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Why does adding salt to pineapple make it sweet?

Why does adding salt to pineapple make it sweet? Someone told me that table salt should not react with the acid in the pineapple.

Pineapple not sweet enough? Then reaching for the salt shaker may not be such a bad idea.

But why the pineapple then tastes sweeter may have more to do with what's going on in our head than what's going on in our food, thanks to the complexities of our sense of taste.

"We only have five tastes: sweet, sour, salty, bitter and umami [savoury]," says sensory scientist and qualified chef Dr Russell Keast from Deakin University.

Sounds simple enough until we start looking at complex foods that are composed of multiple tastes, like pineapple.

How salt can make pineapple sweeter "comes down to interactions between tastes" says Keast, but it's not a straightforward process.

In this case we're looking at how three different tastes — sweet, bitter and salty — interact.

To start with, bitter and sweet tastes can mutually suppress each other. A simple example of how this works is when you add sugar to coffee. As well as making the coffee sweeter it also reduces its bitterness.

"It's the way we process the flavours," says Keast. "The signals are still going up to the brain, the brain perceives sweet and bitter, and mutually suppresses both flavours."

So while the coffee is sweet and bitter, it tastes less sweet and less bitter to us because of the way our brain cancels out some of the sweet and bitter tastes coming from our tongue.

Into this situation we then add salt.

Common table salt is primarily made of sodium chloride and sodium is a very good bitterness inhibitor, meaning it can reduce the bitter taste of foods it's added to.

So when you add salt to pineapple the sodium actually reduces the bitterness of the pineapple, says Keast.

"This is something that is happening at a tongue level," he says. "The signals are not going through to the brain."

And if you don't have this bitter signal going through to the brain, it can't be suppressing the sweet flavour.

So with some of the bitterness being removed by the salt, that means there is less bitterness to suppress the sweetness of the pineapple and voila — your pineapple tastes sweeter!

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Sweet chemistry

Food scientist Dr Hannah Williams from Curtin University of Technology says there may also be another mechanism at play.

When the sodium chloride dissolves into the pineapple it will break apart into sodium and chloride ions.

The sodium ion will then react with the malic and citric acids present in the pineapple to form neutral sodium salts.

Acids normally have a tart or sour taste but when they are converted into neutral compounds they lose this sourness, and so the pineapple tastes sweeter.

Dr Russell Keast and Dr Hannah Williams were interviewed by Suzannah Lyons.