The process of brewing
Brewing is traditional, antique and the oldest microbiological process in use since prehistoric time. It is unique scientific process cum art associated with processing and formation of beverages. Earliest people were unaware about the fact that brewing is carried out strictly by microbes. In microbiology, brewing is anaerobic fermentation consisting complex interactions of microorganism and substrate; the exact mechanism is still unknown. The strains of Saccharomyces, also known as Baker's yeast carry out brewing by fermentation of growth medium which yields products like ethanol, carbon dioxide, acetic acid, glycerol and higher alcohols. Carbohydrates like grains (corn, rice, barley or rye) and fruit juices and pulp (grape, apple, cherry and peach) containing fermentable sugar are principle substrates for production of alcoholic beverages. Two important brewing processes are discussed here.
Production of beer: Beer is made from fermentation of grains. In Europe, America and Orient, beer is produced from barley, maize and rice respectively. Starch is chief grain sugar but is nonfermentable (invert). Therefore, it is first saccharified or hydrolyzed to fermentable forms like maltose or glucose by yeast. There are various ways of starch hydrolysis such as human saliva in Middle East! In Asia, amylase enzyme obtained from fungus Aspergillus oryzae and in Central South America, grains are chewed and spitted into fermentation vessel! There are 5 major steps in the manufacture of beer from barley: malting, mashing, fermenting, maturing and finishing. Barley is soaked and germinated to produce amylase. Such germinated barley is called malt; malted barley is dried and stored for future use. Malting is followed by mashing or grinding of malt. Malt flour is suspended in water to allow hydrolysis of starch. Amylase action hydrolyses starch to maltose, a fermentable sugar. Mixture is boiled at high temperature to stop saccharification process. It is filtered and hops are added to wort (filtrate). Hops are inflorescences of Humulus lupus plant which adds characteristic bitter flavor to beer and also acts as preservative against bacterial growth. Fermentation of hopped wort is initiated by heavy inoculation of yeast. Yeast strains are special and not found naturally like wild yeast. They have been cultured under laboratory conditions and preserved for years especially to carry out fermentation. Fermentation is carried out at low temperature for 5-12 days. Fermented wort is matured at 0˚C for several months to eradicate harsh flavor and undesirable characteristics. During refrigeration, higher alcohols produced undergo spontaneous esterification and oxidation which add desirable characteristics to aging beer. Beer so formed is composed of carbon dioxide, ethyl alcohol, dextrins and proteins, vitamins like riboflavin, ash, and aroma- flavor compounds. Finishing process consists of carbonation, cooling, filtering and dispensing the beer into barrels, cans and bottles. All operations are carried out under aseptic conditions. Bottled and canned beer is pasteurized to kill yeast and other microbes. Beer is produced worldwide employing different or modified fermentation methods. For making beers of higher alcohol content or English ales, top yeasts are utilized. Fermentation is carried out vigorously at higher temperature of 20˚C with rapid evolution of carbon dioxide. In this process growing yeasts are swept to top of fermentation broth. American lager is beer of low alcoholic content. It is produced at low temperature (6-15˚C) with slower carbon dioxide evolution. Yeasts employed are slow fermenters and remain at the bottom during entire fermentation process.
Production of wine: Wine making involves yeast fermentation of glucose and fructose sugars present in fruit juice or pulp. Grapes, peach, banana, apple, orange, berries, cherry and pineapple are fermented to produce wines of different kinds, however grape wines are the most favorite and preferred by people worldover. Fruits are harvested and crushed to yield raw juice (must). Saccharification step is omitted as fruit juice already contains soluble fermentable sugar. It also does not require addition of yeast inoculum as fruit peels naturally bears Saccharomyces cerevisiae var. ellipsoideus yeast hence fermentation is spontaneous. Sometimes, natural yeasts are killed by sulfur dioxide and must is inoculated with desired yeast strains. Wine production proceeds with rise in temperature of fermentation medium which is controlled by consistent cooling otherwise high temperature can kill fermenting yeasts or bring undesired characteristics to resulting wine.
Fermentation process lasts for months or years and during this period wine undergoes spontaneous secondary, tertiary or more fermentation. Spontaneous fermentations are desired as they bring characteristic flavor and aroma to wine and subsequently also reduce unpalatable acidic taste. New wines are clarified by ultrafiltration, stabilized and matured. Red wines are produced from red grapes and red color is extracted from grape skin by alcohol produced in fermentation. Champagne or sparkling wine is produced when bottled/canned wines undergo secondary fermentation under pressure. Sherries are produced in Jerez region of Spanish district. They are fortified wines with 15% alcohol followed by air exposure. Subsequent surface growth of certain yeasts imparts unique sherry flavor to these wines. Dessert or sweet wines are produced from grapes infected with Botrytis cinerea. Fungal infection causes water loss from infected fruits and destruction of malic acid resulting in 'must' of reduced acidity and higher sugar content.
Diseases of beer and wine: Spoilage of alcoholic beverages such as bitterness, disagreeable odor or souring is brought about by microorganisms during storage, maturation or fermentation. Principle spoilage microbes are Pediococcus, Leuconostoc, Lactobacillus, Saccharomyces fermenti, beticus, pasteurianum, Botrytis cinerea and acetic acid bacteria.
Byproducts of brewing: Hard liquors such as gin, whisky, sake, arrak, brandy or rum are obtained by distillation of fermentation broth or ethyl alcohol produced during fermentation process. Large amount of carbon dioxide produced during wine and beer production is recovered and converted to solid form or dry ice. Vinegar of different types is obtained from conversion of ethanol to acetic acid by bacteria from genus Acetobacter. Lactic acid is also obtained from ethanol by lactic acid bacteria. Spent medium is used as animal feed. Fermentation yeast is sold as brewer's yeast for bakery purpose.
Market potential: Ethanol, principle product of brewing is also produced synthetically. There are several critical constrains in microbial production of alcoholic beverages. Despite in detail research studies, interactions between various biological factors in beverage production are still undetermined. Expected product should have desired flavor, aroma, color, taste and sanitation. Type of beverage produced is determined by the nature of plant substrate employed, vigorously growing and alcohol tolerant yeast strains, method of preparation of fermentation medium and operating parameters. Careful monitoring of physical and chemical parameters is of paramount importance and is not required in industrial synthetic alcohol production. Commercial use of synthetically produced ethanol is limited to medical applications and there is never ending demand for wine and beer produced by traditional microbial fermentation process. Both synthetic and commercial processes do not face competition from each other in the ethanol market.
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This article was written to cover the technical aspects of brewing and does not promote its use. Alcohol consumption can be harmful to health, kindly refrain from it or drink responsibly.
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