YEASTYEAST Single Celled fungus (plant)Single Celled fungus (plant) No chlorophyll - cannot No chlorophyll - cannot
produce its own food.produce its own food. Generally feeds on dead Generally feeds on dead
organic material. organic material. Often seen as a grey dust Often seen as a grey dust
on foods (like grapes and on foods (like grapes and plums)plums)
Needs food and a suitable Needs food and a suitable temperature to growtemperature to grow
Multiplies by buddingMultiplies by budding
Yeast – bread makingYeast – bread making Yeast can be white, brown, pink Yeast can be white, brown, pink
or redor red All prefer different temperaturesAll prefer different temperatures E.g. pink prefers 20E.g. pink prefers 20ooCC All types respire to release All types respire to release
energy to stay aliveenergy to stay alive Yeast can respire when dried – Yeast can respire when dried –
but very littlebut very little When active, release lots of COWhen active, release lots of CO22
Bubbles of COBubbles of CO22 helps bread helps bread dough to risedough to rise
Heat in the oven then kills the Heat in the oven then kills the yeastyeast
Beer Beer Yeast converts sugar into Yeast converts sugar into
alcohol & COalcohol & CO22
This is This is fermentationfermentation Fermenters are used for Fermenters are used for
alcohol productionalcohol production Beer is made from malt, Beer is made from malt,
water, sugar, hops & yeastwater, sugar, hops & yeast Alcohol content depends Alcohol content depends
on:on: - type of yeast used- type of yeast used - temperature of fermenter- temperature of fermenter - fermentation time- fermentation time Yeast can be top or bottom Yeast can be top or bottom
fermentingfermenting
Beer maturingBeer maturing Beer is matured in a storage Beer is matured in a storage
containercontainer This develops flavourThis develops flavour Brewery conditioned beerBrewery conditioned beer - stored in large tanks- stored in large tanks - yeast removed, and extra CO- yeast removed, and extra CO22
added before packagingadded before packaging Cask-conditioned beerCask-conditioned beer - stored in wooden or steel casks- stored in wooden or steel casks - yeast cells given more sugar, - yeast cells given more sugar,
to produce more COto produce more CO22
- beer often dark, with a strong - beer often dark, with a strong flavourflavour
Growing yeast - Growing yeast - asepticaseptic
Can be grown on agar gelCan be grown on agar gel Agar gel made from agar Agar gel made from agar
powder, nutrients & waterpowder, nutrients & water Mixed in a McCartney Mixed in a McCartney
bottlebottle All plates, bottles etc All plates, bottles etc
sterilised in an sterilised in an autoclaveautoclave firstfirst
Agar gel mixture is then Agar gel mixture is then poured into a sterile petri poured into a sterile petri dishdish
A bunsen is used to A bunsen is used to sterilise the bottle, and sterilise the bottle, and carry any spores upwardscarry any spores upwards
KefirKefir
KefirKefir - alcoholic (2%), fermented - alcoholic (2%), fermented
milk drink milk drink - a colony of bacteria & yeast - a colony of bacteria & yeast
added to milkadded to milk - lactic acid gives a sour - lactic acid gives a sour
tastetaste - CO- CO22 gives a slight fizz gives a slight fizz
Enzymes & ImmobilisationEnzymes & Immobilisation Enzymes are produced by all Enzymes are produced by all
living cellsliving cells Each control a biochemical Each control a biochemical
reactionreaction Can be removed from cells Can be removed from cells
for industrial processesfor industrial processes Kefir can be made using Kefir can be made using
immobilised immobilised enzymesenzymes These are trapped in gel These are trapped in gel
beadsbeads The enzyme (lactase) reacts The enzyme (lactase) reacts
with the milkwith the milk The sugar in the milk The sugar in the milk
(lactose) is broken down(lactose) is broken down
Food flavouring & Food flavouring & colouringcolouring
Yeast flavours many Yeast flavours many foodsfoods
- soups, snacks, and - soups, snacks, and stock cubesstock cubes
Pink yeast can also be Pink yeast can also be added to fish feedadded to fish feed
This can give fish a pink This can give fish a pink colour e.g. salmoncolour e.g. salmon
This is better than using This is better than using dyes in fooddyes in food
Environmental impactEnvironmental impact Industries often release Industries often release
yeast into riversyeast into rivers Acts as a food source for Acts as a food source for
bacteria/algaebacteria/algae They grow, and use up They grow, and use up
all the oxygen in the all the oxygen in the riverriver
Other river animals dieOther river animals die Yeast can be Yeast can be upgradedupgraded - to make ‘cattle cake’- to make ‘cattle cake’