Milk, Meat, Poultry and Fish Processing
Milk
Milk is about 87% water; cow milk typically has 3.5% fat and 8.5% solids-not-fat. Reception tests include organoleptic, acidity, alcohol and clot-on-boiling. Flow: chill to 4 °C → test → filter → separate cream by centrifuge → standardise fat → homogenise at 200–250 bar → pasteurise (72 °C for 15 s HTST, or 135–150 °C for 2–4 s UHT) → cool and fill. Products include butter, ghee, paneer, curd, flavoured milk and skim milk powder. Paneer is made by acid coagulation at about 80 °C followed by pressing.
Meat, poultry and fish
After slaughter, muscle passes through rigor mortis and pH falls from about 7 to 5.5. Conditioning or ageing improves tenderness; freezing before rigor resolves causes thaw rigor and tough, drip-lossy meat. Curing uses salt, sugar and nitrite within limits, often with smoking. Fish spoil fastest: chill immediately, hold at 0–2 °C on ice, and use TVB-N or histamine as spoilage indicators; scombroid fish can form histamine if poorly handled.
Worked example
1000 kg milk at 4.5% fat is to be standardised to 3.5% using skim milk at 0.05% fat. Skim milk needed = 1000 × (4.5 − 3.5)/(3.5 − 0.05) = 1000 × 1.0/3.45 ≈ 290 kg. Adding 290 kg skim milk gives about 1290 kg at 3.5% fat. Reasoning: fat is conserved, so the balance equation and the Pearson square give the same answer.
Traps
Calling UHT pasteurisation; adding cream when the aim is to reduce fat; exceeding the permitted nitrite level; refreezing thawed meat; storing fish with ready-to-eat foods; forgetting that butter and ghee have different moisture limits.