Why do fizzy sweets make your mouth cold?

20 April 2008

Question

When I eat one of those fizzy, sugary-dextrose sweets I get a really cool sensation in is mouth [as in cold]. Is that the same as with the menthol thing?

Answer

I don't think it's the same process as with menthol because dextrose is another term for glucose - that's just sugar. I think it's in fact a clever chemical trick going on why his mouth feels cold when he sucks this sweet. I think the reason is that to make the sweets fizzy and have that effervescent effect you mix them with sodium bicarbonate which is an alkali substance with some citric acid. They're both dry but when they dissolve in your mouth the water in your mouth makes most of these dry crystals become liquids and then they can react together and you get a neutralisation reaction which has an endothermic effect. In other words it gets colder when you react an acid and an alkali together. This makes your mouth feel colder. I think it's a chemical reaction, it's one of these unusual reactions but it makes things get colder.

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