Discuss the causes of food spoilage and the factors that affect it.

1. 1 · Open in two lines. Food spoilage is any change that makes food unfit or undesirable to eat. It wastes food, lowers nutritive value and can make people ill.
2. 2 · Microorganisms.
   • Bacteria, yeasts and moulds break down protein, carbohydrate and fat.
   • They cause souring, gas, slime, off-odours and sometimes toxins: sour curd, mouldy bread, slimy rice.
3. 3 · Enzymes, pests and chemical reactions.
   • The food's own enzymes: browning of cut brinjal, over-ripening of banana.
   • Insects and rodents: weevils in dal, rats in godowns.
   • Non-enzymic changes: rancidity of oil, Maillard browning.
4. 4 · Physical factors. Heat, cold, moisture, dryness, light, air, time and bruising.
5. 5 · Draw a table of factors. [Table: intrinsic (aw, pH, nutrients, redox potential, natural antimicrobials, covers) vs extrinsic (temperature, humidity, gases)]
6. 6 · Give the water activity limits. Most spoilage bacteria need aw 0.91, yeasts 0.88, moulds 0.80; so moist foods spoil by bacteria, and bread and jams by moulds and yeasts.
7. 7 · Nutrition link. In a hospital kitchen, control these causes with clean handling, the 5-60 °C danger-zone rule, pest-proof stores and FIFO.
8. 8 · Close in one line. Every preservation method works by removing or controlling one or more of these causes.

Scoring tip: Group the causes under five heads with one Indian kitchen example each; the water activity numbers earn the extra marks.