Food production by fermentation 20.

Bread production & yeast fermentation

1. make a dough by combining yeast with flour, water and some sugar.

2. the dough is kneaded to mix all the ingredients together and then left somewhere warm.

3. the enzymes in the yeast breakdown the flour to release sugars, these are first used in aerobic respiration, but the yeast soon run out of oxygen.

4. then the yeast switches to anaerobic respiration and produces lots of CO2 and ethanol.

5. the dough is left for a few hours for this process to happen. the dough rises as the CO2 bubbles get trapped. it can get 4-5 times its volume.

6. the dough is then baked in a hot oven. the yeasts are killed. the ethanol is evaporated.

Yoghurt production

1. Sterilisation of the equipment using bleach or steam.

2. Pasteurisation of milk —heating it to 70°C for 15s to kill microorganisms and then cooling it rapidly.

3. Incubation: addition of bacterial culture (lactic acid bacteria e.g. lactobacillus bulgaricus) and incubated at 37°C—44°C for 3-6h.

4. Fermentation: the bacteria convert lactose to lactic acid (by anaerobic respiration, lactose = galactose + glucose). the pH drops which coagulates the milk protein, makes it thicker (and in this acid environment the other bacteria do not grow).

5. Cooling: thickened yoghurt is cooled to about 5°C to prevent it from spoiling.

6. Addition: flavours and fruits can be added.

Fermenter

• Big tanks that contain large amount of liquid culture of organisms, where the conditions are kept in perfect optimum levels for growth.

• the fermenter must first be made sterile by pumping steam through the equipment at high pressure.

• the culture medium containing microorganisms and nutrients can now be added

• the motor will then turn the stirring pedals, keeping the solution agitated.

• the tank is surrounded by a water jacket that keeps the tank cool and at the optimum temperature for growth.

• there is also a pipe for pumping the air in.

• the special probs can measure temperature and pH so that the conditions can be automatically controlled.

..

..