Yeast in the Animal Feed Industry

 By Joseph W. Ward, Ph.D

 Part 1: Practical Guide to Common Terminology of Yeast Products
This is part one of a three-part series to serve as a practical guide to provide a semi-technical and non-technical understanding of yeast and/or yeast components that are used in the animal feed industry.  Part I is a practical guide to common terminology of yeast products available to the animal feed industry.  Part II will cover a brief overview of the history of yeast, the structure of yeast and yeast production.  Part III will describe how yeast is used in the animal feeding industry and insights of the mechanisms of how the feeding of yeast or yeast components to animals enhances animal production and health.
Listed below are common terms that are used in the animal feed industry:
Primary Dried Yeast or Dried Yeast is the dried, non-viable yeast of the botanical classification Saccharomyces cerevisiae which has been separated from the medium it was grown on (propagated). It must consist of yeast cells with no fillers and contain not less than  40% crude protein.  Crude Protein and dry matter percentage are declared and listed as a guaranteed on the feed label.    
Active Dry Yeast is yeast which has been dried in such a manner as to preserve yeast viability.  It must contain no added cereal or filler and must contain live yeast cells.  Live yeast cells per gram are declared and listed as a guarantee on the feed label.
Coated Active Dry Yeast is yeast which has been dried in such a manner as to preserve yeast viability.  Specific drying processes and/or additional coating technologies may be used to protect the live yeast cells during feed production processes, making them specifically adapted for pelleted feeds.  It may contain added cereal, filler and/or coating material and must contain live yeast cells per gram.  Added cereal, filler and/or coating material are typically declared in the ingredient section of the label.  Live yeast cells per gram are declared and listed as a guarantee on the label.
Irradiated Dried Yeast is the dried, non-viable yeast which has been subjected to ultraviolet rays in order to produce anti-rachitic (curing or prevention rickets) potency (commonly described as Vitamin D).  When Irradiated Dried Yeast is used as an ingredient of proprietary feeds for four-footed animals, the name may be followed by a parenthetical phrase (Source of Vitamin D2). When listed as a source of Vitamin D2, the activity is declared and listed as a guarantee on the feed label.
Brewers Dried Yeast is the dried, non-viable, non-extracted yeast of the botanical classification Saccharomyces resulting as a by-product from the brewing of beer and ale. It contains not less than 35% crude protein. The crude protein content is guaranteed on the feed label.
Grain Distillers Dried Yeast is the dried, non-viable yeast of the botanical classification Saccharomyces resulting from the fermentation of grains and yeast, separated from the mash, either before or after distillation. It contains not less than 40% crude protein.
Torula Dried Yeast or Candida dried yeast is the dried non-fermented yeast of the botanical classification (torulopsis) Candida utilis (formerly Torulopsis utilis) which has been separated from the medium in which it is propagated. It contains not less than 40% crude protein.
Yeast Culture is the dried product composed of yeast (Saccharomyces cerevisiae and/or Kluyveromyces marxianus), the medium on which it was grown, and the metabolic and/or nutritional products produced by the yeast.  Dried in such a manner as to preserve the fermented products produced by the yeast but not as a source of live or viable yeast cells.  There is no reference to media in main ingredient listing is not required when yeast culture forms a component of a proprietary mixed feed.
Molasses Yeast Condensed Solubles are produced into a syrup consistency by condensing the broth that remains after the removal of baker’s yeast cells that have been propagated (grown) on molasses.
is the non-viable, non-extracted yeast of the botanical classification Saccharomyces resulting as a by-product from the brewing of beer and ale. It contains not less than 35% crude protein on a dry weight basis. The guaranteed analysis on the feed label lists the maximum moisture percentage.
Yeast Extract is the concentrated water soluble fraction of yeast cells obtained from either mechanical rupture of the cells or after autolysis of the yeast.  It is separated from the yeast cell wall from a selected strain of yeast, Saccharomyces cerevisiae.  It contains mainly proteins and nucleotides.  It may be dried or concentrated.  On a dry matter basis, it contains not less than 35% crude protein.  Salts may be added.  Dry matter and salt percentages are declared and listed as a guaranteed on the label.
Hydrolyzed Yeast is a concentrated, non-extracted, partially soluble, yeast digest solubilization is accomplished by enzymatic hydrolysis of whole Saccharomyces cerevisiae cells. Salts may be added as processing aids in accordance with good manufacturing practice. It contains not less than 35% crude protein.
Molasses Hydrolyzed Yeast is a concentrated, non-extracted, partially soluble yeast digest.  Yeast cells are sourced from the fermentation of molasses.  Solubilization accomplished by enzymatic hydrolysis of whole Saccharomyces cerevisiae cells.  Salt may be added as processing aids in accordance with good manufacturing practice. It contains not less than 30% crude protein.
Yeast Cell Wall is the fraction resulting from the partial separation of the rigid outer polysaccharide layer of yeast.  It is the insoluble fraction of yeast and depending on the separation process may contain a unique percentage and combination of proteins, mannans, beta glucans, glycogen and chitin.
Currently yeast and yeast components are being used in a number of industries that include baking and fermenting, flavoring, human nutrition, plant health, animal health and soil health.  Yeast and yeast components have been fed to animals for hundreds of years.  Although the feeding of yeast has been around a long time there has been renewed interest and better understanding of this micro-biotic technology.  There has been a lot of confusion and misunderstanding throughout the animal feed industry concerning how yeast products and yeast components really benefit and enhance animal performance and health.  Part II will cover a brief overview of the history of yeast, the structure of yeast and yeast production.  Part III will describe how yeast is used in the animal feeding industry and insights of the mechanisms of how feeding yeast and yeast components can enhance animal health and performance.