Beer Yeast

Yeast is a single celled microorganism that is used in fermentation of liquids and breads. Beer yeast, can be classified into two different strains.  These strains are called ale yeast (top fermenting yeast, or Saccharomyces cerevisiae) and lager yeast (bottom fermenting yeast, or Saccharomyces uvarum). Due to reclassification of yeast strains, both are considered members of S cerevisiae family. Top fermenting strains are best used in certain temperature. They receive their name because much of the fermentation action occurs at the top of a fermenter. This creates thick, rich yeast head. Ale yeasts like warmer temperatures where fermentation can occur between 50°F -68°F. Fermentation of these yeasts can produce beers in high esters. Esters are chemical compounds that produce a variety of fruity flavors in beer. Top fermenting yeasts are mostly used to create wheat beers, brewing ales, porters, and stouts. Bottom fermenting yeast receives its name from fermentation of yeast. The settles out at the bottom of a fermenter. They grow less rapidly than top fermenting yeast which produces less surface foam. The flavor of beer depends on the strain of the lager yeast and which temperature it is fermented at. Their fermentation temperatures can range from 44°F – 59°F. Common styles are Pilsners, Dortmunders, Bocks and American malt liquors.  Interestingly, using lager yeasts at higher temperatures produces a style of beer called California Common Beer. This style of beer requires larger yeast to be used at 60°F -70 °F. Beer yeasts can vary in production temperatures, place of fermentation, and flavor.