Q1.
Mystery #2: Why do some foods spoil faster? — “Strange!”, whispered Disha. “Why does some food spoil fast, and some last for a long time?”
Answer
A food spoils fast when microbes can grow easily on it, and lasts long when something is stopping them. The slice of bread on the balcony had everything microbes need — moisture, air and warmth. The pickle did not, because it was covered with oil.
| The bread on the balcony | Paati's mango pickle | |
|---|---|---|
| How long it lasted | Spoiled in two days | Still good after two months |
| Moisture in it | Soft and moist | Salt has pulled the water out of the mango pieces |
| Air reaching it | Lying open in the air | A layer of oil on top keeps the air out |
| Anything stopping microbes? | Nothing at all | Salt, spices and oil all make it hard for microbes to grow |
| Result | Coloured patches of mould | Still delicious |
The rule in one line: foods that are wet, soft and left open spoil quickly; foods that are dry, salty, sugary, oily, cold or sealed last a long time.
Moisture + air + warmth = microbes grow → food spoils fast
Take away any one of them = food lasts longer
Take away any one of them = food lasts longer
Why the oil works: Oil and water do not mix, and oil is heavy enough to sit as a layer on top of the pickle. Microbes below cannot get the air they need. So they simply do not grow.
Try this ranking: milk and cooked rice spoil in a day; bread and fruit in two or three days; a boiled-and-cooled dry ladoo in a week; papad, chilli powder and pickle last for months. Notice how the amount of water in each one goes down as you move along that list.