Milk to curd
A spoonful of curd turns warm milk into curd.
A spoonful of curd
Lukewarm milk with a spoonful of curd is kept in a warm place. Another bowl of the same milk is kept in a cool place.
What will happen after a few hours?
What this lesson covers
The idea
Lactobacillus bacteria feed on milk sugar (lactose), multiply and ferment the milk into curd, producing lactic acid that makes curd sour; they grow well in warm conditions, not cool ones.
A spoonful of curd
Lukewarm milk with a spoonful of curd is kept in a warm place. Another bowl of the same milk is kept in a cool place.
What will happen after a few hours?
- The milk in the warm place turns into curd
- Both bowls stay exactly as milk
- The milk in the cool place turns into curd first
Two bowls of milk
Leave both bowls for a few hours. Then tap each bowl.
Bacteria in the curd
Lactobacillus bacteria feed on the sugar in milk (lactose), multiply and ferment the milk into curd. They produce lactic acid, which makes curd sour. They grow well in warm conditions, so curd forms in a warm place and not in a cool one.
- Compare | Yeast | Lactobacillus
- Kind of microorganism | Fungus | Bacterium
- Makes | Carbon dioxide and a little alcohol | Lactic acid
- Used for | Bread, cakes | Curd
Notes
Lactobacillus bacteria feed on lactose, multiply and ferment milk into curd, producing lactic acid that makes curd sour. They grow well in warm conditions.
Check yourself
What does Lactobacillus feed on in milk?
What makes curd sour?
Why is curd formed in a warm place but not in a cool one?
- Lactose, the sugar in milk — correct. Yes. It feeds on lactose, multiplies and ferments the milk to form curd.
- Salt. Milk is not salty. Lactobacillus feeds on the milk sugar, lactose.
- Sunlight. Lactobacillus is a bacterium that feeds on lactose. It does not use sunlight.
- Lactic acid — correct. Yes. Lactobacillus produces lactic acid instead of alcohol.
- Alcohol. Yeast produces a little alcohol. Lactobacillus produces lactic acid.
- Carbon dioxide. Carbon dioxide forms the bubbles in dough. Curd is sour because of lactic acid.
- Lactobacillus grows well in warm conditions — correct. Yes. In a cool place the bacteria do not grow well.
- Cool milk has no lactose in it. Lactose is in the milk in both places. The bacteria need warmth to grow well.