Transcript Dairy products

Culinary Science
Second years
Lesson 3 – dairy
How do you make cheese?
Proteins in milk
Group 1 - the caseins.
The caseins exist as big bundles – about a thousand of proteins
(micelles), glued together by the calcium ions.
Kappa-casein caps micelles when a certain size → stops them
getting bigger, and keeps them separate (is negatively charged,
so they repel)
Very stable to heating
Calcium
-
Capping casein
Casein
Group 2 - the whey proteins
proteins
Much less common (Curds:whey (4:1) ).
Important in milk foams – lactoglobbulin unwinds and surrounds
air bubbles
In the presence of acid
Milk normally pH 6.5.
At pH 5.5, capping caseins negative charge is neutralised, and the
micelles can no longer repel, and fall apart
At pH 4.7, they start to bond to each other to form a continuous
network – the milk solidifes/curdles
Add lemon juice/vinegar to milk → small white particles will appear
(the casein proteins coagulate).
Then heat - lactoglobulin proteins will also coagulate - the white
particles become bigger and more visible as they stick together.
Making yoghurt and cheese
When bacteria contaminate milk, bacteria degrade lactose →
lactic acid.
↑ acidity causes the casein proteins to denature + coagulate.
The coagulated casein network can trap within it the water and
the fatty material
Lactococcus lactis, Streptococcus salvarius, Lactobacillus
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Soft cheeses - fairly high water content (50-75%), unpressed,
short shelf life eg mascarpone, cottage cheese, cream cheese
etc
Hard cheeses - lower water content. Subjected to large pressure
to squeeze out the water – longer shelf life!
Cheese manufacture
WHEY will not keep - should be
drunken directly
This acid milk gel, when broken or cut, forms:
CURDS can be stored for
future use. Shelf-life can be
further increased by salting
or drying
Soon discovered that enzymes (eg the protease from the stomach of
a milk-fed calf – rennet) can also cause casein to coagulate.
It gives the micelles a haircut – it clips off the capping casein – the
micelles clump together without the milk becoming sour
Final stages of cheese making:
• Salting
• Maturing/ripening stage – a complex set of biochemical
changes that provides flavour
• May take up to two years
Make some dairy products!
• Make yoghurt
• Make paneer –
vary the fat
content
• Make mascarpone
Paneer
http://www.bbc.co.uk/food/recipes/paneer_86451
Ingredients
2 litres whole milk, 2 tbsp lemon juice
Preparation method
• Bring the milk to the boil in a heavy-based saucepan.
• Once the milk starts to boil and rise up, stir in the lemon juice.
Keeping the milk on the heat, stir gently to help the milk curdle;
it should only take about a minute. The curds will coagulate and
separate from the watery whey.
• Remove from the heat.
• Line a large sieve with muslin or cheesecloth and place over a
large bowl or saucepan. Strain the cheese into the sieve and run
some cold water through it. Discard the whey or use for another
purpose.
Mascarpone
Recipe from cheese course - Cutting the Curd
• Heat the cream to 80C – don't let it catch
• Add tartaric acid (1/4 teaspoons for 1 litre
double cream) and stir – the mixture should
thicken and flecks will form
• Strain in cheesecloth
Try and make cheese
Rennet v bacteria v both
• 1 litre whole milk
• Warm milk to 38 C
• Remove from the heat and add the culture (or
rennet if no culture) as per guidelines (4
teaspoons liquid rennet diluted in 4 teaspoons
cool, unchlorinated water)
• If adding rennet, wait for 45 minutes before
adding rennet
• Leave some at 37 C overnight
Bibliography
• McGee on Food and Cooking. By Harold McGee
• The Science of Cooking. By Peter Barham
• Food Preservation: an introduction, Tim Hutton
• Molecular Gastronomy manual from www.inicon.net
• Recipe ideas from Herve This
• Images/pictures – from Internet