Distillers Yeast

Ethanol (as industrial solvent) and distilled liquors such as whiskey, tequila, rum and brandy are produced by using Distiller s yeast. They are usually isolated from beet or eane molasses and fermented fruits. Distiller s yeast must exhibit certain properties that will influence their selection for industrial use. Some of the prerequisite properties are rapid fermentation, high alcohol yield, high stress tolerance, high alcohol tolerance, low foam formation. 

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The most widely available yeast biomass is a by-product of the brewing industry, where the multiplication of yeast during brewing results in a surplus of ceUs. Eor every barrel (117 L) of beer brewed, 0.2—0.3 kg of yeast soHds may be recovered. In the U.S., a substantial fraction is recovered and made available about 40 x 10 kg of brewers yeast aimually. The yeast is recovered from beer by centrifuging and dried on roUer dmms or spray dryers and sold as animal feed or a pet-food supplement. It can be debittered by alkaline extraction to remove the bitter hop residues, and is then sold mainly by the health-food industry. It is available as tablets, powder, or flakes and is often fortified with additional vitamins. Distillers yeast caimot be readily separated from the fermented mash and the mixture is sold as an animal feed supplement. 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. All distillers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distillation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oils). Naturally occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

Lilly, M., Bauer, F.F., Lambrechts, M.G., Swiegers, J.H., CozzoUno, D. Pretorius, l.S. (2006a). The effect of increased yeast alcohol acetyltransferase and esterase activity on the flavour profile of wine and distillates. Yeast, 23, 641-659. 

In the case of neutral spirits, the intention is to optimally purify the distillate and therefore separate aromatic components, such as fermentation by-products (fusel oils), as much as possible and to ideally obtain absolutely neutral ethyl alcohol. Today s most common raw materials for the production of beverage alcohol are potatoes, grain and molasses. For the fermentation, so-called distillers yeasts, in particular top-fermenting yeast types are used. Since the measures are not sterile and increased temperatures accelerate the fermentation process, the yeast strains must provide good fermentation capabilities such as high resistency against alcohol, acidity and increased temperatures. 

Fermentations—The saccharified wort obtained in the manner described is run into fermenting vessels and treated with yeast to start the fermentation special distilling yeast is used, that is, selected culture yeasts adapted to distilling conditions. If pressed yeast is added about 2 lbs, are employed for everj lOO gallons of wort. Usually, however, a preliminary fermentation is made iu a good malt wort, this provides a culture of vigorous yoimg yeast cells, and is added to the main wort in the proportion of 4 to 5 per cent. 

De Becze, G. I. Reproduction of distillers yeasts. Biotechnol Bioeng 1964,6,191-221. 

The most critical step for production of alcoholic spirits is fermentation. After cooling the wort to 20°C-30°C, a pure strain or a mixture of strains of distillers yeast is pitched to convert fermentable carbohydrates into ethanol, and soluble protein into fusel alcohols and a wide array of metabolites that affect the flavor, aroma, and overall acceptability of the finished distilled product. Most fermentations are carried out with Saccharomyces cereviceae pitched at a rate of approximately 0.5 kg of fresh compressed yeast/hL. Most processes are batch, although there are some modern... 

CHjCOCOOH. A colourless liquid with an odour resembling that of ethanoic acid, m.p. 13 C, b.p. 65 C/lOmm. It is an intermediate in the breakdown of sugars to alcohol by yeast. Prepared by distilling tartaric acid with potassium hydrogen sulphate. Tends 10 polymerize to a solid (m.p. 92 C). Oxidized to oxalic acid or ethanoic acid. Reduced to ( + )-Iactic acid. 

Molasses is also used as an inexpensive source of carbohydrate in various fermentations for the production lactic acid, citric acid, monosodium glutamate, lysine, and yeast (60). Blackstrap molasses is used for the production of mm and other distilled spirits. 

Beer. Beer is the alcohoHc product arising from the yeast fermentation of saccharified grain mash. It may or may not include stillage from a previous fermentation/distillation (see Beer). 

Within each type of distilled spidts, wide vadations of flavor can be achieved by the type and amount of starting grains or other fermentable matedals, methods of preparation, types of yeasts, fermentation conditions, distillation process, maturation time and temperature, blending, and use of new technologies such as membrane separation. 

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