Food science, processing and technology
Food science studies what food is made of and how it changes. Food processing turns raw crops and animal products into food that is safer, tastier or longer-lasting: washing, cutting, cooking, drying, milling, packing. Food technology uses science and machines to do this on a large scale, and food manufacturing is the factory production of ready foods such as bread, biscuits, juices and noodles.
Levels of processing
- Minimally processed: cleaned, cut or chilled, still close to fresh (washed salad, frozen peas, pasteurised milk).
- Moderately processed: changed form (flour, cheese, jam, canned beans).
- Highly processed: many steps and added ingredients (chips, instant noodles, soft drinks).
Why food spoils and why we preserve it
Food spoils for five main reasons:
- Microbes: bacteria, moulds and yeasts grow fast in warm, moist food. Some only spoil taste; others cause food poisoning.
- Enzymes: the food's own enzymes keep working after harvest (a cut apple turns brown, bananas over-ripen).
- Air: oxygen makes fats go rancid.
- Moisture and temperature speed up all of these.
- Pests and damage: insects, rats and bruising.
Why preserve?
- Keep food safe to eat.
- Reduce waste: a large share of fruit and vegetables is lost after harvest in many countries.
- Have seasonal food all year and move food long distances.
- Earn more by selling later or as products.
Methods of food preservation
| Method | What it removes or does | Examples |
|---|---|---|
| Drying / dehydration | Removes water | Raisins, dried fish, milk powder, papad |
| Salt or sugar | Pulls water from microbes (osmosis) | Salted fish, jam, murabba, jelly |
| Refrigeration (0–5 °C) | Slows microbes and enzymes | Milk, vegetables |
| Freezing (−18 °C) | Almost stops growth; turns water to ice | Frozen peas, meat, ice cream |
| Pasteurisation | Mild heat kills most harmful microbes (about 72 °C for 15 s) | Milk, juice |
| Boiling, sterilisation, canning | Strong heat in a sealed container | Canned beans, UHT milk |
| Acid (pickling) and fermentation | Low pH stops most microbes | Pickles, curd, sauerkraut, kimchi |
| Smoking | Dries and adds antimicrobial smoke | Smoked fish and meat |
| Permitted preservatives | Chemicals in safe amounts (sodium benzoate, potassium metabisulphite) | Squash, sauces |
| Vacuum / modified-atmosphere packing | Removes oxygen | Packed cheese, coffee |
| Irradiation | Controlled radiation kills microbes and stops sprouting | Spices, onions in some countries |
Classifying foods by perishability
- Perishable: spoil in a few days unless chilled: milk, meat, fish, eggs, soft fruits, leafy greens.
- Semi-perishable: last weeks to a few months if kept cool and dry: potatoes, onions, apples, nuts, flour.
- Non-perishable (stable): last many months when stored dry: grains, pulses, sugar, salt, dried spices, canned food.
The more water a food has, the faster it usually spoils.
Post-harvest storage and value addition
Storage
After harvest, crops must be cleaned, graded, dried to safe moisture (for grain about 12–14%) and stored. Good stores keep out water, pests and rats.
- Grain: traditional bins, metal silos, hermetic bags, warehouses with fumigation.
- Fruits and vegetables: cool chambers, cold storage and controlled-atmosphere stores; a cold chain keeps food cold from farm to shop.
Value addition
Value addition means changing a raw product so it sells for more: grading and packing, or processing it into a new product.
- Tomato → puree, ketchup, sauce.
- Milk → curd, paneer, cheese, ghee.
- Wheat → flour → bread and biscuits.
- Mango → pulp, juice, pickle, dried slices.
It creates jobs, cuts waste and raises farm income.
Try it: the bread test
Keep three bread slices: one sealed on the shelf, one in the fridge, one sun-dried. Note the day mould appears on each. The shelf slice usually goes first (warm and moist), the fridge slice later (cold), and the dry slice may not mould at all (no water). You have tested two letters of WATT.
Key formulas and definitions
- Microbes need water + warmth + food + time; remove one to preserve food
- Danger zone for bacteria: about 5 °C to 60 °C
- Pasteurisation (HTST): about 72 °C for 15 seconds, then quick cooling
- Freezing: −18 °C or colder; refrigeration: 0–5 °C
- Pickling: pH below about 4.5 stops most harmful bacteria
- Value added = selling price of product − cost of raw material and processing
Worked examples
1. Why does jam not spoil easily even at room temperature?
Jam has a very high sugar content. Sugar draws water out of microbe cells by osmosis, so they cannot grow. The jar is also sealed and heated when filled.
2. Classify: rice, fish, onion, milk, sugar, apple.
Perishable: fish, milk. Semi-perishable: onion, apple. Non-perishable: rice, sugar.
3. A farmer sells 100 kg of tomatoes at ₹20/kg. Processing them gives 40 kg of ketchup sold at ₹150/kg, with ₹2,500 processing cost. Find the value added.
Raw sale = 100 × 20 = ₹2,000. Ketchup sale = 40 × 150 = ₹6,000. Value added = 6,000 − 2,000 − 2,500 = ₹1,500 extra over selling raw.
Common mistakes
- Thinking a fridge kills microbes. It only slows them; food still spoils, just more slowly.
- Thinking pasteurised milk is sterile. Pasteurisation kills most harmful microbes, but the milk still needs refrigeration.
- Refreezing thawed food many times. Microbes grow during each thaw.
- Thinking all preservatives are harmful. Permitted preservatives in legal limits are safe; salt, sugar and vinegar are preservatives too.