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Biotechnology. Living Factories. G Davidson. Yeast at Work. Yeast is a tiny living thing. It is called a microbe. It is used in baking and brewing. Yeast at Work. Yeast makes many useful products. E.g. yeast can break down glucose into carbon dioxide and ethanol (alcohol).
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Biotechnology Living Factories G Davidson
Yeast at Work • Yeast is a tiny living thing. • It is called a microbe. • It is used in baking and brewing. G Davidson
Yeast at Work • Yeast makes many useful products. • E.g. yeast can break down glucose into carbon dioxide and ethanol (alcohol). • This is called fermentation. • Yeast obtains energy by doing this. G Davidson
Yeast Cells G Davidson
Simple Fermenters • A fermenter is a vessel which can be used to manufacture a range of products in the presence or absence of oxygen. • Yeast can be used to ferment sugars to produce many useful substances for man. G Davidson
Simple Fermenter G Davidson
Large Fermenters G Davidson
Brewing • Wild yeasts are to be found on most fruits, seeds and flowers. • Long ago people found that when they stored fruits, seeds and flowers in water, new liquids were made. • These were called wine and beer. G Davidson
Brewing • The wild yeasts were responsible for this. • Today, only particular strains of yeast are used in brewing and wine-making. • To make beer which can be sold to the public, commercial brewers must give the yeast the best growing conditions. G Davidson
Taking Care of Yeast • Living yeast is used in fermentation. • It usually works best at temperatures between 10oC – 18oC and a pH of about 7. G Davidson
Taking Care of Yeast • Given these conditions, a controlled supply of oxygen and sugar as food, yeast will grow well. • It is also important that unwanted microbes are kept out. G Davidson
Starch & Germination • Starch is present in barley grains. • This starch cannot be used by yeast as a food. • First of all brewers must germinate the barley. • Barley grains contain enzymes. • Germination allows the enzymes in the barley to act on the starch. G Davidson
How Yoghurt is Made G Davidson
How Yoghurt is Made • Milk can be changed into cheese and yoghurt. • This preserves milk. • People have done this for hundreds of years. G Davidson
How Yoghurt is Made • Certain bacteria are used in this process. • Two strains of bacteria are used to make yoghurt. • They ferment the milk sugar (lactose) into lactic acid. • This acid makes the milk curdle and go lumpy and gives yoghurt its sour taste. G Davidson
Cheese Making G Davidson
How Cheese is Made • Bacteria are added to the milk to make it go sour. • Next an enzyme called rennin is added. • This breaks down the proteins in milk and forms the solid curd. G Davidson
How Cheese is Made • The liquid whey is then drained off. • The curd is finally allowed to ripen and mature to form cheese. • Some cheeses are then flavoured by adding different microbes. G Davidson
Cheese Making G Davidson
Souring of Milk • Bacteria and sugar are present in fresh milk. • The bacteria can feed on the sugar and cause milk to sour. • The souring of milk is a fermentation process. G Davidson
Malting • Nowadays the brewing of beer, which involves malting and batch processing, is carefully controlled using modern scientific methods. • Malting changes the starch in barley into sugars which can be fermented by yeast. • The whole process takes 7-8 days and is carried out in the maltings building. G Davidson
Malting • First the barley is soaked; this is called steeping. • Extra water is then removed and the grain is turned regularly to allow aeration. G Davidson
Malting • At this stage the temperature is carefully controlled to regulate germination of the grain. • When germination begins, enzymes in the grain break down the starch into maltose. • During the brewing process the maltose is converted into fermentable sugars. G Davidson
Maltings Building G Davidson
Batch Processing • This is the technique used by commercial brewers to provide the best conditions for fermentation. • The common feature of all batch processes is that they involve closed systems. • After the addition of the raw materials, nutrients and yeast culture, the system is left untouched, although controlled, until fermentation ends. G Davidson
Batch Processing • The beer is then removed. • Fermentation ends because nutrients run out or waste materials build up. • The growth rate of the yeast is therefore higher at the start, falling to zero at the end. • Batch processing which is monitored and controlled to give optimum conditions maximises the quality and quantity of the beer. G Davidson