While baking, salt and live yeast are usually never mixed together, since salt reacts with live yeast and instantly and irrevocably kills the yeast, due to which it becomes absolutely useless for gas generation. Hence, bakers always maintain one layer between the live activated yeast and added salt. However, salt is sometimes deliberately added to live yeast to get an entirely new food ingredient called autolyzed yeast extract, after undergoing certain processes. It is a substantial source of MSG (monosodium glutamate) and is widely used as a flavor enhancer in a number of food products we consume.
When salt and live activated yeast come into contact with one another, a chemical process called autolysis takes place―the self-destruction or self-digestion of an organism by its own enzymes. Salt does not kill the yeast as commonly said, but causes the live yeast's digestive enzymes to eat itself. This creates inactive yeast, which has a different concentration of proteins. The product then undergoes a secondary process to get another byproduct, called autolyzed yeast extract.
People who are intolerant towards gluten, often ask if whether autolyzed yeast extract is gluten-free, where the answer to this question is, yes. However, it is important to know that it does contain MSG. If a person is sensitive or allergic in any way to MSG, he should avoid foods that contain traces of this. It doesn't contain soy, too.
It is often used as a less expensive substitute for MSG, but many health advocates have voiced a negative opinion vociferously against this practice. The proponents on the other hand, claim that there are no harmful effects of this product. Hence, as far as the health benefits are concerned, it is very difficult to state whether it is okay for consumption, or not. It is popularly used in Asian cuisines, like Chinese. Because it is high in protein, it is used to give a hearty flavor that is similar to beef, and is used in processed foods to lend it a meaty or savory undertone.
It is used primarily as a flavor enhancer in a lot of processed foods such as soups, processed meats, as well as a number of vegetarian food products. If you want to check if a certain product does contain autolyzed yeast extract, you'll have to check the packaging's ingredient list. It is often mentioned simply as 'yeast extract'. Other names that this kind of yeast is called are, 'corn gluten yeast extract', 'yeast hydrolysate' and 'dried yeast hydrolysate'. At the same time, there are certain manufacturers who don't like to mention it as an ingredient; to be more precise, they are reluctant about mentioning this on food packaging. A number of broths and sauces do contain it, which means you will have to spend more time at the supermarket inspecting food products.