askST: Why does chopped garlic have a kerosene smell and taste?

Reader Polline Teo wrote in to ask about storing garlic.

She said: "I was a working mother until I recently retired in 2015. To expedite cooking dinner, I would grind all my garlic into a bottle, pour olive oil and salt into it, and it would be ready for use. The smell of garlic was beautiful raw as well as fried.

"Lately, I noticed the ground garlic - both raw and fried - has a kerosene smell and taste. It seems you cannot store it, but should use it daily. As such, I have avoided using garlic in my dishes and have thrown out all the prepared garlic."

Food writer Eunice Quek finds out.

A spokesman from the Agri-Food & Veterinary Authority (AVA) says: "Garlic is rich in sulphur. Its characteristic flavour and smell is caused by volatile sulphur compounds which are released when garlic cells are ruptured by actions such as chewing, chopping or crushing.

"Garlic - crushed, chopped and stored in any form - should not smell or taste like kerosene. The complexity of odour from the volatile compounds, especially when mixed with oil, may give rise to the perceived 'kerosene' smell and feel. If unsure, do not consume the garlic."

Ms Bibi Chia, principal dietitian of the Raffles Diabetes & Endocrine Centre, recommends that garlic in oils "must be frozen or refrigerated", and it should not be stored at room temperature.

The AVA spokesman adds that raw ground garlic mixed in oil - stored at a temperature high enough for bacteria to grow - provides an ideal environment for clostridium botulinum, a bacterium known to produce toxins which can cause fatal food poisoning.

For whole garlic, it is best stored in a cool, dry and well-ventilated place, to minimise sprouting and mould growth, says the spokesman.

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