Milk and Milk Product Processing
Milk processing converts a highly perishable secretion into safe fluid milk and products such as cream, butter, curd, cheese and powder. The exam tests composition, pasteurization, homogenization, cream separation, standardization, fermented products and adulteration tests.
Core rules
- Milk contains water, fat, protein, lactose and minerals. Fat is dispersed as globules; cream separation uses centrifugation.
- Pasteurization uses a validated time-temperature combination, such as 72 °C for 15 s (HTST), followed by rapid cooling. It reduces pathogens but does not sterilize.
- Homogenization reduces fat globule size and prevents cream separation.
- Standardization adjusts fat content by mixing whole milk with skim milk or cream.
- The phosphatase test indicates inadequate pasteurization; alkaline phosphatase is inactivated by correct heating.
- Fermented products depend on controlled cultures, hygiene and incubation temperature.
Worked example
1000 kg milk at 3.5% fat is standardized to 3.0% fat using skim milk at 0.1% fat. Let skim = x and whole milk = 1000 − x. Fat balance: 0.1x + 3.5(1000 − x) = 3000. Solving gives x = 147.1 kg skim milk and 852.9 kg whole milk. The reasoning conserves fat mass.
Traps
- Calling pasteurization sterilization.
- Assuming homogenization kills microorganisms.
- Using the wrong fat basis in standardization.
- Ignoring cleaning of separators and pasteurizers.
- Relying on smell alone to detect adulteration.