Living Factories

BiotechnologySG Biology

Learning Outcomes 1• State that the raising of dough and the

manufacture of beer and wine depend on the activities of yeast.

• Identify yeast as a single celled fungus, which can use sugar as food

• Using a word equation, state the process of fermentation of glucose by yeast.

• Describe the process of anaerobic respiration and compare it with aerobic respiration

Biotechnology• Biotechnology is the use of microbes

and raw materials to produce useful substances.

Biotechnology

Raw materials

Suitable micro-organisms

Biotechnological process

ServicesSewage treatment

Water purification

ProductsFood, enzymes

Fuels

Anti-biotics, hormones

Products of Biotechnology

Structure of Yeast

• Yeast is a single celled fungus

• It multiplies by budding

Yeast

• Yeast breaks down glucose into carbon dioxide and ethanol.– In bread making, the carbon dioxide

helps the bread to rise.– In brewing, the yeast turns sugars into

alcohol.

• Present on fruits, such as grapes as a bloom (grey dust).

Fermentation in Yeast

• Fermentation is respiration in the absence of oxygen (anaerobic respiration).

• It can be represented by an equation.

Glucose carbon dioxide + ethanol + energy

Stages in Bread making

• Add yeast to a warm sugar solution and allow to grow and produce bubbles.

• Add a pinch of salt to the flour• Mix together into a dough• Leave mixture in a warm place covered

by a cloth• Yeast releases CO2 bubbles making

dough rise• Bake dough in a hot oven• Yum Yum

Baking• Yeast is added to , and

.• is made which is folded and

left in a warm place.• (anaerobic respiration)

causes the yeast to produce ethanol and carbon dioxide.

• The causes the dough to rise.• The dough is then baked in the oven which kills

the yeast and removes the .• After baking the bread is ready.

Stages in wine making

• Crush grapes to release juice• Filter juice into fermentation tank• Add yeast to grape juice• Yeast grows using sugar and changes it

into alcohol (CO2 is allowed to escape)

• Alcohol becomes concentrated and kills the yeast

• Wine siphoned into bottles

Wine making• are crushed and the

grape juice is filtered off.• is added to the grape juice.• takes place, yeast uses the

sugar in the grape juice to make and .

• The is allowed to escape.• As the builds up it kills the

yeast.• The wine is removed into bottles and

allowed to .

Learning Outcomes 2

• Describe how commercial brewers provide the best growing conditions for yeast.

• Explain what is meant by the term “batch processing”

• Explain the need for malting of barley before use by the brewing industry.

Growing conditions for Yeast• Food supply– Starch is converted to sugar for yeast

by germinating barley grains on the floor of the malting house (malting)

• Suitable temperature– Optimum temperature maintained in

fermenter vessel by a thermostat• Lack of competition– Other microorganisms killed by

boiling in the wort kettle

Brewing

• A brewer is interested in both the alcohol and the carbon dioxide made by the yeast. – Beer is expected to be alcoholic– the carbon dioxide gives the

characteristic fizz.

Brewing

• Raw materials– Barley grains– Water– Extra sugar– Hops– Live yeast

• By products– Cattle food– Fertiliser– Yeast extract

Brewing (1)• Barely grains which are full of

, which is a large molecule that yeast can not digest

• Barley grains are allowed to germinate.– Starch is converted to sugar.

This is called .• Yeast is added and takes

place.

Brewing (2)• Yeast changes the maltose into

carbon dioxide and ethanol.• As the level builds up the

yeast is killed.• Beer is then made and allowed to

.• To brew the best beer the brewer

must make sure his fermenter vessels are _ and that he uses the

temperature for the yeast.

Learning Outcomes 3

• State that the manufacture of cheese and yoghurt depends on the activity of bacteria.

• State that the souring of milk is a fermentation process.

• Explain the souring of milk in terms of bacterial fermentation of lactose.

Fermentation of Lactose

• When the bacteria growing in milk respire anaerobically, they use the milk sugar lactose as food.

Lactose lactic acid

• This is called lactic acid fermentation

pH7

6

5

4

Days

1 2 3 4 5 6

Souring of milk

• Bacteria feeds on lactose producing lactic acid.

• Milk becomes more acid and its pH falls.

Cheese and yoghurt production

• Lactic acid makes milk curdle• Special strains of bacteria are used

in fermentation in curdling milk.

Flow diagram for the manufacture of yoghurt

Bulk raw milk pasteurisationcooler Incubation at

42oC for 6 – 8 hours

Chiller 5oC

PackagingCool

Storage4oC

Cheese and yoghurt• Cheese– Bacteria added– Milk curdles– Rennin (enzyme) used to

separate milk into curds and whey

– Whey run off– Curds cut into blocks

and mixed with salt to slow bacterial growth

– Packed into moulds

• Yoghurt– Bacteria

added to pasteurised milk

– Milk clots– Yoghurt

formed– Put into tubs

and stored in fridge