Food manufacturing equipment: the big picture
A small kitchen cooks for a family. A factory makes thousands of packs a day, so it uses machines. They fall into a few groups:
- Moving and washing: belts, pumps, washers.
- Cutting and shaping: cutters, fillet machines, mixers, moulds.
- Heating: cookers, ovens, dryers, sterilisers (retorts). They need heat, usually from steam made by a boiler.
- Cooling: chillers, freezers, cold stores. They need a refrigeration machine.
- Packing and checking: filling, sealing, metal detectors, weighing.
Good machines are made of stainless steel, because it does not rust and is easy to wash. A machine must be easy to clean, safe for workers, and must not drop anything into the food.
Boilers: making steam
A boiler is a closed steel tank. Fuel (gas, oil, coal or wood waste) burns in a furnace under or inside it. The heat boils the water and makes steam. Steam carries a lot of heat, and when it touches something cool it turns back into water and gives that heat away. That is why steam cooks, dries and sterilises so well.
Where steam is used: cooking fish and crab, heating retort cans, cleaning machines, warming water for washing.
Safety parts of every boiler:
- Pressure gauge shows how strong the steam is.
- Safety valve opens by itself and lets steam out if pressure gets too high.
- Water-level gauge shows the water height. If the tank runs dry, it can overheat and break.
- Feed-water pump adds fresh water.
Boilers must be checked by trained people on a fixed schedule, and only licensed operators run big ones. Hard water leaves a white crust (scale), so the water is treated.
Freezing and refrigeration equipment
Cold does not come from nowhere. A refrigeration machine moves heat from inside the cold room to the outside air. A special gas (the refrigerant, for example ammonia in big plants) goes round a closed loop with four parts:
- Evaporator: inside the freezer. The cold liquid boils into gas and takes heat from the fish and air.
- Compressor: squeezes the gas. It becomes hot and under pressure. It is the motor of the loop.
- Condenser: outside. The hot gas gives its heat to air or water and turns into liquid.
- Expansion valve: a narrow opening. Pressure drops suddenly and the liquid becomes very cold. Then it enters the evaporator again.
Types of freezers for fish:
- Air-blast freezer: very cold air is blown over the fish.
- Contact (plate) freezer: fish blocks are pressed between cold metal plates. Fast for flat blocks.
- Brine or immersion freezer: fish goes into very cold salty water. Used on fishing boats.
- IQF (individually quick frozen): each prawn or fillet freezes separately, so they do not stick together.
Frozen fish is kept in a cold store at -18 °C or colder (fatty tuna for raw eating is often kept much colder, around -50 °C). The temperature must stay steady: warm-and-cold swings make big ice crystals that spoil the texture. Ammonia leaks are dangerous, so plants have gas alarms.
Try it yourself
In the 3D: first guess, then check. Move the heat slider to 0. Will steam flow? (No.) Now push it to 100. Does the fish cook faster? Next set the freezer to -30. Is the fish colder than at -18?
At home: put your hand behind a running fridge (do not touch the pipes if very hot). The warm air is the heat that came out of your food box. Also watch a pressure cooker: steam comes out of the vent when water boils inside. Ask an adult to help.
Key formulas and definitions
- Boiler: fuel heat → water → steam → used for cooking, sterilising, cleaning
- Refrigeration loop: evaporator → compressor → condenser → expansion valve → evaporator
- Heat is moved OUT of the cold room, so the condenser side is warm
- Safe frozen storage: -18 °C or colder
- Temperature fall = starting temperature − final temperature
- Time = amount of fish ÷ freezing rate
Worked examples
1. Fish enters a freezer at 8 °C and must reach -18 °C. By how many degrees must it cool?
Fall = 8 − (−18) = 8 + 18 = 26 °C.
2. A plate freezer freezes 150 kg of fish blocks every hour. How long to freeze 600 kg?
Time = 600 ÷ 150 = 4 hours.
3. A boiler makes 250 kg of steam per hour. A cooker uses 40 kg of steam per batch. How many batches can it run in one hour?
Batches = 250 ÷ 40 = 6.25, so 6 full batches (the leftover steam is not enough for a seventh).
4. In the refrigeration loop, where does the gas pick up heat and where does it give heat away?
It picks up heat in the evaporator (inside the freezer) and gives heat away in the condenser (outside).
Common mistakes
- Thinking a freezer "makes cold". It only moves heat from inside to outside.
- Forgetting the safety valve and water-level gauge. A boiler without them can burst.
- Mixing up the evaporator (cold, inside) and the condenser (warm, outside).
- Storing frozen fish at -5 °C. Safe storage is -18 °C or colder.