E621 first referred to monosodium glutamate, or MSG, years before it meant related to furries. MSG is a flavor enhancer found in many foods. E621 is what’s known as the E number (a standardized code for substances in Europe) for MSG.

Artificial flavour enhancers are usually the additive E621. It is chemically identical to the body's own glutamate. E621, often also known as monosodium glutamate (MSG), is one of the best-known flavour enhancers and is widely used both in industry and in private households.

Additive : E621 - Monosodium glutamate Functions: Flavour enhancer Monosodium glutamate -MSG, also known as sodium glutamate- is the sodium salt of glutamic acid, one of the most abundant naturally occurring non-essential amino acids.

MSG is a white, odorless, crystalline powder commonly used as a food additive. In the food industry, it’s known as E621. It dissolves easily in water, separating into sodium and free glutamate (2). It’s made by fermenting carb sources like sugar beet, sugar cane, and molasses (3).