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How do roast potatoes stay so hot for so long? © Getty Images

How do roast potatoes stay so hot for so long?

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The science behind your burnt mouth during Sunday roasts.

It’s mostly to do with the fatty, starchy crust that acts like an insulating layer. First, pre-boiling a potato causes its starch granules to absorb water and swell until carbohydrate molecules seep out to create a kind of thick gel.


The high temperature in the oven then drives off moisture, causing the gelatinised starch on the outside of the potato chunks to form a crispy crust, trapping the heat inside. The fat from the baking tray also collects in cracks and crevices and strengthens the heat-keeping structure.

Asked by: Sarah Fullerton, London

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Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.


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