Food Processing and Technology
Spoilage and the principles of preservation
Stop food from spoiling.
Food goes bad (deteriorates) in three ways: physically, chemically and biologically. We notice bad flavours, a changed texture or colour, and a loss of nutrients.
Causes of spoilage:
- pests and insects;
- the wrong temperature during processing or storage;
- light, oxygen (air) and moisture;
- microbes: bacteria, fungi, moulds;
- chemicals, such as pesticides;
- the food's own enzymes, and changes after harvest or slaughter.
How long foods last:
| Kind | Examples | Keeps for |
|---|---|---|
| Perishable | milk, curd, fish, meat | a day or two |
| Semi-perishable | fruits, vegetables; onions, potatoes | 1-2 weeks; 2-4 weeks |
| Non-perishable | grains, pulses, oilseeds | about a year |
Microbes grow when they have nutrients, moisture, the right pH (acidity) and oxygen. Bacteria like protein-rich foods, called 'high-risk' foods. Enzymes depend on pH and temperature.
So the five principles of preservation are: apply heat; remove moisture; keep food cold; lower the pH (make it more acidic); and control oxygen. For example, a pickle lasts because of its acid, salt and oil. Heat, dry, chill, acidify, keep out air.
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