is a general biochemical term covering the breakdown of proteins into peptides and eventually amino acids. In relation to brewing the term refers to one or more steps in step infusion or decoction mashing processes. These steps are in the temperature range between 113oF (45oC) and 131oF (55oC) where the malt’s naturally occurring proteolytic enzymes are active. The practical effects of this proteolytic rest are highly questionable, as the theory behind these, as many other older, traditional mashing dogma, stems from a time when the quality of malts was far inferior to those of today. Furthermore, some have suggested that proteolysis does not occur in mashes, even at low temperatures, because of the inhibition of the necessary enzymes.

The older brewing literature and the legends within certain schools of thought in brewing theory say that proteolysis produces more free amino acids needed as nutrients by the yeast, that it helps to form more amylolytic enzymes, thus aiding starch conversion, and that by removing part of the soluble protein improves the chemical stability of the beer. Newer literature and more modern schools of thought claim that the positive effects of proteolysis are negligible, and that the only significant effect is negative as the content of foam active proteins in the finished beer is reduced. As the temperature range for proteolysis coincides very closely with the optimum range for the natural malt beta- glucanases, it is likely that some of the positive effects, previously assigned to proteolysis, were in fact a result of beta-glucan breakdown.

See also mashing, protein rest.