What you need:
- Milk - it works best with full fat or semi-skimmed
- Vinegar
- Glass
- Kitchen towel
How to:
1. Pour milk into the glass until its around 1/4 full.
2. Add 2-3 tablespoons of vinegar to the glass. Stir. What can
you see?
3. Place a piece of kitchen towel on top of a second glass.
Slowly pour the mixture through the kitchen paper. You should be
left with a white, plastic-y looking substance in the kitchen towel
and the liquid in the other glass. You might need a few pieces of
kitchen towel to get rid of all the liquid.
What does the white solid look like? Can you squeeze it together
and get rid of more of the liquid? Don't eat it - it won't taste
very nice!
Experiment with milk that contains different amounts of fat.
What happens? What do those mixtures look like?
What's happening:
You've made cheese! Although the stuff you make won't taste very
nice, you've created cheese in a similar way to commercial cheese
makers.
Milk contains a protein called casein, which is negatively
charged. Vinegar contains hydrogen ions, which are positively
charged. The hydrogen ions and casein proteins attract each other
and form the white, plastic-y lumps. The lumps are called curds and
the process of forming the lumps is called curdling. The liquid is
called whey.
Cheese makers don't normally use vinegar to curdle milk - they
normally add an enzyme called rennet, which causes the milk to
separate into curds and whey.
What cheese did your mixture look like? It should look a little
bit like cottage cheese. Cottage cheese is just the curds sieved
from the whey. Other cheeses, like cheddar, are pressed for a long
time to remove more of the liquid. Some cheeses, like smelly
Stilton, have bacteria or fungi added to them whilst they age,
which gives them a different flavour.
To find out more about using bacteria and fungi in cheese, go to
Mighty Microbes.