Food Processing Operations and Equipment (cleaning, grading, milling, size reduction, mixing, separation)
What the exam tests
This domain tests unit operations and equipment selection: cleaning, grading, milling, size reduction, mixing and separation. You should be able to name the principle behind a machine and calculate simple separation or loss efficiencies.
Core rules and concepts
- Cleaning removes foreign matter by screening, aspiration, magnetic separation, destoning and washing; grading sorts by size, shape, density or quality.
- Milling reduces particle size. Roller milling is gradual and selective for wheat; hammer mills use impact; plate mills use shear. Separation uses screens, air classification, centrifugation, filtration and expression.
- Mixing needs sufficient time, but over-mixing can cause segregation or damage. Homogenisation reduces droplet size and stabilises emulsions.
- Product-contact surfaces should be stainless steel, smooth, cleanable and free of crevices.
- Equipment capacity depends on feed rate, residence time and the desired degree of separation, not on motor size alone.
Worked example
A destoner receives 1,000 kg of grain containing 100 kg stones. It removes 95 kg of stones but also carries away 10 kg of grain. Stone removal efficiency = 95 divided by 100 = 95%. Grain loss = 10 divided by 900 = 1.11% of the grain feed. The two figures use different bases: stone recovery is based on stones in the feed, while grain loss is based on grain in the feed. Reporting a single 95% figure hides the grain loss.
Traps
Using grading and sorting as synonyms; calculating both efficiencies on the total feed; ignoring grain loss in a destoner; confusing milling with grinding only; failing to clean equipment between products.