Why cucumber with sugar tastes of watermelon

A recent TikTok video features this food experiment. It's not a mystery though, thanks to flavour chemistry.....
18 February 2021

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Cucumber slices.

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This claim has surfaced on TikTok: if you put sugar on cucumber, it tastes like watermelon! It's partly true, but it's not a mystery - thanks to the magic of flavour chemistry...

Not everyone agrees - Dotty MacLeod on BBC Radio Cambridgeshire certainly didn't - but for others, sugary cucumber tastes a lot like watermelon.

Perhaps it’s not that surprising! Watermelons and cucumbers come from the same family of plants: the gourd family, also called the cucurbits. Alongside them sit squash, pumpkin, various other melons, and even loofahs for loofah sponges!

Both cucumber and watermelon are full of water. Cucumber has the highest water content of any food, at 96%; with watermelon clocking in close behind at 91%.

Plus, sharp-nosed people can tell that - depending on the variety - cucumbers already have a mild melon-like smell and taste.

This comes from compounds called aldehydes. There’s a particular aldehyde called trans,cis-2,6-nonadienal that's found in both cucumbers and melon, and this could be the crucial component.

The Good Scents Company describes trans,cis-2,6-nonadienal's scent as “green, cucumber, melon, fatty and rindy with a hint of meat fat.”

Interestingly, trans,cis-2,6-nonadienal is easily broken down, which is partly why you never get watermelon sweets that taste like actual watermelon.

Flavour compounds are funny things…

You perceive a food’s flavour from both your taste buds and your sense of smell (as well as texture, temperature, and other factors such as minty coolness or chilli spiciness).

In the case of cucumber and watermelon, it seems like the smell part is already similar thanks to trans,cis-2,6-nonadienal. Adding sugar aligns the taste part too.

Why is a single compound so crucial? Natural flavours normally involve a complex mix of smell molecules interacting. But many of them, particularly strong fruit ones, involve one or more dominant compounds - as in this case.

These are often from a family of compounds called 'esters'.

Sometimes these esters can be strangely versatile. The flavour of artificial banana sweets comes from an ester called isoamyl acetate. If you smelled it on its own, you'd instantly recognise the smell of banana. But add water, and it smells more like pears; so it’s also a key ingredient in pear drops.

All of which is to say that artificial flavours, which may rely on single compounds like these, can do strange things when you put them in different combinations.

Supposedly, if you take a random handful of jelly beans and eat them, they almost always taste like a single, unexpected flavour. A delicious experiment to try at home!

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