Yeast Production for Brewery and Baking: Uses of Yeast in Brewery and Bakery Industries – Yeast is one of the essential things needed in the industry especially in Brewery and Baking industries. For drinks and bread for instance to be produced, yeast is mostly added. This article actually treats the uses of yeast production in brewery and baking industry, the enzymes and microorganisms involved.

Yeast Production for Brewery and Baking: Uses of Yeast in Brewery and Bakery Industries

Yeasts are unicellular organisms with some species having the ability to develop multicellular characteristics by forming strings of connected budding cells known as pseudohyphae or false hyphae.

The yeast species Saccharomyces cerevisiae converts carbohydrates to carbon dioxide and alcohols through the process of fermentation. The products of this reaction have been used in baking and the production of alcoholic beverages for thousands of years. S. cerevisiae is also an important model organism in modern cell biology research, and is one of the most thoroughly studied eukaryotic microorganisms. Yeasts have recently been used to generate electricity in microbial fuel cells and to produce ethanol for the biofuel industry.

Mechanism of Yeast Production

Yeasts are heterotrophic organisms in which the energy and carbon metabolism are interconnected and anabolism is coupled to catabolism. Yeasts preferentially metabolize sugars that are converted principally to ethanol and carbon dioxide, but they can utilize different carbon sources, such as amino and organic acids, polyols, alcohols, fatty acids, and other compounds, depending on the species. According to the process utilized to generate energy (respiration and/or fermentation), they can be classified as:

• nonfermentative yeasts with only a respiratory metabolism;
• obligate-fermentative yeasts, only capable of metabolizing glucose through alcoholic fermentation;
• facultative-fermentative yeasts, possessing either a fully respiratory or a fermentative metabolism or even both in a mixed metabolism depending on the growth conditions, the type and concentration of the carbon source, and/or oxygen availability.

Uses of Yeast

The useful physiological properties of yeast have led to their use in the field of biotechnology. Fermentation of sugars by yeast is the oldest and largest application of this technology. Many types of yeasts are used for making many foods: baker’s yeast in bread production, brewer’s yeast in beer fermentation, and yeast in wine fermentation and for xylitol production.

Yeast production for brewery

Alcoholic beverages are defined as beverages that contain ethanol (C₂H₅OH). This ethanol is almost always produced by fermentation – the metabolism of carbohydrates by certain species of yeasts under anaerobic or low-oxygen conditions. Beverages such as mead, wine, beer, or distilled spirits all use yeast at some stage of their production. A distilled beverage is a beverage containing ethanol that has been purified by distillation. Carbohydrate-containing plant material is fermented by yeast, producing a dilute solution of ethanol in the process. Spirits such as whiskey and rum are prepared by distilling these dilute solutions of ethanol. Components other than ethanol are collected in the condensate, including water, esters, and other alcohols, which (in addition to that provided by the oak in which it may be aged) account for the flavour of the beverage.

Beer

Brewing yeasts may be classed as “top-cropping” (or “top-fermenting”) and “bottom-cropping” (or “bottom-fermenting”). Top-cropping yeasts are so called because they form a foam at the top of the wort during fermentation. An example of a top-cropping yeast is Saccharomyces cerevisiae, sometimes called an “ale yeast”. Bottom-cropping yeasts are typically used to produce lager-type beers, though they can also produce ale-type beers. These yeasts ferment well at low temperatures. An example of bottom-cropping yeast is Saccharomyces pastorianus, formerly known as S. carlsbergensis.

Wine

Yeast is used in winemaking, where it converts the sugars present (glucose and fructose) in grape juice (must) into ethanol. Yeast is normally already present on grape skins. Most added wine yeasts are strains of S. cerevisiae, though not all strains of the species are suitable. Different S. cerevisiae yeast strains have differing physiological and fermentative properties, therefore the actual strain of yeast selected can have a direct impact on the finished wine. Significant research has been undertaken into the development of novel wine yeast strains that produce atypical flavour profiles or increased complexity in wines.

Yeast production for baking

Yeast, the most common one being S. cerevisiae, is used in baking as a leavening agent, where it converts the food/fermentable sugars present in dough into the gas carbon dioxide. This causes the dough to expand or rise as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets “set”, giving the baked product a soft and spongy texture. The use of potatoes, water from potato boiling, eggs, or sugar in a bread dough accelerates the growth of yeasts. Most yeasts used in baking are of the same species common in alcoholic fermentation. In addition, Saccharomyces exiguus (also known as S. minor), a wild yeast found on plants, fruits, and grains, is occasionally used for baking. In breadmaking, the yeast initially respires aerobically, producing carbon dioxide and water. When the oxygen is depleted, fermentation begins, producing ethanol as a waste product; however, this evaporates during baking.

When yeast is used for making bread, it is mixed with flour, salt, and warm water or milk. The dough is kneaded until it is smooth, and then left to rise, sometimes until it has doubled in size. The dough is then shaped into loaves. Some bread doughs are knocked back after one rising and left to rise again (this is called dough proofing) and then baked. A longer rising time gives a better flavor, but the yeast can fail to raise the bread in the final stages if it is left for too long initially.