Transcript Dairy food and cheese making File

Dairy food and cheese-making
Dairy
• Dairy products are foods that are made from
milk
• Examples: cream, milk, cheese, yoghurt
• The molecules in milk includes ALL those
required for a growing baby mammal. It is the
only food source mammal have until they are
weaned off their mother’s milk.
How does milk make cheese?
• Milk needs to be coagulated, the solids (curds)
are then separated from the liquids (whey)
• Coagulation is the process of the proteins in
milk (casein) becoming tangled into solid
masses, called curds.
• In cow’s milk approximately 80% of the
protein is casein
How does milk coagulate?
• Milk curdles (coagulates) when the pH
becomes acidic or an enzyme is added (eg.
rennin)
• Milk will coagulate by adding:
– An edible acid like lemon juice or vinegar
– Lactic acid bacteria or yeast
– rennet (from the stomach of mammals that
contains the enzyme rennin)
pH
• What is pH (definition)?
• Complete the following table:
Acidic
Acidic
substances foods
Neutral
Neutral
substances foods
Basic
Basic
substances foods
Acids added to milk
• By adding an acid to milk it changes the acidity
of the liquid (the pH).
• When the pH gets below about 5, the proteins
denature (change shape) and chemically
change to form larger molecules that are
hydrophobic proteins (solid, masses called
curds)
Lactic acid bacteria
• These are organisms that use the sugar,
lactose, in anaerobic respiration
• The bacteria produce lactic acid which lowers
the pH of the milk, that results in coagulation
• The bacteria used are low-pH tolerant species
and so can survive where other pathogenic
species cannot
Rennet contains an enzyme, rennin
• Enzymes are special proteins
• They are present in the cytoplasm of all cells
• They help to speed up the chemical reactions
in the cell
• There are hundreds of different enzymes but
each enzyme speeds up only one kind of
reaction
• Rennin makes casein hydrophobic, causing it
to form solids in the whey
Yeast
• Yeast is a type of fungus, or mold.
• These are organisms that also use sugars in
anaerobic respiration but the chemical
reaction is different because their anaerobic
respiration makes ethanol and carbon dioxide
(not lactic acid).
• Yeast and other types of fungi are used to add
flavor to cheese, such as blue cheese and
camembert.