Primary and secondary processing
- Primary processing turns raw food into a form that can be eaten or used: cleaning, sorting and grading vegetables, milling wheat into flour, and pasteurising milk.
- Secondary processing turns primary processed foods into other products: flour into bread, pasta or cakes; milk into cheese or yoghurt.
Preserving food
- Pasteurisation heats milk to about 72°C for 15 seconds, then cools it quickly. It kills most harmful bacteria, with little change in taste.
- UHT (ultra heat treatment) heats milk to about 135°C for 1 to 2 seconds; it keeps unopened for months but tastes slightly different.
- Sterilisation and canning heat food in a sealed container to kill all micro-organisms.
- Chilling, freezing, drying, and modified atmosphere packaging (MAP, changing the gases in the pack) all slow spoilage.
- Heat processing can destroy some water-soluble vitamins, such as vitamin C and B1.
Changing nutritional value
- Fortification adds nutrients to foods: UK law requires white flour to have calcium, iron, thiamin (B1) and niacin (B3) added, and many breakfast cereals are fortified with vitamins and iron.
- Some foods are modified to be lower in fat, sugar or salt.
- Processing can add salt, sugar and fat, so highly processed foods should be eaten in moderation.
Key terms
- Primary processing
- Changing raw food into a form that can be eaten or used.
- Secondary processing
- Turning primary processed foods into other products.
- Pasteurisation
- Heating to about 72°C for 15 seconds to kill harmful bacteria.
- UHT
- Ultra heat treatment: heating to about 135°C for 1 to 2 seconds.
- Fortification
- Adding nutrients to a food.
- Modified atmosphere packaging
- Changing the gases in a pack to slow spoilage.
- Sterilisation
- Heating to kill all micro-organisms.