What is the purpose of nutritional yeast?

Question

I have several recipes for seitan which call for nutritional yeast. I've never used it before and am curious about its purpose.

Is it for flavor, texture, nutritional value?

Answer

This product is new to me, but it looks interesting.

The flavour of nutritional yeast is described in Wikipedia:

Nutritional yeast has a strong flavor that is described as nutty, cheesy, or creamy, which makes it popular as an ingredient in cheese substitutes. It is often used by vegans in place of parmesan cheese.

Nutritional yeast is a so called complete protein.

A complete protein (or whole protein) is a source of protein that contains an adequate proportion of all nine of the essential amino acids necessary for the dietary needs of humans or other animals.

This also explains why it is popular among vegans, that needs to replace the amino acids in meat with alternative food sources.

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