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YEAST

YEAST. Single Celled fungus (plant) No chlorophyll - cannot produce its own food. Generally feeds on dead organic material. Often seen as a grey dust on foods (like grapes and plums) Needs food and a suitable temperature to grow Multiplies by budding. Yeast – bread making.

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YEAST

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  1. YEAST • Single Celled fungus (plant) • No chlorophyll - cannot produce its own food. • Generally feeds on dead organic material. • Often seen as a grey dust on foods (like grapes and plums) • Needs food and a suitable temperature to grow • Multiplies by budding

  2. Yeast – bread making • Yeast can be white, brown, pink or red • All prefer different temperatures • E.g. pink prefers 20oC • All types respire to release energy to stay alive • Yeast can respire when dried – but very little • When active, release lots of CO2 • Bubbles of CO2 helps bread dough to rise • Heat in the oven then kills the yeast

  3. Beer • Yeast converts sugar into alcohol & CO2 • This is fermentation • Fermenters are used for alcohol production • Beer is made from malt, water, sugar, hops & yeast • Alcohol content depends on: • - type of yeast used • - temperature of fermenter • - fermentation time • Yeast can be top or bottom fermenting

  4. Beer maturing • Beer is matured in a storage container • This develops flavour • Brewery conditioned beer • - stored in large tanks • - yeast removed, and extra CO2 added before packaging • Cask-conditioned beer • - stored in wooden or steel casks • - yeast cells given more sugar, to produce more CO2 • - beer often dark, with a strong flavour

  5. Growing yeast - aseptic • Can be grown on agar gel • Agar gel made from agar powder, nutrients & water • Mixed in a McCartney bottle • All plates, bottles etc sterilised in an autoclave first • Agar gel mixture is then poured into a sterile petri dish • A bunsen is used to sterilise the bottle, and carry any spores upwards

  6. Kefir • Kefir • - alcoholic (2%), fermented milk drink • - a colony of bacteria & yeast added to milk • - lactic acid gives a sour taste • - CO2 gives a slight fizz

  7. Enzymes & Immobilisation • Enzymes are produced by all living cells • Each control a biochemical reaction • Can be removed from cells for industrial processes • Kefir can be made using immobilised enzymes • These are trapped in gel beads • The enzyme (lactase) reacts with the milk • The sugar in the milk (lactose) is broken down

  8. Food flavouring & colouring • Yeast flavours many foods • - soups, snacks, and stock cubes • Pink yeast can also be added to fish feed • This can give fish a pink colour e.g. salmon • This is better than using dyes in food

  9. Environmental impact • Industries often release yeast into rivers • Acts as a food source for bacteria/algae • They grow, and use up all the oxygen in the river • Other river animals die • Yeast can be upgraded • - to make ‘cattle cake’

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