Proteins are organic molecules that are essential to life. In the cells of organisms, they perform several roles. Importantly, they function as structural components of cells, and when water soluble, they function as enzymes that catalyze reactions. Organic catalysts initiate chemical reactions without being part of them. Chemically, proteins are composed of linear polymers of 20 different amino acids. These amino acids, in turn, are arranged in various sequences called “primary structures,” which determine the way amino acid chains are folded—three-dimensionally—to produce proteins with specific functions. Polypeptides are small proteins of fewer than 100 amino acids; highly complex, large-molecular proteins may have many thousands of polypeptides. Based on these structural distinctions, some proteins—such as collagen—form the fiber of animal tissues, whereas other proteins—those with very complex shapes—may become enzymes.

The brewer has a complex relationship with proteins, which are looked upon as both a curse and a blessing. The nitrogenous compounds that concern the brewer start with nitrogen uptake from soil in the grain fields and then follow through the entire brewing process into the beer drinker’s glass. Protein management throughout the malting and brewing process, therefore, is an essential part of making good beer, or, in fact, any beer at all.

Proteins, in the form of enzymes, are the key organic catalysts that break down components in raw barley and make them process compliant for such operations as lautering and filtration and finally suitable for yeast to metabolize during fermentation. Without enzymes doing their catalytic work, we could not break down grain starches into sugars and yeast would, quite literally, have nothing to ferment. Enzymes convert large-molecular starches into yeast-fermentable sugars; they reduce large-molecular proteins into smaller ones, including amino acids, which are essential for healthy yeast growth and development. See alpha amylase, free amino nitrogen (fan), modification, proteolysis, and yeast nutrients. Enzymes perform these functions at various stages in the malting plant and in the mashing vessel. The brewer will use the mashing profile to break down certain proteins and leave others intact. The breakup of large-molecular proteins reduces mash viscosity and thus enhances the ability of the brewer to extract sugars through the grain bed during lautering. See fermentation, lautering, malt, mashing, and protein rest.

As malt and other grains become wort, proteins take on other roles, and the brewer begins to attempt to manipulate the protein profile of both the wort and the finished beer. The boiling of the wort coagulates and precipitates proteins that, left intact, would make the resulting beer opaque, viscous, and unstable. In the kettle and whirlpool, proteins leave the wort as a granular sediment called trub. Kettle finings, such as carageenan derivatives, may be added to assist the coagulation and help settle out the trub. Later, after the wort is cooled, more protein will sediment out during the “cold break.” The brewer may hope to avoid protein-derived hazes and sediments in beer that is destined to be filtered bright, but he must not go too far. Beer without proteins would have little body or mouthfeel; it would taste thin and empty. The sturdy crown of foam that is prized on most types of beer is largely created by proteins; remove these “foam-positive” proteins, and the beer may end up without proper tactile and visual texture—foamless, wan, and unattractive. Brewing may seem, at its core, to be a simple art, but a look at the conflicting roles of proteins is a window into the true complexity of modern brewing.

See also chill haze, cold break, foam, and kettle finings.