Why use machines in food making?
Machines do the same job again and again with the same quality. They give speed (more food per hour), evenness (every biscuit alike), cleanliness (fewer hands touch food) and safety for heavy or hot jobs.
Food machines are usually made of stainless steel because it does not rust, is smooth and easy to clean, and does not spoil the taste.
Common manufacturing machines
- Hopper and conveyor belt: hold and carry the material.
- Cleaner and sorter: take away stones, dust and bad pieces.
- Mill or grinder: makes flour or paste (smaller size).
- Cutter and slicer: give pieces of equal size.
- Mixer and kneader: turn blades to mix or make dough.
- Cooker, oven, fryer, dryer: heat the food.
- Filler and sealer: put an exact amount in a pack and close it.
- Sensors: thermometer, weighing scale and metal detector check the product.
Good use: read the manual, wear proper clothing, never reach into a running machine, keep guards in place, use lock-out when cleaning or repairing, clean after each batch (CIP, "clean in place", means cleaning pipes with liquid without opening them) and oil and check parts on a schedule (maintenance).
Boilers and steam
A boiler is a closed steel vessel in which fuel (gas, oil, coal, wood or electricity) heats water into steam. Steam carries a lot of heat: to turn 1 kg of boiling water into steam takes about 2260 kJ (latent heat). When steam touches a cold pot it turns back to water and gives that heat out.
Food factories use steam to cook, sterilise, pasteurise, dry, heat water and clean.
Key safety parts: safety valve (lets steam out if pressure is too high), pressure gauge, water-level gauge (a boiler must never run dry) and a water treatment system. Only trained, licensed persons run boilers and the boiler is inspected by law.
Cooling and refrigeration
Cold slows germs. Equipment includes cold rooms, refrigerators, freezers and blast chillers that cool cooked food very fast.
Most work by the refrigeration cycle: (1) a compressor squeezes a gas, making it hot; (2) the condenser gives that heat to the outside air and the gas becomes liquid; (3) the expansion valve lets the liquid expand and become very cold; (4) the evaporator inside the cold space takes heat from the food and the liquid turns to gas again. The heat is moved out; it is not destroyed.
Cooled food must pass the danger zone (60 °C down to 5 °C) quickly, ideally in a few hours. Keep door openings short and defrost often.
Try it
Fill two cups with hot water. Put one on the table and the other in a bowl of cold water and ice. Check the temperature every 5 minutes with a safe thermometer or by careful touch. The ice bowl cools faster: that is how a chiller works. In the 3D, put the cooler temperature at 0 and watch the colour.
Key formulas and definitions
- Heat needed Q = m × c × ΔT (water: c = 4.2 kJ/kg·°C)
- Heat to make steam from boiling water = m × 2260 kJ/kg
- Time = distance ÷ speed (belt)
- Output per hour = batch size × batches per hour
- Time to cool = Q ÷ power of chiller
Worked examples
1. How much heat is needed to warm 100 kg of water from 20 °C to 90 °C? (c = 4.2 kJ/kg·°C)
Q = 100 × 4.2 × (90 − 20) = 100 × 4.2 × 70 = 29,400 kJ.
2. A belt 12 m long moves at 0.5 m/s. How long does food take to travel along it?
Time = 12 ÷ 0.5 = 24 seconds.
3. A mixer makes 400 kg of dough per batch and runs 5 batches per hour. How much dough in an 8-hour shift?
Per hour: 400 × 5 = 2000 kg. In 8 hours: 2000 × 8 = 16,000 kg.
Common mistakes
- Putting a hand into a running machine "just to check". Always stop and lock the machine first.
- Thinking steam and boiling water at 100 °C carry the same heat. Steam carries much more because of latent heat.
- Thinking a refrigerator makes cold. It moves heat out of the cold space.
- Letting cooked food cool slowly on the counter, so it stays long in the danger zone.