I have another question about deep fry fat.

I've noticed that when I pour my deep fry fat back in the jars, it's often more runny than beforehand. In particular, it tends to separate into solid and liquid parts, with the liquid darker in color and floating on the top.

I always thought that heat causes fat to polymerize or become more saturated, and I expected that would make it more solid. Why does it end up more liquid?

The second part of the question is this: Is the liquid fat more burned than the solid? Should I pour it off and just use the solid part?

Ok, at your request looking in my H. McGee book. It talks about smoke point and says:

"Most fats do nothave sharply defined melting points. Instead, they soften gradually over a braod temperature range. As the temperature rises, the different kinds of fat molecules melt at different points and slowly weaken the whole structure..." Ok, that's probably much lower temperature

"The characteristic temperature at which a fat breaks down into visible gaseous products is called the smoke point. Not only are the smoky fumes obnoxious, but the other materials that remain in the liquid, including chemically active free fatty acids, tend to ruin the flavor of the food being cooked.

... animal fats around 375. (smoke point)

Fats that ocntain other substances (butter, proteins or carbs) will smoke at lower temperatures.

Fat breakdown during deep frying can be slowed by using a tall, narrow pan and so reducing the area of contact between fat and atmosphere.

The smoke point of a deep-frying fat is lowered every time it's used, since some breakdown is inevitable even at moderate temperatures, and trouble-making particles of food are always left-behind.

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Saturation would do the exact opposite of what you are describing, it'd make your fat thicker, like coconut oil, right?

Hydrogenation requires you to add nickel to the oil as a catalyst then expose it to hydrogen gas at high temperature and pressure, then filter out the nickel. You're probably not doing that! Besides, it'd turn your oil into a solid fat.

Thanks!

Now, if only someone can explain why it becomes more liquid...

Do you mean you're using a saturated fat and it isn't becoming a solid after you deep fry with it?

It sounds like heating causes the structure to break down some, more free fatty acids. Maybe that is why? Saturated fats are straight compared to unsaturated ones, and tend to lock together like a zipper.

That's right. About half of it is solid and light colored and sits at the bottom of the jar. On top of that floats a golden-brown liquid. So maybe pouring off the liquid would improve the quality of the fat.

Maybe you should pour off the liquid part and reuse the solid part. Oh you said that!

Sorry, I'm editing while you're posting, so this conversation is getting all out of order!

What is the source of the fat you're using? Maybe it has some proteins in it?

It's mostly lard that I rendered myself, so no doubt there are some proteins.

I wonder if filtering it through a coffee filter after rendering might get rid of those proteins?

Maybe I should get a coffee filter. I've used cheesecloth occasionally, but when the fat is hot enough to flow through the cheesecloth, it's also hot enough to shatter some of my jars. I think what I really need is a collection of metal lard cans.

Or metal coffee cans. They're perfect.

Oh yeah! I just saved one a couple weeks ago, thinking it might prove useful. I didn't think about how, though!

I gave the liquid fat a last hurrah tonight. My 4-year old asked if she could eat a potato that my mother-in-law had bought. So I made french fries.

Well, it seemed like a good idea, but the fat solidified before it all dripped through the filter...!