General Knowledge
Why do onions and apples taste alike if you hold your nose?
- Most of taste is actually smell
- They contain the same sugar
- Your tongue is confused
The answer is Most of taste is actually smell. Flavour is mostly smell; the tongue detects only a handful of tastes.
Because almost everything you call taste is smell. The tongue detects five things - sweet, salt, sour, bitter and savoury - and everything else comes from volatile compounds reaching the nose from the back of the mouth as you chew, which is why food is flat during a heavy cold.
Onion and apple are the classic pairing for the trick because their texture and their sugar and acid balance are close enough that removing the aroma leaves very little to tell them apart. Raw potato works too. Wine tasters exploit the same route in reverse, breathing out through the nose deliberately.
It also explains a stubborn confusion about spicy food. Chilli heat is not a taste at all - it is the pain system, triggered through a heat receptor - and neither is the cooling of mint, the astringency of strong tea, or the fizz of carbonation, which is detected as mild acidity. A tongue map showing regions for each taste was drawn from a mistranslated German paper in 1901 and is wrong; all five are detected across the whole tongue.