Beer: An Ancient Yet Modern Biotechnology

The brewing of beer is a complex process that draws on a diversity of sciences and technology, of which chemistry is but one. This paper focuses on the chemistry of the brewing process and of the finished product. It examines each of the main classes of molecule found in beer, considers their contribution to quality and their origins in the brewing process. The study of beer and its production provides an excellent illustrative example for teaching how raw materials and the manner by which they are processed determine the acceptability of a product. Beer, whilst 90%+ water, contains a wide range of chemical species which establish its properties. Apart from ethanol (the common denominator amongst all alcoholic beverages), beer contains substances that determine its flavor, foam, and color. The flavorsome components of beer include the bitter iso-a-acids and aromatic essential oils from hops, along with esters, acids, sulfur-containing compounds and vicinal diketones from yeast. The foaminess of beer depends on the presence of carbon dioxide but also of surface-active materials like amphipathic polypeptides from malt and the bitter substances from hops. The color is due to Maillard reaction products generated largely during the kilning of malt. The malting and brewing processes (which are briefly described) are designed to maximize the extraction and digestion of barley starch and protein, yielding highly fermentable wort. The processes are also designed to eliminate materials that can have an adverse effect on beer quality, such as the haze-forming polyphenol from barley and hops and the lipids and oxygen that, together, can cause beer to stale.