In general baking terms, salt and live yeast should never meet directly because only bad things can happen. The salt will instantly and irrevocably kill the yeast, rendering it completely useless for gas generation. This is why bakers will keep at least one layer of ingredients between the live activate yeast and any added salt. When salt is deliberately added to live yeast, however, it becomes an entirely new food ingredient known as autolyzed yeast.

The interaction between salt and live yeast creates a chemical process called autolysis. Autolysis is essentially the self-destruction or self-digestion of an organism by its own enzymes. Salt does not "kill" yeast as much as it causes the live yeast's digestive enzymes to eat themselves. The result is an inactive yeast with a different concentration of proteins. This new food product can be further processed to create autolyzed yeast extract.

Many people may not recognize autolyzed yeast as an ingredient in many of their favorite processed foods, but they might recognize an ingredient derived from it: MSG, or monosodium glutamate. Both autolyzed yeast and MSG are used as flavor enhancers in processed foods or Asian foods prepared in restaurants. Autolyzed yeast extract is also used by itself in processed food spreads such as Vegemite. Because of its high protein content, autolyzed yeast generally has a hearty flavor similar to beef, which is why it is often used to give processed foods a meaty or savory undertone.

Both MSG and autolyzed yeast enhance the flavor of food by chemically altering the consumer's taste buds. Both contain a substantial amount of free glutamic acid, an enzyme which makes it easier for the taste buds to detect savory or meaty flavors. Other spices and flavorings can be added to autolyzed yeast and applied to snack foods such as crackers, corn chips or potato chips. The free glutamic acid enhances the flavor of the other seasonings.

There is some controversy over the use of autolyzed yeast and other flavor enhancers, however. A number of people are extremely sensitive to MSG, which can trigger a condition known as a "Chinese restaurant headache." Specifically, the sodium and the glutamates found in both autolyzed yeast and MSG can trigger an allergic reaction in certain people.

While certain food manufacturers may not want to list MSG as an ingredient in processed foods, the same reluctance does not always extend to autolyzed yeast. Many consumers may not be aware of the direct connection between autolyzed yeast and its derivative known as monosodium glutamate. Any food additive containing significant levels of free glutamic acid can trigger the same general allergic reaction as MSG, but those ingredients are not as well-publicized as monosodium glutamate.