Food spoilage and its causes
Milk left outside on a hot day turns sour by evening. A banana turns black after some days. Bread kept in a damp box gets green fuzz. These are all signs that food is spoiling.
Food spoilage (अन्न नासणे) is a change in the colour, odour, texture, quality or taste of food, with loss of nutrients. Spoiled food can make us ill.
In the figure : In the figure the causes of spoilage are shown: A micro-organisms from the air, water or soil, B insects, C a chemical reaction of the food with a metal, D factors within the food (a fruit turning black).
Rule 1: Causes of spoilage — (1) Factors within the food: fruits turn black, meat turns sour, peanuts become rancid. (2) Wrong handling, storage and transport. (3) Chemical reaction of acidic or alkaline food (meat, milk) with metals. (4) Contamination by micro-organisms or insects from air, water or soil.
- Easy : Cut apple turns brown by itself: factor within the food.
- Medium : Curd kept in a copper vessel may react with it: reaction with a metal.
- Exam-type : Wheat flour in an open bin gets insects and moulds: contamination.
Four causes: inside the food, wrong handling, reaction with metal, contamination.
Thinking spoiled food is spoiled only if it smells bad. Colour, texture, taste also change, and some spoiled food looks fine.
Memory clue: Spoilage = Smell, Colour, Taste, Texture change (S-C-T-T).
Spot the difference
| Cause | Example |
|---|---|
| Factors within food | Fruit turning black |
| Metal reaction | Milk or meat in a metal vessel |
| Contamination | Microbes, insects from air, water, soil |
Practice questions
- 1What is food spoilage?
- 2Name two signs of spoiled food.
- 3Which foods can react with metals?
- 4Give an example of a factor within the food that spoils it.
- 5What happens to peanuts when they spoil?
- 6Name two kinds of contaminants in food.
- 7In the figure, name the cause of spoilage shown by A, B and C.
- 8Rohan says only bad smell means spoiled food. Correct him.
Show answers (try them yourself first)
- 1A change in colour, odour, texture, quality or taste with loss of nutrients.
- 2Bad odour and change in colour.
- 3Acidic or alkaline foods like meat and milk.
- 4Fruits turn black.
- 5They become rancid.
- 6Micro-organisms and insects.
- 7A: micro-organisms, B: insects, C: reaction with a metal.
- 8Colour, texture and taste also change; some spoiled food can look fine.
Food wastage and its prevention
At a wedding feast, plates are heaped with food and half of it ends in the dustbin. In the field some grain falls and is lost while harvesting. Food is lost at many steps before it reaches us.
Quantitative wastage (प्रमाणात्मक नासाडी) means food is lost in amount. Qualitative wastage (गुणात्मक नासाडी) means food loses quality or nutrients.
In the figure : In the figure P is grain spilled by wrong handling (quantitative wastage). Q is over-cooked food (qualitative wastage). R is too much food served (quantitative wastage).
Rule 1: Quantitative wastage — Causes: wrong farming methods (hand sowing, inadequate threshing), improper storage and distribution, and serving too much food at feasts.
- Easy : Serving too much food that is left on the plate.
- Medium : Grain spilled during transport.
- Exam-type : Inadequate threshing leaves grain in the husk.
Rule 2: Qualitative wastage and prevention — Causes: wrong protection methods, excess preservatives, over-cooking, washing vegetables after cutting, mishandling fruits and wrong estimate of transport time. To prevent: serve only what you can eat, avoid over-cooking, re-use left-overs, buy only what you need, store properly and check expiry dates.
- Easy : Over-cooking destroys nutrients: qualitative wastage.
- Medium : Washing vegetables after cutting washes away nutrients.
- Exam-type : World Food Day is on 16 October; it reminds us not to waste food.
Quantity lost = quantitative; quality lost = qualitative. Take only what you can eat.
Thinking leftover food is always waste. Safe left-overs can be re-used.
Memory clue: Quantity = Quantity of food lost; Quality = Quality (nutrition) lost.
Spot the difference
| Type | Meaning | Example |
|---|---|---|
| Quantitative | Amount of food lost | Spilled grain, too much served |
| Qualitative | Quality or nutrients lost | Over-cooking, washing after cutting |
| Prevention | Plan and store well | Check expiry dates |
Practice questions
- 1What is quantitative wastage?
- 2What is qualitative wastage?
- 3Give one cause of quantitative wastage.
- 4Give one cause of qualitative wastage.
- 5When is World Food Day?
- 6Name two ways to prevent food wastage.
- 7Classify as quantitative or qualitative: (a) spilled grain, (b) over-cooked vegetables, (c) too much food served.
- 8Your school plans a lunch for 100 children. Suggest two ways to avoid wastage.
Show answers (try them yourself first)
- 1Loss of food in amount.
- 2Loss of quality or nutrients of food.
- 3Serving too much food at feasts.
- 4Over-cooking.
- 516 October
- 6Serve only what you can eat; check expiry dates.
- 7(a) quantitative, (b) qualitative, (c) quantitative.
- 8Cook only as much as needed and let children take small portions; store left-overs properly.
Food protection and preservation
Grandmother makes pickle with lots of salt and oil so that it lasts all year. A refrigerator keeps milk fresh for days. A packet of wafers is puffed up with gas inside. All these are ways to keep food safe.
Food protection (अन्न संरक्षण) is preventing spoilage by microbial growth and pests. Food preservation (अन्न परिरक्षण) uses preservatives to prevent spoilage due to internal factors for a long time.
In the figure : In the figure protecting food: A a refrigerator (low temperature slows reactions), B an inert gas (nitrogen) in a packet, C insecticide sprayed on gunny bags, D natural preservatives (salt, oil) in a pickle.
Rule 1: Methods — Freezing: reactions slow at low temperature. Insecticides on gunny bags. Inert gas: nitrogen in wafer packets. Natural preservatives: salt, sugar, oil. Chemical preservatives: vinegar (acetic acid), citric acid, sodium benzoate, nitrates and nitrites.
- Easy : Freezing: low temperature slows reactions.
- Medium : Salt, sugar and oil are natural preservatives (pickle, jam).
- Exam-type : Nitrogen in a wafer packet is inert, so it does not spoil the wafers and keeps oxygen out.
Protect: against microbes and pests. Preserve: use preservatives for long storage.
Using chemical preservatives in large amounts. Excess preservatives can harm; use only the permitted amount.
Memory clue: Natural: Salt, Sugar, Oil (SSO); Chemical: Vinegar, Citric acid, Benzoate.
Spot the difference
| Method | How it works | Example |
|---|---|---|
| Freezing | Slows reactions | Refrigerator |
| Natural preservative | Prevents microbial growth | Salt, sugar, oil |
| Inert gas | Keeps oxygen out | Nitrogen in wafers |
Practice questions
- 1What is food protection?
- 2What is food preservation?
- 3Name two natural preservatives.
- 4Name two chemical preservatives.
- 5Which gas is used in wafer packets?
- 6Why does freezing preserve food?
- 7How are food grains in gunny bags protected?
- 8A shopkeeper puts too much preservative in jam to make it last longer. Is it right? Explain.
Show answers (try them yourself first)
- 1Preventing spoilage by microbial growth and pests.
- 2Using preservatives to prevent spoilage for a long time.
- 3Salt and sugar (or oil).
- 4Vinegar (acetic acid) and sodium benzoate.
- 5Nitrogen
- 6Chemical reactions slow down at low temperature.
- 7By spraying insecticides on the bags.
- 8No. Excess preservatives can be harmful; only permitted amounts should be used.
Pasteurisation, irradiation and institutions
Packet milk in a shop stays good for days without a refrigerator because it has been heated and sealed. Onions and spices are treated with a special ray so that they last longer. A government body also checks food quality.
Pasteurisation (पाश्चरीकरण) is heating milk and cooling it quickly to destroy microbes. Irradiation (किरणोत्सर्ग प्रक्रिया) is exposing food to rays to kill microbes and insects.
In the figure : In the figure of pasteurisation (a sketch) the milk is heated to 80 °C, kept at 80 °C for 15 minutes and then cooled quickly.
Rule 1: Pasteurisation — Milk is heated, for example at 80 °C for 15 minutes, then cooled quickly. This destroys microbes. It was developed by Louis Pasteur.
- Easy : Heat milk to 80 °C.
- Medium : Keep it there for 15 minutes, then cool quickly.
- Exam-type : Heating 4 batches of 15 minutes each takes 4 × 15 = 60 minutes in total.
In the figure : In the figure irradiation delays sprouting: after 30 days the irradiated potatoes (P) have not sprouted but the others (Q) have.
Rule 2: Irradiation and FSSAI — Food is exposed to X-rays, gamma rays or high-energy electrons. This kills microbes and insects and delays ripening and sprouting. Plants: Lasalgaon (onions, potatoes) and Navi Mumbai (spices). FSSAI was set up under the Food Safety and Standardization Act, 2006.
- Easy : Irradiation delays sprouting of potatoes.
- Medium : Lasalgaon irradiates onions and potatoes; Navi Mumbai irradiates spices.
- Exam-type : FSSAI was set up in 2006, so it is a legal body that looks after food safety standards.
Pasteurise: 80 °C, 15 min, cool quickly. Irradiation: X-rays/gamma rays. FSSAI: 2006.
Thinking pasteurisation is boiling the milk fully. It is heating for a fixed time and then cooling quickly.
Memory clue: Pasteur → Pasteurisation (milk); Irradiation → Rays.
Spot the difference
| Process | Used on | How |
|---|---|---|
| Pasteurisation | Milk | 80 °C for 15 min, cool quickly |
| Irradiation | Onions, potatoes, spices | X-rays, gamma rays |
| FSSAI | Food safety standards | Set up in 2006 |
Practice questions
- 1What is pasteurisation?
- 2Who developed pasteurisation?
- 3State the temperature and time for pasteurisation given in the lesson.
- 4What is irradiation?
- 5Name two benefits of irradiation.
- 6Where are the irradiation plants for onions and spices?
- 7Under which law was FSSAI set up, and when?
- 8After 30 days, irradiated potatoes have not sprouted but others have. Explain.
Show answers (try them yourself first)
- 1Heating milk and cooling it quickly to destroy microbes.
- 2Louis Pasteur
- 380 °C for 15 minutes.
- 4Exposing food to X-rays, gamma rays or high-energy electrons.
- 5Kills microbes and insects; delays sprouting and ripening.
- 6Lasalgaon (onions, potatoes) and Navi Mumbai (spices).
- 7Food Safety and Standardization Act, 2006.
- 8Irradiation delays sprouting.
Food adulteration and its detection
Turmeric that looks too bright, rava that clings to a magnet, and milk that is thin — these may be cheats. Some sellers add cheap or harmful things to food to earn more. We can catch many with simple tests at home.
Adulteration (भेसळ) is removing important components of food, mixing low-quality or harmful material, or adding harmful substances.
In the figure : In the figure water in milk: a drop of pure milk on an inclined slide leaves a milky-white trail (P); milk with water added does not (Q).
Rule 1: Adulteration and harm — Examples: removing fat from milk; adding small stones, sand, iron filings, urea or sawdust. It can cause poisoning, organ damage and cancer.
- Easy : Water added to milk lowers its quality.
- Medium : Sand mixed in grain can hurt teeth.
- Exam-type : Harmful adulterants like urea can damage organs.
Rule 2: Test 1: milk and chilly powder — Milk + water: a drop on an inclined slide leaves a milky trail if pure; not if water is added. Chilly powder + brick dust: in water the red layer settles at the bottom in the adulterated sample.
- Easy : Milk test: milky trail → pure.
- Medium : Chilly test: red layer at the bottom → brick dust.
- Exam-type : Put powder in water; heavier brick dust sinks first.
In the figure : In the figure of brick dust in chilly powder, put the powder in water. In Q a red layer settles at the bottom, so it is adulterated.
In the figure : In the figure of metanyl yellow in turmeric, after HCl is added the pure turmeric (P) stays yellow, but the red colour stays in the adulterated turmeric (Q).
Rule 3: Test 2: turmeric and rava — Turmeric + metanyl yellow: with HCl the red colour stays in adulterated turmeric. Rava + iron filings: a magnet pulls out the iron filings.
- Easy : Pure turmeric stays yellow with HCl.
- Medium : Red colour stays with metanyl yellow.
- Exam-type : A magnet passed over rava picks up iron filings.
In the figure : In the figure of iron filings in rava, a magnet (A) attracts the iron filings (B) out of the rava (C).
Rule 4: Laws — The Prevention of Food Adulteration Act was passed in 1954. The 1976 amendment provides life imprisonment for harmful adulteration. The Food Safety and Standardization Act came in 2006.
- Easy : Act of 1954 → amendment in 1976: 1976 − 1954 = 22 years later.
- Medium : From the 1976 amendment to the 2006 Act: 2006 − 1976 = 30 years.
- Exam-type : From 1954 to 2006: 2006 − 1954 = 52 years of changing laws.
In the figure : In the figure A is the Prevention of Food Adulteration Act (1954). B is the 1976 amendment, which provides life imprisonment for harmful adulteration. C is the Food Safety and Standardization Act (2006).
Four home tests: milk-slide, chilly in water, turmeric with HCl, rava with magnet.
Tasting suspicious food to check it. Never taste a suspected adulterant; use the test.
Memory clue: Milk – Slide; Chilly – Sink; Turmeric – HCl; Rava – Magnet.
Spot the difference
| Food | Adulterant | Test |
|---|---|---|
| Milk | Water | Drop on inclined slide |
| Chilly powder | Brick dust | Put in water; red layer settles |
| Rava | Iron filings | Magnet |
Practice questions
- 1What is adulteration?
- 2Name two harms caused by adulterated food.
- 3How is water in milk detected?
- 4How is brick dust in chilly powder found?
- 5How is iron filings in rava removed?
- 6When was the Prevention of Food Adulteration Act passed?
- 7How many years after the 1954 Act was the 1976 amendment made?
- 8A friend says she will taste a little turmeric to check for metanyl yellow. What would you tell her, and which test would you suggest?
Show answers (try them yourself first)
- 1Removing important parts of food or adding low-quality or harmful material.
- 2Poisoning and organ damage (also cancer).
- 3A drop of pure milk on an inclined slide leaves a milky trail; watery milk does not.
- 4Put the powder in water; the red layer settles at the bottom.
- 5By passing a magnet through it.
- 6In 1954
- 71976 − 1954 = 22 years
- 8Do not taste it; add HCl: if the red colour stays, it is adulterated.
Quick revision
- Spoilage: internal factors and external contamination.
- Pasteurisation: milk at 80 °C for 15 min, then cool.
- Test iron filings in rava with a magnet.