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yeast have been fed to animals for more than a hundred years, either in the form of yeast fermented mash produced on the farm, yeast by products from breweries or distilleries or commercial yeast products specifically produced for a animal feeding. although yeast feeding has been around a long time, there is confusion throughout the industry concerning what the various yeast products readily are.

Yeasts are microscopic fungi- single cell organism which are generally about 5 -10 microns in size. The species differ from each other by where they are found their cellular morphow they reproduce, while they are nearly 50,000 species ofhofogy or shape. how they metabolize different substrates, and fungi there are only 60 different genera of yeast representing about 500 different species.

Yeasts are abundant throughout the environment i.e. water, soil, plants, etc. They can be found cereal grains by product, silages, hays and are even present in the water and soil.

several species have proven very beneficial to man while a few imperfect yeasts are known to be pathogenic. But most yeasts are benign saprophytes and have proven neither useful nor harmful to man or animal.

Very few species of yeasts are used commercially, saccharomyces cerevisiae also known as baker’s yeast is one of the most widely commercialized species. Selected strains of these yeast are used by breweries to make beer and ale, distilleries to make distilled spirits and industrial alcohol, and wineries to make wine, candida utilis [formerly classified as torulopsis utilis] is the yeast known as torula yeast. This yeast is important because it can utilize the pentose sugars from processed wood pulp used to making paper. A third useful yeast is kluyveromyces marxianus. This is the whey yeast which can utilize milk sugar or lactose as a substrate.

Yeast extracts and autolysates are produced from whole yeast cells, either debittered brewer’s yeast, and are used extensively in the food industry for flavour enhancement. Yeast extracts consist of the intracellular components of yeast cell, with the yeast cell wall removed. yeast autolysates consists of ruptured or lysed cells and contain both the intracellular and cell wall fraction both contain 5 nucleotides and glutamate which enhances flavour recognition.

Yeast extract are also used as microbial stimulants in the yeast cell fermentation industries and microbiologist use them in their laboratory growth media to optimize bacterial growth. yeast cell wall remaining as a by -product in the manufacture of yeast extracts are often called yeast hulls or ghosts. They consist predominantly of beta-glucans and mannans, with some chitin and protein. Yeast ghosts are often used in wine making to avoid stuck fermentation due to accumulating octanoic and decanoic acids. These acids are adsorbed onto the ghosts which prevents their inhibitory effect on fermentation.

These yeast products consist of whole yeast cells which have been broken open [lysed] by means of letting the yeast cell destroy itself using own autolytic enzymes [autolysates], by using acids or enzymes to hydrolyse the cell [hydrolysates] or by rupturing the cell using osmotic pressure

They contain both the cell contents and the cell- wall of the cell autolysates are the cleanest of the three types of products because hydrolysates and plasmalysates are generally high in salt or sodium content due to the salt gradients used in plasmalysis or the uses of bases to neutralize the acids used to make hydrolysates

Autolysates are used extensively by the food industry for their ability to enhance food flavours, especially in soups and snack products. The enhancement is due to the yeasts nucleic acid content -the 5nucleotides. The nucleotides add “savoriness” to food by accentuating the effects glutamic acid or monosodium glutamate to enhance flavours.

Yeast extracts consist solely of the intracellular contents of the yeast cell, following lysis of the cell, with the cell wall removed. They are used by microbiologist in the preparation of microbial growth media and by some industrial and pharmaceutical fermentations. Extracts are rich in amino acids, vitamins, and trace minerals and function as growth stimulation for micro-organism.

The yeast cell has a carbohydrate shell around it called the yeast cell wall.it is often called a glucan shield and consists mostly of beta glucans. these are structural polysaccharides [chain of sugar molecules] similar to starch or cellulose. beta -glucans are chains of glucose sugar molecules just like starch, but the sugars are joined together with different linkages [beta-1,3 and 1,6 linkages instead of alpha 1,4 and 1,6 linkages] therefore, different enzymes are needed to break them down in to absorbable sugar molecules. mannans are chains of a different sugar molecule called mannose.