Food Processing Principles and Unit Operations
This domain tests the physical principles behind food processing: mass and energy balances, heat transfer, flow, size reduction, mixing, separation, evaporation and drying. Questions often use simple calculations.
Core concepts
- Unit operations: cleaning, sorting, grading, peeling, size reduction, mixing, filtration, centrifugation, evaporation, drying and heat exchange. Each step has a measurable input and output.
- Mass balance: mass in = mass out + accumulation. Solids balance is especially useful when water is removed.
- Heat transfer: conduction, convection and radiation. Heating rate depends on temperature difference, area, thickness and thermal conductivity.
- Drying and evaporation: remove water to lower water activity. Wet-basis and dry-basis moisture must not be mixed.
Worked example
100 kg of tomatoes contain 5% total solids, so solids = 5 kg. The tomatoes are concentrated to a paste with 25% total solids. If no solids are lost, final paste mass = 5 ÷ 0.25 = 20 kg. Water removed = 100 − 20 = 80 kg. The calculation uses a solids balance because solids are conserved while water is removed.
Traps
Using the wrong moisture basis; ignoring losses during peeling or filtration; assuming all input becomes product; mixing up evaporation and drying; forgetting that heat transfer slows as product thickness increases.