Biology - Food Production part 2 (The main stages of yoghurt making ( …
Biology - Food Production part 2
The main stages of yoghurt making
Incubation - Addition of bacterial culture (lactobacillus) and incubated at 37-44°c for 3-6 hours.
Fermentation - The bacteria converts lactose to lactic acid. The pH drops which makes the milk solidify.
Pasteurisation - Of milk, heating it to 72°c for 15 seconds and then cool it rapidly. This kills any active bacterial in the milk.
Cooling - Thickened yoghurt is cooled to about 5°c.
Sterilisation - Using bleach or steam, this kills off unwanted bacteria.
Additions - Flavours and fruits
Sterilise --> Pasteurise milk --> Add lactobacillus bacteria --> Incubate --> Fermentation --> Add fruit.
Main stages in bread production
Make dough by combining yeast with flour, water and some sugar.
The enzymes in the yeast breakdown the flour to release sugars, these are first used in aerobic respiration but the yeast soon runs out of oxygen.
Then the yeast switches to anaerobic respiration and produces lots of CO2 and ethanol.
The dough is left for a few hours for this process (proving) to happen. The dough rises as the CO2 bubbles get trapped. It can get to 4 or 5 times its volume.
The dough is kneaded to mix all the ingredients together and then left somewhere warm.
The dough is then baked in a hot oven. The yeast are killed. The ethanol is evaporated.
The Chemistry of Bread-Making
Flour, Water and Salt
Proteins specifically glutenin and gliadin.
Starch and Sugar
Starch composed of many sugar molecules stuck together by enzymes. It then turns into glucose, this is used by yeast for fermentation.
Yeast and Fermentation
Glucose -> Yeast -> Carbon dioxide or Ethanol. Carbon dioxide helps bread rise. While Ethanol is boiled off during baking.
Fats - Weaken the gluten network, giving softer bread. Also stabilise gas bubbles , increasing loaf volume.
Baking Soda - Sodium Bicarbonate. Combined with moisture and acidity, produces carbon dioxide, which can help bread rise. Can cause bitterness.
Baking powder - Also sodium bicarbonate, but with cream of tartar (potassium bitartrate), an acid ingredient that activates the bicarbonate.
Xanthan Gum - Used in the production of gluten free breads.
How does a Fermenter work?
Water is used to keep the tank cool and at the optimum temperature for growth.
Air pumped in if the organisms respire aerobically.
This motor will then turn the stirring paddles. Which keeps solution agitated (moving).
The culture medium containing the microorganisms and nutrients can now be added.
Special probes measure temperature and pH so that the conditions can be automatically controlled.
The fermenter must first be sterile
They can cause serious disease in humans or they can be used for our benefits.
These are living organisms that can only be seen with the help of microscope.
Conditions inside fermenters need to be controlled.
We don't just use them to make bread and yoghurt but all sorts of products such as penicilin and insulin.
Variables that can be changed: Temperature, mass of yeast, type of yeast, pH, concentration of glucose.
Investigating fermentation (look at sheet)
How can a be controlled in the fermenter
Sterile conditions: Steam is passed through the fermenter between batches to kill microorganisms.
pH: Acid or Alkali can be added once it has been automatically tested.
Oxygen: Air is supplied through the air inlet.
Agitation - Paddles and stirrers mix the culture
Temperature: This is recorded and cool water can be added.
Nutrients: Can be carefully selected and added at an appropriate concentration to the fermenter.
Reason for controlling
Sterile conditions: To ensure pathogenic microorganism that might have found their way into the fermenter cannot reproduce.
pH: Ensure appropriate pH for enzyme function so active sites do not change shape.
Oxygen: Allows aerobic respiration to occur.
Agitation: The microoragnisms are kept in suspension so are surrounded by nutrients and do not settle.
Temperature: So that the appropriate level of kinetic energy for enzyme reactions but not too high that enzymes denature.
Nutrients: Require to allow microorganisms to reproduce and produce desired product.