Food Processing Unit Operations
5. Food Processing Unit Operations
This domain tests the individual physical operations used across food plants and the material and energy balances behind them. Expect questions on equipment choice, operation sequence and simple mass balances.
Core rules
- Preparatory operations: cleaning, sorting, grading, peeling, size reduction and mixing.
- Separation operations: filtration, centrifugation, pressing, membrane processing and extraction.
- Thermal operations: blanching, pasteurisation, evaporation, drying, baking, frying and extrusion.
- Conservation operations: chilling, freezing, drying, concentration, irradiation and packaging.
- Solids balance is the key calculation: solids before = solids after, unless material is added or removed.
- Equipment examples: plate heat exchanger for milk, pulper for fruit, spray dryer for milk powder, drum dryer for flakes, reverse osmosis for concentration.
Worked example
Concentrate 1,000 kg fruit juice from 10% to 40% solids in an evaporator. Solids in feed = 1,000 × 0.10 = 100 kg. Final mass = 100 / 0.40 = 250 kg. Water removed = 1,000 − 250 = 750 kg. Reasoning: solids are conserved during evaporation, so divide the solids by the final solids fraction; the difference is evaporated water.
Traps
Do not assume final mass equals initial mass minus only water lost without using the solids balance. Do not confuse evaporation with drying. Reverse osmosis is not a thermal process. Centrifugation separates by density, not by size alone.