You probably encountered it in a biology lesson at some point: a diagram of the tongue divided into neat zones, sweet at the tip, bitter at the back, sour on the sides. Four tastes, four territories, everything sorted. Satisfying, isn't it? The only trouble is that the tongue map was wrong. The four-taste version was wrong. And the five-taste version we replaced it with might also be wrong. Food scientists are still arguing.
Most of us made it to five when umami arrived. It's the savoury, mouth-filling quality in soy sauce, Parmesan, slow-cooked meat, Marmite – that thing you can't quite name when you keep going back for another forkful. Japanese chemist Kikunae Ikeda identified it in 1908, isolated it from seaweed broth, and spent the next several decades being politely ignored by Western food science before umami was eventually accepted as a genuine fifth basic taste in the 1980s. Seventy years for the idea to land. So you'd think we'd have learned not to close the list too quickly. And yet here we are.
The current candidates banging on the door are fat, starch, and the cooling sensation of mint. Each has at least some evidence of its own dedicated receptor – and that's the thing that matters. A basic taste isn't just a flavour you notice, it's a signal your tongue sends independently to your brain. Fat, or oleogustus to give it its slightly grand scientific name, seems to have its own pathway separate from texture alone, which would explain why full-fat milk tastes different from skimmed in a way that isn't just about thickness. Starch has a decent case too. There appear to be receptors that detect long glucose chains directly, before digestion breaks them down, which would make sense evolutionarily since starchy foods are an excellent energy source and it would help your body to know that before it bothers chewing.
Mint is the oddest contender. The cooling sensation comes from a compound called menthol activating the same receptor (TRPM8, if you want to impress someone) that your skin uses to detect cold. So your mouth isn't being cooled, it's being tricked – and whether that counts as a taste or just a very convincing lie is exactly the kind of question food scientists enjoy arguing about in conference rooms.
What's interesting is how much of this maps onto the problem explored over at The Theory That Refuses to Die: the way a compelling, organised framework can keep its grip on people's thinking long after the edges have started fraying. Five tastes is a tidy system. It has the feel of a complete answer, and that feeling of completeness makes it very hard to update, even when you keep finding things that don't quite fit.
Which is probably why the next time you eat a bag of ready salted crisps and can't stop, you might be responding to fat receptors nobody officially accepts yet. The science just hasn't caught up with your hand reaching into the bag again.
