Gone off

The idea

When fats and oils are oxidised they become rancid, and their smell and taste change.

The old packet

A packet of chips (fried in oil) is left open for a long time. When you taste it, the smell and taste are not nice any more.

Why has the food changed?

• The fats and oils in it have reacted with oxygen in the air
• The chips have lost their salt
• The oil has turned into water

Four ways to keep chips

Press Play. The same chips are kept in four different ways. Watch their colour and smell.

Oxidised fats go rancid

When fats and oils are oxidised, they become rancid and their smell and taste change.

Chips makers flush bags of chips with a gas such as nitrogen so that the chips do not get oxidised.

• Way to protect | What it does
• Antioxidants added to the food | substances that prevent oxidation
• Airtight container | slows down oxidation
• Flushing the bag with nitrogen | chips do not get oxidised

Notes

When fats and oils are oxidised they become rancid, and their smell and taste change.

Check yourself

What happens when fats and oils are oxidised?

Why do chips makers flush bags with nitrogen?

Which one slows down rancidity?

• They turn into water. Oxidised fats turn rancid. They do not become water.
• They become rancid: smell and taste change — correct. Yes! The food has gone off.
• They become sweeter. The smell and taste get worse, not sweeter.
• To make the bag heavier. The gas is there to protect the chips.
• To make the chips salty. Nitrogen has no taste. It protects the chips.
• To stop the chips from getting oxidised — correct. Yes! Without oxygen the oil cannot be oxidised.
• Keeping food in an airtight container — correct. Yes! Less air means slower oxidation.
• Leaving the packet open. More air means faster oxidation.
• Spreading the food out in the open air. More air touches the food, so it oxidises faster.