Bartoshuk remembers her very first experiment into these lingering after-effects. She put various fluids on people's tongues and then gave them water to see what happened: some of her subjects were certain the second fluid was flavoured with particular acids or sugars. “It was very funny, because all of the stimuli were water,” she says.

Curious orange

The culprit in the case of the toothpaste and orange juice is a detergent called sodium lauryl sulphate (SLS) that foams when you're brushing your teeth. Detergent molecules like SLS have chemical properties that let them elbow their way into bubbles of fat molecules and disperse them. That's all fine and good when you're using dish soap to wipe spaghetti bolognese off the dinner plates. But the membranes of our biological cells are also made of fats. The current theory is that SLS somehow tampers with the membranes of the taste cells on our tongue. “It not only reduces your ability to taste sweet, it tends to add a bitter taste to acid,” says Bartoshuk. So when you drink orange juice under the influence of SLS, you taste none of its sweetness and its tartness comes across as bitter.

There’s a more direct way to briefly knock out your sweet taste, says Bartoshuk: just suck on a pill containing the Indian herb Gymnema sylvestre – sometimes known as the sugar destroyer. It knocks out your sweet receptors for about half an hour, meaning the tastes normally masked by sweetness jump out at you.

Recently, after eating a camembert-style cheese, I found an apple tasted awful, kind of soapy and bitter. Could something in the cheese have disabled my sweet receptors? Bartoshuk suggested an experiment – try the apple after some Gymnema and see if it has the same effect as the cheese.