values are lowered by hydrogenation. The iodine value is expressed as centigrams of iodine per gram of oil.
Isoelectric Dispersion Technology (IDT) (non-hydrogenated fats)
This is a licensed, patent-pending technology that converts a liquid fat into semi solid or solid fat at room temperature through a dispersion method which employs oil soluble thickening agents. The process breaks down fats to submolecular units with a very high degree of particulate dispersion. The IDT method avoids destructive use of high heat and caustic agents and provides a spreadable product without being hydrogenated. IDT methods are safer, healthier and gentler than traditional hydrogenation.
Modified Atmospheric Crushing and Modified Atmospheric Packing (MAC & MAP)
This is a class of processing which excludes light, heat, oxygen, and reactive metals in the presence of oils (used for nutritional supplements oils). Modified atmospheric packing (MAP) involves comprehensive refrigeration of oils during crushing, processing, settling, and filling of specifically designed bottles. This class of oil processing aims at employing as benign an extraction method as possible to keep nutrients and freshness intact. Temperatures do not exceed cold pressing ranges (less than 50C or 122F. The same care is employed in the bottle filling process which keeps the destructive influences of light, oxygen, heat, and reactive metals away from the oil. Encapsulated and bottled MAP products are stored and transported in inert, light proof materials, and kept refrigerated.
Oxidation
A chemical reaction involving the combination of single oxygen molecules randomly drawn from the atmosphere and combined with a reactive triglyceride molecule. Spoilage usually results from oxidative stress in foods. In oils, rancidity results in the formation of peroxides as a consequence of the free radical phenomena. Peroxidized levels past 100 megs/per kg. Are declared rancid by Department of Agriculture standards, and are a fraction of that level in supplement oils (usually not exceeding 5.0 PV in super unsaturated fatty acids). On the other hand, olive oil, which is deemed marketable at a starting PV of 20 experience high levels of peroxide formation and still can be considered safe and edible. Prior to being at a PV level of 20, the oil is considered immature and green. Peroxide values vary dramatically with different types of oil. The oil's intrinsic stability properties determine what the safety levels are. Sesame contains sesamin and sesamol, two very strong inhibitors which keep this oil naturally stable for very long periods of time. It is impossible to apply one standard for all oils as oils have very different properties, with different natural compounds that affect stability, taste and utility. Each oil has to be measured and tested on its own merits.
Peroxide Number (PV)
Peroxide value is a measure of the extent of oxidative absorption and entrainment of oxygen in a fat or oil. To properly interpret PV's, the age and handling history of the fat or oil must be known as peroxide values rise and fall on a bell curve with absorption and remission of oxidative levels in the oil, depending on the age of the oil. High peroxide usually indicates high degree of oxygen absorption. This value coupled with high free fatty acid (FFA) values indicates increased rancidity. If the value starts low, goes high and drops, and the second benchmark value continues to increase, the oil has become or is fully rancid and inedible. Peroxides can be lowered by reaction to bleaching, deodorization and alkali refining steps.
Photon Decay
Light is a form of energy and imparts chemical reactions in oils. Unrefined oils are more light sensitive as the chromaphores (color bodies) convert light/oxygen into free radicals through chlorophyll synthesis which is still active in the unrefined oil. This action continues to create lipase reactions and the ensuing breakdown product creates off flavors. Ketones, aldehydes and acetones are breakdown products producing off flavors in vegetable oils. The free radical process is most identified with light or photon decay and oxygen. Free radical formation is present throughout the process of decay and occurs as either alpha or beta types of oxidation. Alpha oxidation is oxygen drawn from the atmosphere, beta oxidation occurs from the entrained oxygen that is systematically present and produces reactions in the oil even while completely protected from outside influences such as heat, light and atmospheric oxygen. Long chained essential fatty acids are especially prone to light sensitivity and heat damage. Fully refined oils do not have the same potential because the trigger mechanisms of the chromaphores (color bodies) have been removed. Increasing free radical synthesis occurs with natural pigments in the oil. Refined oils have few or none and therefore have a much longer shelf life as compared to an unrefined pigment rich oil.
Rancidity
Rancidity is characterized by the development of off flavors, odors and colors. Rancidity in oils will usually result in a gag reflex if consumed by humans. Rancid oils have a bitter, high acrid after-taste which is easy to distinguish. Oxidative and hydrolytic stress also breakdown oils and speeds rancidity. Rancidity is measured as PV 100 meg/kg of sample tested.
Refining
Refining involves the removal of reacted compounds and decay compounds in the form of peroxidized fats and free fatty acids. Alkali refining employs a strong base, such as caustic soda, to consume the high acid content of reacted fats and bring the vegetable oil into American Oil Chemists Society standards (AOCS specification) and trading rules of the National Institute Of Oil Processors (NIOP). Most oils are sought to have peroxides brought back to a level of less than .05 megs/per kg. in a fully refined or purified vegetable oil. The follow-through steps of refining are:
1. Alkali refining, (to remove peroxides and impurities)
2. Centrifuging (to remove moisture and reacted fats, water washing)
3. A second centrifuging operation and finishing/polishing (in preparation for additional steps of deodorizing)
1. Bleaching (to remove color bodies)
2. Deodorizing (to remove odors and aromas)
3. Winterizing (to remove phospholipid, stearins, waxes and other compounds which crystallize in cold temperatures)
The description of full refining is R-B-D-W, which stands for the four steps of refining, bleaching, deodorizing, and winterizing. Not all refined oils are processed with all the steps. Organic refined oils use only natural agents such as citric acid and diatomaceous earth.
Reversion (flavor)
Reversion is a reversal of flavor properties where unfavorable off-flavors occur in an oil long after it has been refined. Off-flavors develop because polyunsaturated fats, particularly the Omega 3's, continue a rapid decline as they attract and absorb oxygen. Soybean and canola oil are subject to strong flavor reversion when improperly handled and under poor storage conditions. High storage temperatures, poor seals, or leaking bottles all invite quality deterioration.
Solvent Extraction
Solvent extraction is achieved through the desiccation or grinding of seed. The seed is then purged or washed with a petroleum distillate (such as hexane) to release the fat in the seed. The solvent is flashed off through heat in a sealed chamber. The oil/solvent blend is heated to 100C or 212F distilling off the solvent and theoretically leaving virtually no detectable levels in the oil if the proper techniques have been applied. However, microscopic portions of up to 25 parts per million (25 ppm) of hexane remain in the meal. Theoretically, hexane is represented by commercial vegetable oil companies to be completely removed in the recovery phase of the extraction cycle, but this cannot be guaranteed as manufacturing practices and quality control standards vary enormously from processor to processor.
In the mass market or conventional food industry the majority of vegetable oils sold as bottled product or as a food ingredient are solvent extracted oils. Mass market oils, however, are not labeled as solvent extracted. The predominant role of solvent extraction in commercial vegetable oils is largely economic. The greater efficiencies of solvent extraction is in maximizing yields and profits. It is why it has evolved into the most common form of oil removalit delivers the least expensive and lowest quality vegetable oils.
Stability (oxidive)
The relative resistance of a fat, oil, or food product to any undesirable type of breakdown or change in character is called stability. For fats and oils, stability may refer to resistance to oxidation, hydrolysis, rancidity, reversion and formation of off flavors.
Synergist (anti-oxidant)
A substance used in combination with another material which provides a greater specific effect than would be predicted by adding the sum of the effects obtainable from either material alone. Two antioxidants may be synergist (work in union chemically) when used in combination to retard oxidative stress or rancidity and product improved protection. Synergetic compounds act to create natural chemical reactions. Acidified clays contain synergist to bond certain types of impurities in the filter aid material, which allows a clear, clean oil to emerge from the bleaching/filtering operation.
Tempering/Conditioning (cooking)
This term means heating seed to uniform temperatures. The purpose of tempering is to remove any residual moisture in the seed so as to be able to obtain higher yields of oil. Most raw nuts, seeds, or bean stock are tempered or preheated using temperatures ranging from 49C or 120F, (as in safflower oil expelling) to 93C or 160F, (as in soy bean expelling).
Trans Fatty Acid
Trans fatty acids are synthetic saturated fats. They are generally man made, however can form naturally in cow's milk with up to 14% butter fat, but occur in vegetable fats only through hydrogenation. The hydrogen molecules attached at the center of the fatty acid carbon chain flips 180, which straightens the natural curve or kink in the typical cis-configured fat. When converted, the cis shape chemically alters to a trans configuration and hence is called a trans fat. Most margarine and vegetable shortening have been trans fat converted through full or partial hydrogenation process. Trans fats interfere with metabolic absorption efficiencies and tend to congregate at adipose tissue sites. They are difficult to excrete from the body and are a low quality energy source.
Trigliceride
A chemical unit composed of the reaction of one unit of glyceride with three units of fatty acids. All fats are made up of triglycerides. A typical fat or oil will be a physical mixture of many different types of triglycerides.
Unrefined Vegetable Oils
In the natural foods industry, the term unrefined vegetable oil is used for expeller pressed unrefined vegetable oils. It is assumed that calling an oil unrefined means that it is specifically not a crude oil. That is, it has not been integrated with some portion of solvent extracted oils. When labeled, unrefined oils should contain only 100% expeller pressed oil of the first pressing. Unrefined oils are processed using a higher standard of care. Tank and line flushing with inert gases, washing and purging of lines between different oils, and proper segregation of oils are all handling techniques used to insure healthier, better quality oils.
Unsaturated
Unsaturation is a term which describes the carbon makeup in the fatty acid portion of a fat or an oil. The term refers specifically to a shortage of hydrogen atoms in the carbon chain. The less hydrogen, the greater the degree of unsaturation and the number of reactive sites. Unsaturation in a fat or oil means easier formation of peroxides, easier development of rancidity, and greater tendency to polymerize (plasticize). Highly unsaturated fats are usually oils. Solid fats such as butter, tropical oils, coconut, or palm oil have higher saturation.
Virgin Olive Oil
The International Olive Oil Council (IOOC) has established trading standards which have been accepted by governments worldwide. The official nomenclature for olive oil designations are as follows:
Extra Virgin Maximum acidity not exceeding 1.0%
Fine Virgin Maximum acidity not exceeding 1.5%
Current Virgin or Virgin Maximum acidity not exceeding 3.0%
Pure A blend of fully refined olive oil (usually solvent extracted pumice oil with extra virgin or virgin olive oil). The virgin olive oil would be about 10-20% of the volume.
Lampante Means lamp oil and is an inedible industrial oil. It is usually oil recovered by solvents from the pumice and dregs of the oil extraction process.
Olive oil quality is a measurement of acidity. The higher the acidity the lower the quality. Peroxide values and free fatty acids vary with different types of olive oils. Olive oil varietals have wide flavor ranges, from very fruity and mild to very bitter, and they may still have low free fatty acid and peroxide values. The lower the values, the fresher the oil.
Olive oil typically is not sold directly after harvesting as it should be stored until the right maturation level is achieved. Olive oils are cured until sufficient flavor has been reached. There is no other commonly recognized commercial definition of virgin pertaining to other vegetable oils, and since the word has great significance and multiple permutations for olive oil, first pressing and virgin are not regarded as synonymous. Generally, there is only one pressing for vegetable oils, so first pressing is a meaningless term other than for olive oil. Second pressing usually involves the use of solvents for most other vegetable oils and therefore the term is misused when applied to oils other than olive.
The first olive oil pressing creates a mash or paste. The second pressing involves further hydraulic pressing and even solvent extraction to obtain the maximum release of oil from the olive oil cake. Because of these differences in extraction methods, claims of extra virgin, virgin, and pure should be clearly identified on the label to assure consumers that they are getting fair value. Frequently lower grade olive oil is blended with higher grade olive oil.
Winterization
Winterization is the processing of oils to remove waxes, styrenes and sterols. This is achieved by a chilling method using temperatures below 7.2C or 45F., with the addition of a filtering clay to remove phospholipid, stearin, waxes, esters and any solids or remnants in the oil. Winterized oils remove the chilled crystallized solids and result in an oil with a higher melting point. Winterized oils do not cloud in the refrigerator. Typically only fully refined oils are winterized. Unrefined oils can also be winterized on a selective basis. Winterization is an acceptable organic process when restricted to natural material such as diatomaceous earth.
Culinary Oil Extraction and Processing
Expeller processing of commercial nuts, beans, and seeds involves a number of sequential steps. Not all steps are necessary for all oils, but typically most oils labeled as refined are either fully refined (R.B.W.D.) or refined (R.B.D.). Alternate technologies for unrefined oils use only some of the steps noted below.
1. Cleaning, Hulling
A mechanical process where harvest trash, dust, dirt, and substandard seed is graded and only appropriate material isolated for processing. No heat or chemicals are used at this stage. However, during wet months, drying with propane fired machines may be used to bring high moisture levels in the unprocessed seed to within 7-11% of volume for proper storage and safety. This is necessary to keep seeds from decaying. No chemicals are applied here.
2. Flaking
This is used for materials which will be solvent extracted. Seed is desiccated and formed in a steam extruder ready for the solventizing tank. Heat friction and steam injection raises the temperature to 88C or 160F. in the formed cakes.
3. Cooking and Tempering
Tempering is used to bring moisture levels of seed to ranges permitting oil expelling. Cooking is used to bring seed micella cells up to the point where physical pressure will permit rupturing and release of oil content. Temperature ranges for both steps are 49 to 93C or 120 to 200F. depending on the seed type or bean stock being processed.
4. Pre-Press Expeller
This is an integrated machine which partially defats the meal prior to going to the solventizing plant for hexane removal of remnant fat. Pre-press expeller machines operates at high speeds and are intentionally not fully efficient because they rely on the secondary solvent process to remove the majority of the oil.
5. Full Press Expeller
This is the exclusive mechanical use of a screw or worm press which continuously processes the seed and removes the oil by simple friction and pressure. The temperature ranges of a full scale culinary oil expeller press is up to 60-71C or 140-160F. Temperatures will vary with seed types, seasons, and moisture content of the seed. Expellers can run with or without cookers/tempering bins, but yields are significantly lower without this added conditioning step.
6. Degumming/Super-Degumming
This process removes lecithin using water wash, citric acid or phosphoric acid, depending on the specifications of the operator (organic processing standards require water or citric acid only). Lecithin and water are centrifuged out leaving a cleaner more manageable oil. Some oils such as safflower do not need degumming as they are naturally gum free. However, soy and canola oils are not, and require degumming or super degumming prior to refining.
7. Alkali and Physical Refining
This refining process consists of alkali based agents used to process oils which are out of specification. High peroxide and free fatty acid values can be reduced using this process. The alkali is washed out along with reacted free fatty acids which have saponified (turned to soaps). The alkali is centrifuged out with no trace of alkali left in the oil. The alkali has become chemically bonded to the saponifiable acids as a captured free fatty acid. The capturing of free fatty acids and peroxides by the alkali base is the reason why the peroxides and free fatty acids drop after alkali refining.
Physical refining is the removal of free fatty acids and involves a modified form of steam deodorization. This method is largely employed in Europe as a solution to alkali refining. Vegetable oils are processed with longer duration and more efficient stripping of peroxides and free fatty acids in the steam tray column.
8. Bleaching and Filtering
The use of diatomaceous earth, acidified clay/non-acidified clays or adsorbents to remove colors and some odors from vegetable oils. Pigments are removed mechanically by using the clays. The filter aid or clay act as microscopic filters which remove the large color (chromaphore) molecule clusters and leave the long carbon chain fatty acids without pigments. Oils can be color modified from dark orange to a clear white. Temperatures for bleaching are typically 110C or 230F.
9. Deodorizing
Oil is pumped and deposited on rotating trays which is held in a vacuum column. Steam is injected which strips the remaining odors and flavors from the oil. The oil is then removed from the vacuum column. Temperatures range from 120-243C or 280-470F.).
10.Winterizing
For vegetable oils naturally high in waxes or stearins, further cloudiness is removed by chilling and filtering. Temperatures used are around 7.2C or 45F.
Contributed by Kathy Petal Pusher
http://thelibrary.luxurylane.com/reference/oils.htm
ever wanted to know about oil but were afraid to ask. :lol:
Cheers!
Signey
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All About Oils
From The Consumer's Guide to Using Oils for Flavor & Health
Vegetable oils are not all alike.
Some oils have more flavor. Some provide essential nutrients. Some hold up better to high heat or long storage. Some contain no pesticide residues.
Do you know which oil is which?
This document provides you quick, factual answers so that you can use each type of oil to its best advantage.
Proper packaging by the manufacturer and careful storage at home are both important to preserve nutrients and prevent rancidity in oils.
Heat, oxygen, and light are the most common damaging elements for vegetable oils. The more natural an oil, the more protection it needs. Oils properly sealed in glass containers, without oxygen trapped at the top (oxygen initiates deterioration), are quite stable until opened. Breaking the seal allows atmospheric oxygen to begin breaking down the oil. You can slow this process dramatically by refrigerating your oils once you've opened them.
Light can damage unrefined oils by reacting with chlorophyll and other bioactive components in the oil. Light-induced deterioration combined with oxidation can rapidly affect the status of vitamin E, carotene (vitamin A precursors), and other nutritive components of an oil. So, even if an attractive label tempts you to keep a bottle of oil on the counter, remember that it's best to keep the oil in the dark. Refined oils, however, are far less susceptible to light-induced damage.
Storage Guide
To safeguard the nutritive value and longevity of your oils, keep them in a cool 40F to 72F, dark cupboard until opening, and then store them in your refrigerator. Storage under these conditions provides a shelf life of 10-14 months for unrefined oils, and 14-20 months for refined oils. Freezing can extend an oil's shelf life. Again, refrigeration is not required but does improve shelf life.
Some Oils Are Environmentally Sound
Oils labeled "organic" are those pressed from seeds, nuts, or beans grown without the use of commercial pesticides, fungicides, fertilizer, or herbicides, and produced through cold-pressing or expeller-pressing processes. By consuming organic foods you minimize your intake of non-natural chemicals and help support the health of the environment.
Organic Guide
Any food that claims "organic" should bear a seal of certification from an independent third-party organization, such as the Organic Growers and Buyers Association. This seal assures quality, care, and commitment.
Some Oils Have Good Taste
The most flavorful oils are those left unrefined. Unrefined oils contain a number of biochemical compounds that provide flavor, scent, color, and nutrients. These compounds also reduce an oil's shelf-life stability. Unrefined oils are therefore the most flavorful, nutritious and the most sensitive to storage.
The refining process removes an oil's natural, bioactive compounds to achieve a uniform, neutral, stable product. Refined oils are therefore odorless and bland.
Why not always choose flavorful, unrefined oils? The answer depends on what you're cooking. Unrefined oils are more reactive to heat; in fact, they smoke and foam when used for frying or at temperatures above 375F. They also have a slightly higher moisture content, which makes them pop and fizz at medium to high temperatures. Refined oils, however, are stable at even high temperatures. The deep frying or other high-heat cooking, refined oils are the best choice.
Basic Facts on Fats and Oils
What Are Fats and Oils?
The word "fats" names a food group that includes what you probably think of as both fats and oils. Fats come from animal and plant Supplies and are usually solid at room temperature; oils are produced mainly from plants, and are liquid. The most common oils are extracted from seeds (safflower, sunflower, sesame, canola, flax), beans (peanuts, soy), grains (corn, wheat germ), fruits (avocado, olive), and nuts (almond, coconut, walnut, palm kernel).
Fats and oils are alike in that they're both made up of fatty acid molecules. You may already know the four basic types: saturated, monounsaturated, polyunsaturated, and superunsaturated. Because these fatty acids differ in their molecular structure, they differ in their behavior in your kitchen and in your body.
Saturated fatty acid molecules are shaped like a straight line, so they easily stack together into a compact mass. This dense form resist change, even when subjected to stresses such as air, heat, or light. For instance, a saturated fat is one that stays hard at room temperature and is slow to spoil (become rancid) butter and coconut oil are good examples.
Monounsaturated fatty acids have a single "kink" in their molecular strand. This kink makes them more fluid and more reactive than the unsaturated fats. Olive and canola oils are rich in monounsaturated fatty acids; you may have noticed that these oils get thick when you refrigerate them but they return to fluidity at room temperature.
Polyunsaturated fatty acids have two kinks, which makes them even more reactive molecules. Safflower and corn oils are well-known polyunsaturated oils. Both deserve careful handling to prevent rancidity.
The superunsaturated fatty acids are molecules with three kinks. These fats are rare and carry the most essential fatty acid nutrients. They are found mostly in fish tissue and in the seeds of the black currant, evening primrose, and flax plants. Superunsaturated oils are fluid at even very cold temperatures and react "firecracker" fast with oxygen. They must be carefully protected to preserve their nutritive qualities.
What Is a Cold-Pressed Oil?
Vegetable oils are generally produced through one of three processes: solvent extraction, mechanical (expeller) pressing, or cold pressing. Once produced, an oil can be left unrefined or can be put through a multi-step refining procedure.
Most mass market oils are obtained by solvent extraction, which involves the use of chemical solvents (some carcinogenic). They are also usually refined, a process during which temperatures can exceed 500F.
Mechanically (expeller) pressed oils are produced through a chemical-free, continuous mechanical process in which friction can generate temperatures of up to 185F. Refining removes a variety of naturally occurring materials to produce an oil that can withstand high heat without burning or releasing undesirable byproducts.
Cold-pressed oils are produced by a mechanical batchpressing process in which heat-producing friction is minimized so that temperatures remain below 120 F. The term cold-pressed, however, is frequently misapplied. True cold pressing involves the use of hydraulic presses or refrigerated in-line cooling devices on expeller presses.
What's the importance of heat in processing?
Heat is particularly influential in oil production because each 10 degree increase in temperature dramatically raises the rate at which the fatty acids react with oxygen, potentially destroying nutrients and promoting spoilage. Even after processing, heat is important because oils can be damaged if they are stored at warm/high temperatures.
Do Oils Go Rancid?
Oils spoil (become rancid) after prolonged contact with air (oxygen), light, and/or heat. You can identify a rancid unrefined oil by its unusually strong odor and sharp or bitter flavor. The off-odors are gases produced by the reactive fatty acid molecules; it's nature's way of letting you know the oil is past its prime.
Spoilage in refined oils is harder to detect because these oils have had their flavor and odor bodies removed. This makes refined oils far less susceptible to damage from light, heat, or oxygen exposure. Although their shelf-life is long (usually 24-30 months), deterioration can occur. Certainly, if you notice an unpleasant odor or flavor in refined oil, it's a sign of rancidity.
To protect your oils from spoilage, store them in a cool, dry place, out of harsh light. Alternatively, keep the oils you use daily in the refrigerator (note that to dissolve the solids in cold, unrefined oils you can just set the bottle in a bowl of warm tap water). Freezing is a good way to extend shelf life, especially with the super-reactive supplement oils (canola, flax, wheat germ) sold in plastic containers. Be careful, however, if you store glass bottles in the freezer, because the glass will become fragile.
It's also wise to purchase oils in small-sized bottles, because fresher oils are healthier oils.
OIL TERMINOLOGY IN THE NATURAL FOOD INDUSTRY
Listed below are some basic terms and definitions for natural oils and their processing.
Active Oxygen Method
Active oxygen method is an accelerated rancidity test in which the fat/lipids to be tested are held at a constant elevated temperature while air is bubbled upward through the hot fat/oil. Active oxygen stability (A.O.M.) is expressed as the number of hours of heating until a peroxide value (PV) of 100 milli-equivalent units has been reached. When reaching the level of PV=100, the oil has been determined to be fully rancid and not fit for human consumption.
Antioxidant
An antioxidant is any naturally occurring or manufactured material whose addition into a fat/lipid product provides increased oxidative stability. Antioxidants decrease oxidative stress by limiting chemical reactions and the uptake of single oxygen molecules from the atmosphere. Antioxidants interfere with the uptake of free oxygen from the atmosphere. Some oils already have high, naturally occurring antioxidants such as vitamin E, alpha, beta, gamma and delta tocopherols, sesamin, and sesamol. Natural oil soluble antioxidants, such as rosemary oil, vitamin E, (i.e., alpha-tocopherol) and other fat soluble compounds are occasionally added as antioxidant adjuncts to slow down the deterioration of vegetable oil and increase shelf life. All antioxidants must be US F.D.A. & US Department of Agriculture approved. Antioxidants which are synthetic are not regarded as natural adjuncts and therefore can not be included as ingredients of natural or organic oils.
Bleaching
Bleaching is the treatment of a fat or oil with activated carbon, diatomaceous earth, non-acidified and acidified clays, or any agent that removes color bodies and some odors from the fat or oil. Bleaching involves the mechanical straining of unrefined oils through plate and frame filters through a filter medium of bleaching clays and earth. The bleaching process uses paper or cloth filters which removes suspended compounds and delivers a more uniform lighter colored oil.
Canola Oil (Low Erucic Acid Rapeseed/LEAR) Canola oils pedigree originates from the brassica campestris family, or common mustard plant. It is a type of rapeseed originally bred in Canada, hence the name Canada oil or canola for short. It is high in monounsaturates, low in saturates and usually fully refined for use as a culinary oil. It has high levels of essential fatty acids (EFAs). It has 10% alpha-linolenic acid (Omega-3), which is a rare fatty acid in culinary oils. The erucic acid content in canola oil has been bred out. To be classed as a LEAR oil, the acid content of erucic has to be less than 2% of total fat. In most instances it is less than 1% in natural oil products and new breeding programs are lowering that value to less than 0.5% of total fat.
Cold Pressed/Processed Oil
For a number of years the term cold pressed has been erroneously used to describe oil removal using expeller pressed methods. The term has even been applied to refined oils (which expose oils to high temperatures from 243 to 470F during the refining process). Obviously this is a misnomer to the consumer who assumes cold pressing involves low temperature processing throughout. True cold pressing is legally defined in Europe as oil extraction at temperatures below 50C or 122F, and only to fully unrefined oils. True cold pressing occurs in:
1. The ancient method of stone grinding or milling, as in the crushing of olive oils
2. Bladder press extraction, which uses simple compression for fruit oils such as olive or avocado
3. Hydraulic presses, which uses simple compression
4. Low resistance expeller pressing, which controls screw worm, drive speeds and feed rates levels to temperatures which do not exceed 122F.
5. Modified Atmospheric Crushing (MAC) and Modified Atmospheric Packing (MAP), which employ enhanced cooling and refrigeration techniques using modified vegetable oil expeller presses that meet cold pressing temperature standards
MAC and MAP processing employs modified expeller presses. However, these presses are designed with in- line cooling devices to insure oils are kept below the temperatures called for in cold pressed oils. Proprietary engineering modifications make it possible to produce cold pressed oils using techniques that are more sophisticated, yet effective or even better than the older technology of simple mechanical cold pressing delivering superior nutritional oils.
Crude or Integrated Vegetable Oil
Typically solvent-extracted oil is blended with the first pressing of oil from a pre-pressed type expeller unit, which partially defats the meal. Pre-pressing leaves as much as half the oil in the seed. The rest is removed by solvents. The technique of blending pre-pressed expeller and solvent extracted oils is called integrated oil. The finished solvent/pre-pressed oils, when blended, are then sent off as crude oil for further refining. Basically, expeller pressing leaves about 5 to 13% of oil residual in the meal. Solvent processing leaves only 1 to 3% residual oil in the meal making it a more efficient processing method, yet a less healthy product. Solvents tend to concentrate in the meal. The meal is sold as animal feed. Excessive amounts of solvent in meal causes anemia in livestock. Hexane compounds are carcinogens according to the Environmental Protection Agency (E.P.A) and are classed as a hazardous substance. Hexane also poses a serious environmental threat as it is a hydrocarbon polluter and produces ozone and air pollution when it is vented into the atmosphere during the flash off cycle.
Crude is the term oil technicians use for either integrated unrefined vegetable oils or 100% solvent extracted oil before it moves on to be refined. Since it is at least a blend of expeller and solvent extracted oils, it is a misnomer to refer solely to expeller pressed unrefined oil as crude. Crude is a reference that only refers to large scale industrial extraction. It does not refer to unrefined oils that are processed at the cottage or intermediate industry level or for natural oils which employ greater standards of care and protection. Standard commercial extraction takes no additional precautions for sanitation, oxidation or high temperature protection. According to the USDA, crude oils are not considered fit for human consumption until they have been refined and impurities removed. The attitude in large scale refining operations is that the deterioration of the oil can be cleaned up through extensive refining.
Deoderizers
Deodorization of fats and oils removes reacted compounds which are decayed byproducts in the form of peroxidized fats. The process uses high vacuum, temperature, and live steam to remove strong flavors and odors from the fat or oil. Temperatures used in a deodorizing steam column are upwards to 200C or 450F. Lower temperatures (120C or 280F) are possible but longer exposure times are needed in the steam column to effectively remove impurities.
Essential Fatty Acids (EFAs)
Essential fatty acids (EFAs) are two fats that the human body cannot synthesize from other organic compounds or foods and are essential for life. They are Omega-6 (linoleic acid) and Omega-3 (alpha-linolenic acid). These acids are found abundantly in many vegetable oils. Both are classed as polyunsaturated fats. However, the alpha- linolenic acid (Omega-3 fraction) is also regarded as a super polyunsaturate. Proper handling and storage protection is needed as both fatty acids deteriorate rapidly in the presence of heat, light and oxygen.
Expeller Pressed
An expeller press is a screw type machine which presses oil through a caged barrel-like-cavity, using friction and continuous pressure from screw drives to move and compress the seed material. The oil spent (defatted) fiber is formed into a hardened cake which is released from the machine with the previously removed oil seeping through metal barrel slates that have small spacings to allow the oil to pass through without any seed fiber solids. Pressure involved in expeller pressing creates heat in the range of 60 - 99C or 140 - 210F).
Vegetable oils in the natural foods/health foods industry are almost all of the expeller pressed type. Expeller oil pressing is a mechanical rather than chemical extraction process. This method results in no solvents (such as hexane or other petroleum based distillents) residues left in the oil. It is the critical quality difference between refined oils often found in the natural foods marketplace as opposed to mass market or super market brands.
Fats and Oils
Fats and oils are called lipids which is their scientific name. Molecularly, they are long strings of carbon molecules which form triglycerides (or three fatty acid molecules tied to a glyceride molecule). Some have mono and diglyceride molecules which are one or two glyceride compounds. Fats and oils are a combination of one unit glyceride and three units fatty acids. Fat is normally semi-solid or solid at room temperature whereas an oil is normally liquid at room temperature. There are many types of fats and oils in nature. There are approximately 45 fatty acids fractions which make up fats.
Fatty Acid Profile
Fatty acids are formed through differing carbon chain lengths with either single, double, or triple bonds. Each oil has a different complex of fatty acids, which when broken down, identify its chemical signature. The four subgroups of fatty acids are the saturated, monounsaturated, polyunsaturated and super unsaturated fatty acids. Each group is characterized by increasing reactivity to heat, oxygen, and light energy. The longer the fatty acid chain the greater the instability and reactivity to oxygen, heat, and light energy. Saturated fat, with the shortest carbon chain length, is the most stable and least prone to oxidation. The super unsaturated oils are the longest chains of fats which have the least stability and shortest shelf life. On the other hand, the greater the reactivity to oxygen, heat, and light energy, the greater the use of the fatty acid as a nutritional supplement due to the hormone- like properties of these highly dense lipids.
Flavor
Flavors are indicative of an oil's value in its various commercial and food applications. Oils offer rich flavor bearing properties, provide texture, and enhance and compliment other flavors in foods. Describing oils by taste sensation involves highly subjective discriminations. Flavor variations may be described as bland, neutral, nutty, tallowy, fruity, or rancid. The properties associated with oils range from light to heavy, sweet to bitter, and fresh to rancid.
Free Fatty Acid (FFA)
Free fatty acid is the amount of fatty acid occurring naturally or produced as a byproduct in fat processing. Free fatty acids exist in an uncombined state as a definable chemical unit. This unit value is normally expressed as the breakdown of oleic acid. Free fatty acids are expressed as percent acidity calculated as oleic acid (a monounsaturated fat). The uncombined fatty acid comes from the breakdown of fat (as triglycerides) into a unit of fatty acid and glyceride.
First Pressing
Generally, there is only one pressing for vegetable oils, so first pressing is a meaningless term other than for olive oil. Second pressing usually involves the use of solvents for most other vegetable oils and therefore the term is misused when applied to oils other than olive.
High Oleic Oils
High oleic varieties are oil hybrids that have been genetically enhanced through selective plant breeding to produce high ratios of oleic acid (omega-9 fraction). The rise in oleic acid increases the oils stability and shelf life. High oleic oils have been bred to reduce polyunsaturated components and increase the monounsaturated content. High oleic oils should have at least 90% of the oleic content similar to olive oil. Olive oil is the benchmark for good culinary oleic based oils. This means that an oil should be at least 75% oleic by total fat content to be regarded as high oleic. High oleic oils perform well in medium to high heat cooking applications, such as deep frying or high heat sauteing.
Hydrogenated Fat and Oil
Hydrogenated fats are oils that have been processed through a chemical hardening method to achieve increased plasticity (stiffness) of the liquid oils at room temperature. Partial hydrogenation (brush hydrogenation) hardens oils but does not make them fully solid. Full hydrogenation requires complete conversion of a liquid oil into a solid fat at room temperature (72F). A fully hydrogenated oil has natural saturated fats left intact and all the remaining mono and polyunsaturated fatty acids become converted from their fluid cis-configuration to a full trans- fat rigid configuration. (See Trans Fatty Acids or Trans-Fats).
Hydrogenation Process
The hydrogenation process employs 1) high heat, 2) a metal catalyst such as nickel, zinc, copper, or other reactive metals, and 3) hydrogen gas. The metals are used to react with the hydrogen gas which is bubbled up through the mixture. The metals catalyze the hydrogen and carbon atoms and converts the cis-configured fatty acids by flipping one of the attached hydrogen molecules and rotating it half the diameter of the carbon chain. This effectively creates a new molecular shape resulting in a stiffer or more rigid material, hence the change from a liquid to a semi-solid or solid substance. This new shape stiffens with the hydrogenation process making the oil behave more like a saturated fat (such as coconut fat which is 92% saturation and solid at room temperature). Trans-fats are the result of this reaction. Partial hydrogenation or brush hydrogenation is a minimal conversion step which only offers a small degree of reaction by hydrogenation. Brush hydrogenation increases stability for volatile fatty acids like the Omega-3 (alpha-linolenic) and Omega-6 (linoleic) polyunsaturated oils. Most commercial salad dressing oils, such as soybean oil, have been brush hydrogenated. Hydrogenation raises the melting point of the fat and retards rancidity. But as recent health studies have found, other problems can ensue when consuming large amounts of trans fats from hydrogenated products.
Hydrolysis
A chemical reaction involving molecular breakdown by the reaction of an ester with water forming an acid and alcohol. It is a reaction between a fat or oil and water in the presence of various alkali agents, acids, metals lipase, or molds, which form new fatty acids and glyceride compounds. This reaction usually occurs under high temperatures and pressures. Hydrolysis also occurs when high degrees of moisture are naturally present in an oil. Over time, the vegetable oil will breakdown as a consequence of the hydrolytic action taking place between the fatty acids and the water content in the oil.
Iodine Value (IV)
Iodine values are used as signature markers for differing species or varieties of vegetable oils. Each oil has a specific iodine level and this ratio does not alter within the species. When oils are co-mingled with other species (i.e. canola and sesame oil) the iodine levels will be a value averaging between the normal iodine ranges typically found in each oil. This indicates that the oil is no longer a pure vegetable oil of one species, and some mixing has occurred to alter the iodine value. Iodine values are used to determine if tampering of oils has occurred.
Iodine value is an expression of the degree of unsaturation of a fat. It is measured by the amount of iodine which will react with a natural or processed fat under prescribed conditions. The iodine reacts with the chemically unsaturated hydrogen short group and is indicative of the degree of hydrogenation. When unsaturation is reduced, iodine values are lowered by hydrogenation. The iodine value is expressed as centigrams of iodine per gram of oil.
Isoelectric Dispersion Technology (IDT) (non-hydrogenated fats)
This is a licensed, patent-pending technology that converts a liquid fat into semi solid or solid fat at room temperature through a dispersion method which employs oil soluble thickening agents. The process breaks down fats to submolecular units with a very high degree of particulate dispersion. The IDT method avoids destructive use of high heat and caustic agents and provides a spreadable product without being hydrogenated. IDT methods are safer, healthier and gentler than traditional hydrogenation.
Modified Atmospheric Crushing and Modified Atmospheric Packing (MAC & MAP)
This is a class of processing which excludes light, heat, oxygen, and reactive metals in the presence of oils (used for nutritional supplements oils). Modified atmospheric packing (MAP) involves comprehensive refrigeration of oils during crushing, processing, settling, and filling of specifically designed bottles. This class of oil processing aims at employing as benign an extraction method as possible to keep nutrients and freshness intact. Temperatures do not exceed cold pressing ranges (less than 50C or 122F. The same care is employed in the bottle filling process which keeps the destructive influences of light, oxygen, heat, and reactive metals away from the oil. Encapsulated and bottled MAP products are stored and transported in inert, light proof materials, and kept refrigerated.
Oxidation
A chemical reaction involving the combination of single oxygen molecules randomly drawn from the atmosphere and combined with a reactive triglyceride molecule. Spoilage usually results from oxidative stress in foods. In oils, rancidity results in the formation of peroxides as a consequence of the free radical phenomena. Peroxidized levels past 100 megs/per kg. Are declared rancid by Department of Agriculture standards, and are a fraction of that level in supplement oils (usually not exceeding 5.0 PV in super unsaturated fatty acids). On the other hand, olive oil, which is deemed marketable at a starting PV of 20 experience high levels of peroxide formation and still can be considered safe and edible. Prior to being at a PV level of 20, the oil is considered immature and green. Peroxide values vary dramatically with different types of oil. The oil's intrinsic stability properties determine what the safety levels are. Sesame contains sesamin and sesamol, two very strong inhibitors which keep this oil naturally stable for very long periods of time. It is impossible to apply one standard for all oils as oils have very different properties, with different natural compounds that affect stability, taste and utility. Each oil has to be measured and tested on its own merits.
Peroxide Number (PV)
Peroxide value is a measure of the extent of oxidative absorption and entrainment of oxygen in a fat or oil. To properly interpret PV's, the age and handling history of the fat or oil must be known as peroxide values rise and fall on a bell curve with absorption and remission of oxidative levels in the oil, depending on the age of the oil. High peroxide usually indicates high degree of oxygen absorption. This value coupled with high free fatty acid (FFA) values indicates increased rancidity. If the value starts low, goes high and drops, and the second benchmark value continues to increase, the oil has become or is fully rancid and inedible. Peroxides can be lowered by reaction to bleaching, deodorization and alkali refining steps.
Photon Decay
Light is a form of energy and imparts chemical reactions in oils. Unrefined oils are more light sensitive as the chromaphores (color bodies) convert light/oxygen into free radicals through chlorophyll synthesis which is still active in the unrefined oil. This action continues to create lipase reactions and the ensuing breakdown product creates off flavors. Ketones, aldehydes and acetones are breakdown products producing off flavors in vegetable oils. The free radical process is most identified with light or photon decay and oxygen. Free radical formation is present throughout the process of decay and occurs as either alpha or beta types of oxidation. Alpha oxidation is oxygen drawn from the atmosphere, beta oxidation occurs from the entrained oxygen that is systematically present and produces reactions in the oil even while completely protected from outside influences such as heat, light and atmospheric oxygen. Long chained essential fatty acids are especially prone to light sensitivity and heat damage. Fully refined oils do not have the same potential because the trigger mechanisms of the chromaphores (color bodies) have been removed. Increasing free radical synthesis occurs with natural pigments in the oil. Refined oils have few or none and therefore have a much longer shelf life as compared to an unrefined pigment rich oil.
Rancidity
Rancidity is characterized by the development of off flavors, odors and colors. Rancidity in oils will usually result in a gag reflex if consumed by humans. Rancid oils have a bitter, high acrid after-taste which is easy to distinguish. Oxidative and hydrolytic stress also breakdown oils and speeds rancidity. Rancidity is measured as PV 100 meg/kg of sample tested.
Refining
Refining involves the removal of reacted compounds and decay compounds in the form of peroxidized fats and free fatty acids. Alkali refining employs a strong base, such as caustic soda, to consume the high acid content of reacted fats and bring the vegetable oil into American Oil Chemists Society standards (AOCS specification) and trading rules of the National Institute Of Oil Processors (NIOP). Most oils are sought to have peroxides brought back to a level of less than .05 megs/per kg. in a fully refined or purified vegetable oil. The follow-through steps of refining are:
1. Alkali refining, (to remove peroxides and impurities)
2. Centrifuging (to remove moisture and reacted fats, water washing)
3. A second centrifuging operation and finishing/polishing (in preparation for additional steps of deodorizing)
1. Bleaching (to remove color bodies)
2. Deodorizing (to remove odors and aromas)
3. Winterizing (to remove phospholipid, stearins, waxes and other compounds which crystallize in cold temperatures)
The description of full refining is R-B-D-W, which stands for the four steps of refining, bleaching, deodorizing, and winterizing. Not all refined oils are processed with all the steps. Organic refined oils use only natural agents such as citric acid and diatomaceous earth.
Reversion (flavor)
Reversion is a reversal of flavor properties where unfavorable off-flavors occur in an oil long after it has been refined. Off-flavors develop because polyunsaturated fats, particularly the Omega 3's, continue a rapid decline as they attract and absorb oxygen. Soybean and canola oil are subject to strong flavor reversion when improperly handled and under poor storage conditions. High storage temperatures, poor seals, or leaking bottles all invite quality deterioration.
Solvent Extraction
Solvent extraction is achieved through the desiccation or grinding of seed. The seed is then purged or washed with a petroleum distillate (such as hexane) to release the fat in the seed. The solvent is flashed off through heat in a sealed chamber. The oil/solvent blend is heated to 100C or 212F distilling off the solvent and theoretically leaving virtually no detectable levels in the oil if the proper techniques have been applied. However, microscopic portions of up to 25 parts per million (25 ppm) of hexane remain in the meal. Theoretically, hexane is represented by commercial vegetable oil companies to be completely removed in the recovery phase of the extraction cycle, but this cannot be guaranteed as manufacturing practices and quality control standards vary enormously from processor to processor.
In the mass market or conventional food industry the majority of vegetable oils sold as bottled product or as a food ingredient are solvent extracted oils. Mass market oils, however, are not labeled as solvent extracted. The predominant role of solvent extraction in commercial vegetable oils is largely economic. The greater efficiencies of solvent extraction is in maximizing yields and profits. It is why it has evolved into the most common form of oil removalit delivers the least expensive and lowest quality vegetable oils.
Stability (oxidive)
The relative resistance of a fat, oil, or food product to any undesirable type of breakdown or change in character is called stability. For fats and oils, stability may refer to resistance to oxidation, hydrolysis, rancidity, reversion and formation of off flavors.
Synergist (anti-oxidant)
A substance used in combination with another material which provides a greater specific effect than would be predicted by adding the sum of the effects obtainable from either material alone. Two antioxidants may be synergist (work in union chemically) when used in combination to retard oxidative stress or rancidity and product improved protection. Synergetic compounds act to create natural chemical reactions. Acidified clays contain synergist to bond certain types of impurities in the filter aid material, which allows a clear, clean oil to emerge from the bleaching/filtering operation.
Tempering/Conditioning (cooking)
This term means heating seed to uniform temperatures. The purpose of tempering is to remove any residual moisture in the seed so as to be able to obtain higher yields of oil. Most raw nuts, seeds, or bean stock are tempered or preheated using temperatures ranging from 49C or 120F, (as in safflower oil expelling) to 93C or 160F, (as in soy bean expelling).
Trans Fatty Acid
Trans fatty acids are synthetic saturated fats. They are generally man made, however can form naturally in cow's milk with up to 14% butter fat, but occur in vegetable fats only through hydrogenation. The hydrogen molecules attached at the center of the fatty acid carbon chain flips 180, which straightens the natural curve or kink in the typical cis-configured fat. When converted, the cis shape chemically alters to a trans configuration and hence is called a trans fat. Most margarine and vegetable shortening have been trans fat converted through full or partial hydrogenation process. Trans fats interfere with metabolic absorption efficiencies and tend to congregate at adipose tissue sites. They are difficult to excrete from the body and are a low quality energy source.
Trigliceride
A chemical unit composed of the reaction of one unit of glyceride with three units of fatty acids. All fats are made up of triglycerides. A typical fat or oil will be a physical mixture of many different types of triglycerides.
Unrefined Vegetable Oils
In the natural foods industry, the term unrefined vegetable oil is used for expeller pressed unrefined vegetable oils. It is assumed that calling an oil unrefined means that it is specifically not a crude oil. That is, it has not been integrated with some portion of solvent extracted oils. When labeled, unrefined oils should contain only 100% expeller pressed oil of the first pressing. Unrefined oils are processed using a higher standard of care. Tank and line flushing with inert gases, washing and purging of lines between different oils, and proper segregation of oils are all handling techniques used to insure healthier, better quality oils.
Unsaturated
Unsaturation is a term which describes the carbon makeup in the fatty acid portion of a fat or an oil. The term refers specifically to a shortage of hydrogen atoms in the carbon chain. The less hydrogen, the greater the degree of unsaturation and the number of reactive sites. Unsaturation in a fat or oil means easier formation of peroxides, easier development of rancidity, and greater tendency to polymerize (plasticize). Highly unsaturated fats are usually oils. Solid fats such as butter, tropical oils, coconut, or palm oil have higher saturation.
Virgin Olive Oil
The International Olive Oil Council (IOOC) has established trading standards which have been accepted by governments worldwide. The official nomenclature for olive oil designations are as follows:
Extra Virgin Maximum acidity not exceeding 1.0%
Fine Virgin Maximum acidity not exceeding 1.5%
Current Virgin or Virgin Maximum acidity not exceeding 3.0%
Pure A blend of fully refined olive oil (usually solvent extracted pumice oil with extra virgin or virgin olive oil). The virgin olive oil would be about 10-20% of the volume.
Lampante Means lamp oil and is an inedible industrial oil. It is usually oil recovered by solvents from the pumice and dregs of the oil extraction process.
Olive oil quality is a measurement of acidity. The higher the acidity the lower the quality. Peroxide values and free fatty acids vary with different types of olive oils. Olive oil varietals have wide flavor ranges, from very fruity and mild to very bitter, and they may still have low free fatty acid and peroxide values. The lower the values, the fresher the oil.
Olive oil typically is not sold directly after harvesting as it should be stored until the right maturation level is achieved. Olive oils are cured until sufficient flavor has been reached. There is no other commonly recognized commercial definition of virgin pertaining to other vegetable oils, and since the word has great significance and multiple permutations for olive oil, first pressing and virgin are not regarded as synonymous. Generally, there is only one pressing for vegetable oils, so first pressing is a meaningless term other than for olive oil. Second pressing usually involves the use of solvents for most other vegetable oils and therefore the term is misused when applied to oils other than olive.
The first olive oil pressing creates a mash or paste. The second pressing involves further hydraulic pressing and even solvent extraction to obtain the maximum release of oil from the olive oil cake. Because of these differences in extraction methods, claims of extra virgin, virgin, and pure should be clearly identified on the label to assure consumers that they are getting fair value. Frequently lower grade olive oil is blended with higher grade olive oil.
Winterization
Winterization is the processing of oils to remove waxes, styrenes and sterols. This is achieved by a chilling method using temperatures below 7.2C or 45F., with the addition of a filtering clay to remove phospholipid, stearin, waxes, esters and any solids or remnants in the oil. Winterized oils remove the chilled crystallized solids and result in an oil with a higher melting point. Winterized oils do not cloud in the refrigerator. Typically only fully refined oils are winterized. Unrefined oils can also be winterized on a selective basis. Winterization is an acceptable organic process when restricted to natural material such as diatomaceous earth.
Culinary Oil Extraction and Processing
Expeller processing of commercial nuts, beans, and seeds involves a number of sequential steps. Not all steps are necessary for all oils, but typically most oils labeled as refined are either fully refined (R.B.W.D.) or refined (R.B.D.). Alternate technologies for unrefined oils use only some of the steps noted below.
1. Cleaning, Hulling
A mechanical process where harvest trash, dust, dirt, and substandard seed is graded and only appropriate material isolated for processing. No heat or chemicals are used at this stage. However, during wet months, drying with propane fired machines may be used to bring high moisture levels in the unprocessed seed to within 7-11% of volume for proper storage and safety. This is necessary to keep seeds from decaying. No chemicals are applied here.
2. Flaking
This is used for materials which will be solvent extracted. Seed is desiccated and formed in a steam extruder ready for the solventizing tank. Heat friction and steam injection raises the temperature to 88C or 160F. in the formed cakes.
3. Cooking and Tempering
Tempering is used to bring moisture levels of seed to ranges permitting oil expelling. Cooking is used to bring seed micella cells up to the point where physical pressure will permit rupturing and release of oil content. Temperature ranges for both steps are 49 to 93C or 120 to 200F. depending on the seed type or bean stock being processed.
4. Pre-Press Expeller
This is an integrated machine which partially defats the meal prior to going to the solventizing plant for hexane removal of remnant fat. Pre-press expeller machines operates at high speeds and are intentionally not fully efficient because they rely on the secondary solvent process to remove the majority of the oil.
5. Full Press Expeller
This is the exclusive mechanical use of a screw or worm press which continuously processes the seed and removes the oil by simple friction and pressure. The temperature ranges of a full scale culinary oil expeller press is up to 60-71C or 140-160F. Temperatures will vary with seed types, seasons, and moisture content of the seed. Expellers can run with or without cookers/tempering bins, but yields are significantly lower without this added conditioning step.
6. Degumming/Super-Degumming
This process removes lecithin using water wash, citric acid or phosphoric acid, depending on the specifications of the operator (organic processing standards require water or citric acid only). Lecithin and water are centrifuged out leaving a cleaner more manageable oil. Some oils such as safflower do not need degumming as they are naturally gum free. However, soy and canola oils are not, and require degumming or super degumming prior to refining.
7. Alkali and Physical Refining
This refining process consists of alkali based agents used to process oils which are out of specification. High peroxide and free fatty acid values can be reduced using this process. The alkali is washed out along with reacted free fatty acids which have saponified (turned to soaps). The alkali is centrifuged out with no trace of alkali left in the oil. The alkali has become chemically bonded to the saponifiable acids as a captured free fatty acid. The capturing of free fatty acids and peroxides by the alkali base is the reason why the peroxides and free fatty acids drop after alkali refining.
Physical refining is the removal of free fatty acids and involves a modified form of steam deodorization. This method is largely employed in Europe as a solution to alkali refining. Vegetable oils are processed with longer duration and more efficient stripping of peroxides and free fatty acids in the steam tray column.
8. Bleaching and Filtering
The use of diatomaceous earth, acidified clay/non-acidified clays or adsorbents to remove colors and some odors from vegetable oils. Pigments are removed mechanically by using the clays. The filter aid or clay act as microscopic filters which remove the large color (chromaphore) molecule clusters and leave the long carbon chain fatty acids without pigments. Oils can be color modified from dark orange to a clear white. Temperatures for bleaching are typically 110C or 230F.
9. Deodorizing
Oil is pumped and deposited on rotating trays which is held in a vacuum column. Steam is injected which strips the remaining odors and flavors from the oil. The oil is then removed from the vacuum column. Temperatures range from 120-243C or 280-470F.).
10.Winterizing
For vegetable oils naturally high in waxes or stearins, further cloudiness is removed by chilling and filtering. Temperatures used are around 7.2C or 45F.
Contributed by Kathy Petal Pusher
http://thelibrary.luxurylane.com/reference/oils.htm