Rancidity
- CBSE · NCERT Class 10, Ch 1 Chemical Reactions and Equations
Rancidity is the change in smell and taste of food containing fats and oils when those fats and oils are oxidised by air.
Rancid food has gone stale in a chemical way. Oxygen in the air reacts with the fats and oils. This is oxidation, the same kind of change that makes iron rust.
So the ways to slow it down all keep oxygen away from the fat:
- Add antioxidants, substances that stop oxidation.
- Keep food in airtight boxes.
- Fill packets with a gas such as nitrogen, which does not react with the food.
A small example
Take 2 packets of fried chips. One is opened and left on a shelf for some days. The other stays sealed, full of nitrogen. The open one meets air every day, and its oil slowly oxidises. It starts to smell and taste odd. The sealed one keeps its taste, because its oil has no oxygen to react with.
Where marks go
Question 22 of CBSE's 2026-27 Science sample paper shows a biscuit label with E304 and E307b. It asks what else is added to food packets for the same reason. The 2026-27 Science marking scheme gives the answer as nitrogen, and notes that E304 and E307b are antioxidants.
It is a 1-mark choice question, so there is no part credit. The mark depends on linking the label to one idea: stopping oxidation. Read where the marks go in CBSE Science.
Sources
Facts last checked against these sources on 30 September 2026.
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