7.2 - Using micro-organisms to produce food
Fermentation
● Processes carried out by micro-organisms, e.g.: bacteria/fungi
● Yeast - production of bread
○ Yeast - unicellular fungus (i.e.: can carry out BOTH aerobic & anaerobic)
○ When production of bread, carries out anaerobic respiration:
C6H12O6 → 2CO2 + 2C2H5OH (+ energy)
glucose → carbon dioxide + ethanol (+ energy)
○ Main ingredients of bread:
■ (Wheat [小麥]) flour — “Further sugars are released from
enzymatic breakdown of starch in the bread flour, allowing
the yeast to continue to respire anaerobically.”
■ Water
■ Yeast — produces CO2, making bread rise (process known as
proving [打樣])
■ Sugar — glucose - food for yeast
■ Salt
■ (a little) Fat/oil
○ Mixing process known as kneading (揉捏) — ensures all yeast cells
evenly spread throughout dough
○ Conditions:
■ 25˚C (when fermenting)
■ 230˚C (when baking - for ~15 mins)
○ ***In the end, ethanol produced by yeast evaporates, yeast killed by high
temperature in baking environment
Production of yoghurt - from milk
● ***Purpose: extending food\milk shelf life
Lactobacillus (bulgaricus)
● ***lactose (乳糖)(sugar found ∈milk )→ lactic acid( 乳酸)
● During fermentation:
○ Bacterial starter culture (including Lactobacillus) added to milk
○ Milk THEN kept 37~44˚C for 3~6 hrs
● As lactic acid produced, pH falls; ↑ acidity makes milk protein coagulate (凝)
○ Acidity also helps prevent growth of other (potentially harmful) micro-
organisms
● Towards end of process, fruit/other flavourings can be added to yoghurt
○ Different milks can be used (including skimmed [脫脂]/dried milk [奶
粉]//milk from different mammals)
1
Fermentation
● Processes carried out by micro-organisms, e.g.: bacteria/fungi
● Yeast - production of bread
○ Yeast - unicellular fungus (i.e.: can carry out BOTH aerobic & anaerobic)
○ When production of bread, carries out anaerobic respiration:
C6H12O6 → 2CO2 + 2C2H5OH (+ energy)
glucose → carbon dioxide + ethanol (+ energy)
○ Main ingredients of bread:
■ (Wheat [小麥]) flour — “Further sugars are released from
enzymatic breakdown of starch in the bread flour, allowing
the yeast to continue to respire anaerobically.”
■ Water
■ Yeast — produces CO2, making bread rise (process known as
proving [打樣])
■ Sugar — glucose - food for yeast
■ Salt
■ (a little) Fat/oil
○ Mixing process known as kneading (揉捏) — ensures all yeast cells
evenly spread throughout dough
○ Conditions:
■ 25˚C (when fermenting)
■ 230˚C (when baking - for ~15 mins)
○ ***In the end, ethanol produced by yeast evaporates, yeast killed by high
temperature in baking environment
Production of yoghurt - from milk
● ***Purpose: extending food\milk shelf life
Lactobacillus (bulgaricus)
● ***lactose (乳糖)(sugar found ∈milk )→ lactic acid( 乳酸)
● During fermentation:
○ Bacterial starter culture (including Lactobacillus) added to milk
○ Milk THEN kept 37~44˚C for 3~6 hrs
● As lactic acid produced, pH falls; ↑ acidity makes milk protein coagulate (凝)
○ Acidity also helps prevent growth of other (potentially harmful) micro-
organisms
● Towards end of process, fruit/other flavourings can be added to yoghurt
○ Different milks can be used (including skimmed [脫脂]/dried milk [奶
粉]//milk from different mammals)
1
