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’