That's true Mike, if the store bought Kefir were real it would explode. There is a sauerkraut that I buy from time to time called Bubbies, HEB and Sprouts sells it. It is supposed to be real fermented kraut but after reading their web-site they admit that they had to begin using heat when canning them in the jars because they were oozing out in the stores.
When you make Kefir the gas has to escape.