Full text loading...
Chapter 40 : Beer
This chapter provides a overview of the scientific principles of the brewing industry. Conversion of starch into simple sugars happens during mashing, and the changes during malting are limited to the breakdown of cell walls and the protein matrix in which the starch granules are embedded, but such modification of the grain is necessary for hydrolysis of the starch during mashing. It is now recognized that hops have an important antimicrobial, particularly antibacterial, effect, and it is presumed that the medieval brewers realized that hopped beers maintained their quality for longer periods of time than did beers with other flavorings. Formerly, the actively fermenting yeasts of the fermentation industries, both culture yeasts and common contaminant “wild yeasts,” were classified as different species of Saccharomyces. Most of these species are now classified officially by yeast taxonomists as a single species, S. cerevisiae, but still it is convenient in the brewing industry to distinguish the different types by their former specific names.Enterobacteria (including Obesumbacterium, the most important of that group in the brewery environment) cause turbidity and off-flavor and often produce indole, phenols, diacetyl, hydrogen sulfide, and dimethyl sulfide, but grow well in the early stages of fermentation until inhibited by the falling pH and increasing ethanol content. Megasphaera (cocci) and Pectinatus (rods) species are recently discovered strictly anaerobic gram-negative bacteria which form acetic, butyric, and propionic acids, hydrogen sulfide, dimethyl sulfide, and turbidity and have become troublesome only because of modern advances in maintaining very low dissolved oxygen levels in beer.