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Useful Microorganisms – Revision Pack (B6) Yoghurt Making: The type of bacteria used in yoghurt-making is Lactobacillus. This causes the breakdown of lactose in the milk to lactic acid – this is why yoghurt tastes acidic. Fermentation: STEP 1 – sugar is extracting by crushing grapes (wine) or from barley grains (beer) STEP 2 – The yeast is added STEP 3 – It is kept warm to allow it to ferment – air and other organisms are kept out STEP 4 – The wine/beer is them allowed to clarify (clear); then the clear liquid is drawn off (or removed from the yeast sediment) STEP 5 – The wine/beer may then be pasteurised and then bottled The yoghurt-making process uses bacteria and works using the following steps: STEP 1 – Firstly, the equipment is sterilised STEP 2 – Then milk is pasteurised by heating it to about 78 o C STEP 3 – When the milk has cooled, it is incubated with a culture of bacteria STEP 4 – This is followed by sampling, adding The process of fermentation using yeast involves anaerobic respiration; the word and balanced symbol equations for this are: Glucose (sugar) Ethanol (alcohol) + Carbon Dioxide C 6 H 12 O 6 2C 2 H 5 OH + 2CO 2 The concentration of alcohol made by fermentation is limited, so to make drinks with higher concentrations like whiskey or brandy, the process of distillation is used. This increases the alcohol concentration but is

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Page 1: Web viewThe type of bacteria used in yoghurt ... The process of fermentation using yeast involves anaerobic respiration; the word and balanced symbol

Useful Microorganisms – Revision Pack (B6)

Yoghurt Making:

The type of bacteria used in yoghurt-making is Lactobacillus. This causes the breakdown of lactose in the milk to lactic acid – this is why yoghurt tastes acidic.

Fermentation:

STEP 1 – sugar is extracting by crushing grapes (wine) or from barley grains (beer)

STEP 2 – The yeast is added

STEP 3 – It is kept warm to allow it to ferment – air and other organisms are kept out

STEP 4 – The wine/beer is them allowed to clarify (clear); then the clear liquid is drawn off (or removed from the yeast sediment)

STEP 5 – The wine/beer may then be pasteurised and then bottled

The yoghurt-making process uses bacteria and works using the following steps:

STEP 1 – Firstly, the equipment is sterilised

STEP 2 – Then milk is pasteurised by heating it to about 78oC

STEP 3 – When the milk has cooled, it is incubated with a culture of bacteria

STEP 4 – This is followed by sampling, adding flavours (e.g. strawberry) and packaged

The process of fermentation using yeast involves anaerobic respiration; the word and balanced symbol equations for this are:

Glucose (sugar) Ethanol (alcohol) + Carbon Dioxide

C6H12O6 2C2H5OH + 2CO2

The concentration of alcohol made by fermentation is limited, so to make drinks with higher concentrations like whiskey or brandy, the process of distillation is used. This increases the alcohol concentration but is ONLY allowed on licensed premises, unlike fermentation (using yeast) which you can do at home to make beers or wines using the following steps:

Page 2: Web viewThe type of bacteria used in yoghurt ... The process of fermentation using yeast involves anaerobic respiration; the word and balanced symbol

Useful Microorganisms – Revision Pack (B6)

When yeast is brewing, it soon uses up all of the oxygen available and respires aerobically – this allows the number of cells to increase rapidly. Then the conditions turn anaerobic and this is when the alcohol is made.

Yeast breaks down sugar at different rates depending on the conditions (e.g. temperature and oxygen availability) – you may be asked to interpret graphs on this.

The process of pasteurisation is used to kill any harmful microbes – in this process; the liquid is kept at an elevated temperature for a predetermined amount of time. The temperature and time is dependent on the drink being brewed.

The alcohol concentration generated by fermentation is fairly limited – this is because alcohol at higher concentrations would kill the yeast cells – however, there are some yeast cells which are more resistant to alcohol than others.