Amino Acids. Proteins, especially enzymes, occupy a unique and important position in cell metabolism, and their biosynthesis from amino acids is one of the less secretive aspects of biology. Proteins are mostly constructed of linear, covalently bonded chains of amino acids.

From a brewing point of view, free amino acids are of most significance during fermentation, where they are the most readily available nitrogen source for yeast. See free amino nitrogen (fan). They are derived from malt and wort, and are critical to fermentation performance and beer quality. The uptake of wort amino acids involves a number of permeases: a broad-spectrum general amino acid permease (GAP) and several specific for an individual acid. Sixteen different amino acid transport systems have been identified in yeast (12 being constitutive and 4 (including the high-affinity GAP) being regulated by nitrogen sources already present in wort—called nitrogen catabolite repression).

A typical all-malt wort contains some 19 amino acids and these are taken up by yeast at differing rates. In order to achieve a good, rapid, fermentation the α-amino acid content of wort should be not less than 100 mg l^–1, preferably in the region of 150–200 mg l^–1. There should also be a balance of amino acids for the yeast to utilize. Commercial yeast nutrients often provide trace zinc and a range of amino acids.