Brewers Yeast
(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). Top fermenting yeasts produce beers that are more estery, fruity, and sometimes malty, whereas bottom-fermenting yeasts give beers a characteristic sulphurous aroma. Some other notable differences also include fermentation temperatures and flocculation characteristics. Top-fermenting yeasts are used for brewing ales, porters, stouts, Altbier, Kolsch while bottom-fermenting yeasts are used for brewing lagers such as Pilsners, Dortmunders, Marzen, and Bocks are fermented with bottom-fermenting yeasts.
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Topics Within This Chapter:
- Ale Yeast
- Lager Yeast
- Yeast Life Cycle During the Beer Brewing Process
- The Lag Phase
- The Growth Phase
- The Fermentation Phase
- The Sedimentation Phase
- Yeast Nutritional Requirements in Brewing Beer
- Carbohydrates
- Nitrogen
- Vitamins
- Minerals
- Yeast Byproducts in Brewing Beer
- Esters
- Diacetyl and 2,3-Pentanedione
- Acetaldehydes
- Organic and Inorganic Sulfur Volatiles
- Dimethyl Sulfide
- Fusel Alcohols
- Organic Acids
- Fatty Acids
- Nitrogen Compounds
- Yeast Strain Selection in Brewing Beer
- Rapid Fermentation
- Yeast Stress Tolerance
- Flocculation
- Attenuation
- Beer Flavor
- Good Yeast Storage Characteristics
- Maturation of Yeast
- Degeneration of Yeast
- Pure Culture Maintenance
- Sub-culturing
- Sub-culturing on Agar Slants
- Sub-culturing on Agar Slants with an Oil Overlay
- Desiccation
- Lyophilisation (freeze-drying)
- Freezing in Liquid Nitrogen
- Yeast Propagation and Scale-up
- Laboratory Phase
- Plant Phase
- Aeration
- Optimum Plant Temperatures
- Propagation Plants
- Culture Contamination
- Microscopic Examination
- Yeast Washing
- Distilled or Sterile Water
- Acid Wash
- Acid Wash with Ammonium Persulfate
- Chlorine Dioxide
- Yeast Viability and Replacement in Brewing Beer
- Viability
- Selective Staining
- Standard-Slide Culture Method
- Slide Viability Method
- Fermentation Tests
- Replacement
- Yeast Storage
- Yeast Collection Vessels
- Slurried Storage Systems
- Pressed Cake
- References
