Chapter 4


(book excerpts)

Yeast is one of the most important ingredients in brewing beer responsible for metabolic processes that produce ethanol, carbon dioxide, and a whole range of other metabolic byproducts that contribute to the flavor and finish of beer. There are literally hundreds of varieties and strains of yeast. In the past, there were two types of beer yeast: ale yeast (the “top-fermenting” type, Saccharomyces cerevisiae) and lager yeast (the “bottom-fermenting” type, Saccharomyces pastorianus, formerly referred to as Saccharomyces carlsbergensis or Saccharomyces uvarum). Functionally these yeasts differ in their optimum fermentation temperatures, ability to ferment different sugars, environmental conditions, and ability to settle out upon completion of fermentation, and production and/or metabolism of fermentation by-products. Top fermenting yeasts produce beers that are more estery, fruity, and sometimes malty, whereas bottom-fermenting yeasts give beers a characteristic sulfurous aroma. Some other notable differences also include fermentation temperatures and flocculation characteristics. Top-fermenting yeasts are used for brewing ales, porters, stouts, Altbier, Kölsch while bottom-fermenting yeasts are used for brewing lagers such as Pilsners, Dortmunders, Märzen, and Bocks. Nowadays, the differentiation in ale and lager yeasts is not as distinct given the fact that beers are widely fermented in similar vessels (cylindroconical tanks) and because of other advances in brewing science.

Click on the following topics for more information on yeast.

Topics Within This Chapter:

  • Brewer’s Yeast
  • Ale Yeast
  • Lager Yeast
  • Brettanomyces Yeast
  • Yeast Life Cycle
  • The Lag Phase
  • The Growth Phase
  • The Fermentation Phases
  • The Sedimentation Phase
  • Yeast Nutritional Requirements
  • Carbohydrates
  • Nitrogen
  • Vitamins
  • Molson Coors Brewing Company
  • Minerals
  • Yeast Viability and Vitality
  • Cell Viability
  • Cell Vitality
  • Factors Influencing Viability and Vitality
  • Large Brewers
  • Factors Affecting Beer Sales
  • Yeast Strain Selection
  • Attenuation
  • Beer Flavor
  • Degeneration of Yeast
  • Flocculation
  • Mutation of Yeast
  • Yeast Byproducts
  • Acetaldehydes
  • Diacetyl and 2,3-Pentanedione
  • Esters
  • Fatty Acids
  • Higher Alcohols
  • Nitrogen Compounds
  • Organic Acids
  • Sulfur Compounds
  • Yeast Management
  • Counting Yeast Cells
  • Pitching Rates
  • Preservation of Stock Yeast Culture
  • Yeast Cropping
  • Culture Contamination
  • Yeast Washing
  • Yeast Propagation and Scale-Up
  • Replacing Yeast Cultures
  • Starter Cultures
  • Rehydration of Active Dried Yeast
  • Laboratory Propagation
  • Brewery Propagation
  • Culture Contamination
  • Calculations
  • Piching by Cell Number