Introduction:

Usually, the role of yeast from the industrial and technical point of view can't be over emphasized. However most of the genera and species of yeast exist in nature and most of them are employed industrially; most significant are the strains of Saccharomyces cerevisiae. They are employed in the manufacture of beer and wine, and in the leavening of bread. The utilization of yeast as a leavening agent for bread originated in Egypt around 6,000 years ago and spread slowly to the rest of the western world. The invention that alcohol can be distilled and so concentrated originated either in the China or the Arab world.

Wine Production:

Wine production comprised the fermentation of the soluble sugars (that is, fructose and glucose) of the juices of grapes into ethyl alcohol and CO₂. After the grapes are harvested, they are crushed to make a raw juice or must; a highly acidic liquid having 10 to 25 percent sugar by weight in any parts of the world, the mixed yeast flora on the grapes serves up as the inoculums for the fermentation which transform the must into wine. In such a natural fermentation, a complex succession of changes in the yeast population takes place, in the later phases, the true wine yeast Saccharomyces cerevisiae var. ellipsoids predominates.

In California, the must is first treated by sulphur dioxide (SO₂) to eradicate the natural yeast flora; it is then inoculated by the desired strain of wine yeast. Must from both red and white wine grapes (that is, Vitis vinifera) are white and outcomes in a white wine. As the color of red grapes is in the skin, red wines are made up by the fermentation in the presence of the skin, the alcohol developed throughout fermentation extract the color into the wine. Following fermentation the new wine should be categorized, stabilized and aged to generate a satisfactory final product. Such procedures need months and for high quality red wine, even years.

However the high alcohol content and low pH (3.0) of wines make them unfavorable substrates for the growth of most organisms, they are subject to microbial spoilage, particularly when they are exposed to air film-forming yeast and acetic acid bacteria grow at the expenditure of the alcohol, transforming it to acetic acid, this sourcing the wine in the absence of air, lactic acid bacteria grows at the expenditure of residual sugar and impart a 'mousy' taste is the wine. Wine yeast can grow in sweet wines even subsequent to boosting, making the wine become cloudy and less attractive.

Wine spoilage can be avoided either through chemical additives like sulphur dioxide (SO₂) or through sterilization via filtration.

Beer Production:

Beers are produced from grains, like barley, corn and rice; which have no fermentable sugars. The starch of the grams is initially hydrolyzed in the fermentable sugars, glucose and maltose before fermentation by yeast the procedure of hydrolyzing the starch is glucose and maltose is termed as saccharification. Different grains contain diverse saccharification procedures.

In case of barley, starch hydrolyzing enzymes (or amylase) of the grain itself is employed. Barley seeds have little or no amylase, however on germination huge amount of amylase are formed.

Therefore barley is dampened, allowed germinate and is then dried and stored for later use. Such dried, germinated barley termed as malt, is dark in color as an outcome of exposure to increased temperatures throughout drying. The starch of barley remains mainly unaffected by the malting procedure, the first step in beer making is the grinding of malt and its suspension in water let hydrolysis of the starch. When a lighter beer is desired, unmalted barley or sources other cereal grain is added up to the saccharifying mixture. Subsequent to saccharification has reached the desired phase, the mixture is boiled to stop further enzymatic modifications and it is then filtered. Hops are added up to the filtrate (or wort) and contribute a soluble resin that impacts the features bitter flavor of beer and which as well acts as a preservative against the growth of bacteria. After filtration the hopped wort is ready for the fermentation. Special stains of yeast (or Saccharomyces cerevisiae) are employed as inoculum to commence the fermentation procedure that generally takes a period of around 5 to 10 days at low temperature.

Throughout the course of time, special strains of S. cerevisiae having desirable properties have been chosen known as brewer's yeast. Strains of brewer's yeast fall to two groups termed as top and bottom yeast. Top yeast so called as during fermentation they are swept to the top of the vat by the fast evolution of CO₂. They are vital fermenters acting best at relatively high temperature (20%), and are employed for making heavy beers of high alcoholic content like English ales. In contrary, the bottom yeasts are so called as the slower rate of CO₂ evolution lets them to settle to the bottom of the vat throughout fermentation. They are slow fermenters, act preeminent at low temperature (12 to 15 percent), and produce highly low alcoholic content beers such as those made in the United States.

The diseases of beer take place most generally following fermentation either during maturation or following bottling. One agent is a wild yeast Saccharomyces pasteurcarius that impacts a disagreeable bitterness to beer. Spoilage of beer can be prevented by the utilization of pure yeast strains as starters and pasteurization of the final product.

Bread Production:

The yeast employed in bread production belongs to the species Saccharomyces cerevisiae. Till the 19th century, yeast for bread making were obtained directly from the nearby brewery, however nowadays the production of compressed yeast termed baker's yeast is dried under controlled condition which maintain viability of the yeast cells, a treatment which facilitates shipment and storage is employed.

An alcoholic fermentation through yeast is a necessary step in the production of raised breads; this procedure is termed as the leavening of bread.

Throughout bread production, moisturized flour is mixed with yeast and permits to stand in a warm place for some hours. Flour itself includes almost no free sugar to serve up as a substrate for fermentation, however there are some starch splitting enzymes present which produces sufficient sugar fermentation. In the highly refined flours such enzymes have been destroyed, and sugar should be added to the dough, the sugar is quickly fermented by yeast the CO₂ produced is captured in the dough causing it to rise; a procedure termed as leavening while the alcohol produced is driven off throughout the baking procedure.                  

Fungi as a source of protein:

Microorganisms because of their fast growth, high protein content and capability to use organic substrates of slow cost are potentially valuable sources of the animal food. Yeasts are the principal organisms which have been employed and the generic name for the microbial product is single cell protein. The proposed utilization of single cell protein is as a supplement for animal feed to substitute the other main supplements, soya beans and fish meal.

The discovery of Antibiotics:   

The first chemotherapeutically efficient antibiotic was discovered in the year 1929 by Alexander Fleming, a British bacteriologist. He observed that among a pile of petri dishes on his bench one that had been streaked having a culture of Staphylococcus aureus was as well contaminated via a single colony of mould. Though, the colonies instantly surrounding the mould were transparent and appeared to be undergoing lysis. He reasoned that the mould was excreting into the medium a chemical which caused the surrounding colonies to lyse. He isolated the mould that proved to be a species of Penicillium and stabilized that that culture filtrates contained an antibacterial substance which he termed as penicillin.

Penicillin rather of being a single substance, proved to be a class of compounds. These comprise penicillin F, penicillin G, Penicillin V, ampicillin and oxacillin. Since from the year 1945, thousand of different antibiotics generated by fungi, Actinomycetes have been isolated and characterized, for illustration, streptomycin obtained from Streptomyces griseus that is efficient against numerous Gram-positive and Gram-negative and  Mycobacterium tuberculosis was discovered by S. Waksman and A. Schatz. Tetracycline was generated from S. aurefaciens chloramphenicol from S. venezuelae, erythromcin from S. erythreus and cephalosporin from the Cephalosporium spp.

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