What acid is in mutton and beef?

Mutton and beef don't contain any specific "acid" in the way that you might find in a lemon or vinegar.

However, they do contain lactic acid, which is produced by the breakdown of glycogen in muscle tissue after an animal dies. This process contributes to the sour taste and tenderization of meat.

Additionally, during digestion, our stomach produces hydrochloric acid which is essential for breaking down proteins in meat.

So while there isn't a single "acid" that defines mutton and beef, lactic acid plays a key role in their flavor and texture, and hydrochloric acid helps us digest them.