Cropping, yeast

Most current commercial ethanol production is from the fermentation of sugar and starch crops. Yeast can rapidly convert sucrose to ethanol with a theoretical carbon conversion of 67%. The production of ethanol from corn grew to about 1.9 billion gallons in 2001. This accounted for 90% of the total ethanol production and an estimated 615 million bushels of corn (6.2% of total corn produced) were consumed. The remaining 10% of ethanol production was by fermentation of grain sorghum, barley, wheat, cheese whey, and potatoes. 

It has already been discussed that a major difference between brewer s yeast strains and other alcoholic producing yeasts is that brewers recycle their yeast cultures from one fermentation into a subsequent fermentation. It is therefore important to protect the quality of the cropped yeast culture because it will be used to pitch a later fermentation and will consequently have a profound effect on the quality of the resulting beer produced with it. Distillers (e.g. Scotch whisky producers) use a yeast culture only once. This introduces a separate series of selection criteria for a yeast culture that are beyond the scope of this chapter. 

If a cropped yeast culture is not stored properly, cell consistency will suffer, and it will adversely affect fermentation and beer quality. After cropping, the yeast is stored in a room that is conveniently sanitized and contains a plentiful supply of sterile water and a separate filtered air supply with positive pressure to prevent the entry of contaminants at a temperature of 0°C. Alternatively, insulated tanks in a dehumidified room can be used. In addition, off the shelf yeast storage facilities are available at various working capacities. 

During most of the fermentation ethanol production procedures, a yeast culture is used only once for a single fermentation cycle. However, in brewing, the yeast culture is harvested at the end of a fermentation for reuse in a subsequent fermentation. Between fermentations, the cropped yeast is normally stored before being repitched. As a consequence of this procedure, the yeast culture must be carefully managed between fermentations to maintain its quality. The steps in this yeast management procedure have been discussed in this chapter. 

Alcoholic Fermentation. Certain types of starchy biomass such as com and high sugar crops are readily converted to ethanol under anaerobic fermentation conditions ia the presence of specific yeasts Saccharomyces cerevisia and other organisms (Fig. 6). However, alcohoHc fermentation of other types of biomass, such as wood and municipal wastes that contain high concentrations of cellulose, can be performed ia high yield only after the ceUulosics are converted to sugar concentrates by acid- or enzyme-catalyzed hydrolysis ... 

Ammonium sulfate occurs in trace concentrations in the upper atmosphere. It is widely used as a fertilizer for rice and other crops. It is a source of sulfur for the soil. It is also used as an additive to supply nutrient nitrogen in fermentation processes (e.g., yeast production from molasses). It also is used for fireproofing timber and plastics, and in treatment of hides, and leather production. 

Yeast used to leaven bread and make beer and wine Moldy soybean curds used to treat boils (first antibiotic) Crops and livestock domesticated Powdered chrysanthemums used as first insecticide Microscope invented... 

Ethanol (ethyl alcohol) can be produced from a wide variety of feedstocks, including wood, wastepaper, and crop residues. Ethanol produced from plant biomass is also known as bioethanol. The production of bioethanol from plant biomass involves the fermentation of pulped, mashed, or juiced plant material by yeasts and bacteria (Wiselogel et al., 1996). 

Because of the need for additional sources of nutrients and the constraints on conventional crop production, it is expedient to develop supplementary sources of food protein, e.g. yeast protein. The most popular yeasts belong to the general Saccharo-myces and Candida because of their long tradition of use in foods. 

Insecticides tend to persist longer in soils of high organic matter. In fact, in muck soils (50% or more organic matter), residues have been found bound to soil particles to such an extent that the same amount of toxicant is less effective in muck soil as compared with a sandy type. It has been noted that pesticides are absorbed into crops most readily from sandy soils and least from muck soils. Moisture enhances the release of volatile pesticides from soil particles and also influences the breakdown of other toxicants. Microbial attack has been found to oxidize aldrin to dieldrin, and parathion in the presence of yeast is reduced to the nontoxic aminoparathion in soil. As might be expected, increased soil temperatures can dramatically increase the rate of pesticide loss owing to volatilization and increased breakdown. Cover crops, such as alfalfa, can decrease pesticide volatility from soil whereas cultivation... 

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