The Mystery of Food — NCERT Solutions

Given: Drying removes moisture, and without moisture microbes cannot grow.

Things that are dried to remain unspoilt throughout the year include:

1. Papad – dried in the sun before storing.
2. Dry fruits (raisins, dates, figs) – moisture is removed so they last long.
3. Fish – dried and salted to preserve for months.
4. Spices (coriander seeds, cumin, turmeric) – dried before grinding or storing.
5. Amla (Indian gooseberry) – dried to make dry amla candy.
6. Tomatoes – can be sun-dried and stored.
7. Grains and pulses (wheat, rice, dal) – dried thoroughly before storing in sacks.

Conclusion: Drying is one of the oldest and most common methods of food preservation because it takes away the moisture that microbes need to survive and grow.

Given: Mangoes are a seasonal fruit and need to be preserved to enjoy them for longer.

Items that can be made from mangoes for longer enjoyment:

1. Aam papad – dried mango pulp sheets.
2. Mango pickle (Aam ka achar) – raw mangoes preserved in oil, salt, and spices.
3. Mango jam – cooked with sugar and stored in jars.
4. Mango squash / juice – bottled and stored.
5. Dried raw mango powder (Amchur) – raw mangoes dried and ground into powder.
6. Mango chutney – cooked with sugar, vinegar, and spices.
7. Canned mango pulp – sealed in cans to preserve freshness.

Conclusion: By using methods like drying, pickling, cooking with sugar, and canning, mangoes can be enjoyed long after the season is over.

(a) Observations after placing tomato slices in sunlight:

• The tomato slices gradually lose their moisture and shrink in size.
• The colour changes from bright red to a darker, deeper red.
• The texture becomes dry, leathery, and wrinkled.
• The slices become lighter in weight.
• After complete drying, they do not spoil easily because microbes cannot grow without moisture.

(b) Ways to preserve tomatoes:

1. Sun-drying – Slice and dry in sunlight to make dried tomatoes.
2. Making tomato puree or paste – Cook and seal in airtight jars or cans.
3. Refrigeration – Store fresh tomatoes in the fridge to slow down spoilage.
4. Making tomato sauce/ketchup – Cook with sugar, salt, and vinegar; bottle and seal.
5. Freezing – Blanch and freeze tomatoes for later use.

Conclusion: Removing moisture through drying is an effective way to preserve tomatoes, just like chillies.

Given: Oil keeps out air and stops the growth of microbes (Finding #4).

If no oil had been added to the pickle:

1. Air would enter the jar and come in contact with the pickle.
2. Microbes (bacteria, fungi) need air to grow; without oil as a barrier, they would grow rapidly on the pickle.
3. The pickle would spoil quickly – it would develop a bad smell, change colour, and become unsafe to eat.
4. Mould (fungus) might appear on the surface of the pickle.
5. The pickle would not last for months or years as it normally does.

Conclusion: Oil acts as a protective seal that blocks air, thereby preventing the growth of microbes and keeping the pickle safe and tasty for a long time.

Given: Cold temperature slows down microbes (Finding #5). The hint tells us to compare how butter and ghee are made.

How butter is made: Butter is made by churning cream. It still contains water/moisture in it.

How ghee is made: Butter is heated on a flame. The water evaporates completely, leaving behind pure fat. This is ghee.

Reason:

• Butter contains moisture (water), which allows microbes to grow. Therefore, it needs to be kept in the refrigerator (cold temperature) to slow down microbial growth and prevent spoilage.
• Ghee has no moisture at all – all the water has been evaporated during the heating process. Without moisture, microbes cannot grow. Therefore, ghee can be stored at room temperature without spoiling.

Conclusion: The presence of moisture in butter makes it perishable and requires refrigeration, while the complete absence of moisture in ghee makes it shelf-stable without refrigeration.

Sample Answer (students may write their own family practice):

Food Preservation Practice in My Family:

My grandmother makes raw mango pickle (Aam ka achar) every summer. She cuts raw mangoes into pieces, mixes them with salt, turmeric, red chilli powder, mustard seeds, and fenugreek seeds, and then pours mustard oil over them. The jar is kept in sunlight for a few days and then stored at room temperature.

Why it works: Salt draws out moisture from the mango, oil seals out air, and spices have natural antimicrobial properties. Together, these methods prevent microbes from growing, and the pickle lasts for an entire year.

*(Note: Students should write the actual practice followed in their own home, as observed by asking their elders.)

Sample Answer:

Finding #9 (by student):

"Fresh vegetables and fruits should be firm, brightly coloured, and free from spots, cuts, or bad smell. These signs tell us that the food is healthy and has not started to spoil."

What I learnt from my shopping trip:
When my grandfather buys vegetables, he always presses them gently to check if they are firm. He smells fruits to check their freshness. He avoids vegetables that have soft spots, wrinkles, or a bad odour because these are signs that microbes have already started to spoil them.

*(Note: Students should write their own genuine observation from a real shopping trip with their elders.)