Science Questions

Can we taste without smelling food?

Can we taste without smelling food? I'm wondering whether we can taste without smelling food because yesterday, I had a blocked nose and onion tasted like potato. Tejas Rode, Bristol

Helen: -    Wow!  It’s really good question and you've hit on the right point that it’s not just about our taste in our mouths.  It’s also our nose that leads to a sensation of flavour and taste, and we have two things going on.

We have our tongues which have taste buds on them, in little ridges and valleys called papillae, and these are responsible for picking up the four and some people think five main tastes which are bitter, sweet, sour, salty, and savoury or ‘umami’.

There’s not much nuance to those different flavours, but we do pick those up in our tongue, and the rest of the taste that we have comes from smelling the food, from the odour molecules that come off it.  They waft up our nose and essentially, fire nerves signals from somewhere called the olfactory mucosa inside your nose which has receptor neurons and they will tell your brain when you've picked up certain different chemicals in the food.

But interestingly, it’s not all the smell that comes up your nose that is responsible for the taste.  So the reason you can't smell when you have a cold is because your olfactory mucosa gets covered in goo and those receptor neurons really don't get anywhere near to those molecules of odour that they're interested in.  But if you hold your nose, you might have noticed you can still taste quite well when you're eating, and that’s because some of those molecules also go from your mouth through the internal passages, and still find their way to the olfactory mucosa. 

So it’s no good just holding your nose if you don't like the taste of your medicine.

Chris: -   I used to do that.  The medicine for Brussels sprouts actually.

Helen: -   It does help and interestingly, in a 2005 study in the journal Neuron, Dana Small from Yale University led a study where they put tubes up volunteers’ noses.  (I hope they did pay these people well because it does sound like a fairly nasty study.)  One of the tubes went just to the nose.  The other one went back into the mouth and they wafted smells up these different tubes.

They put the people inside an MRI scanner, and showed that different parts of the brain were activated depending on if the smell went to their olfactory mucosa directly or whether it went into the mouth and then sort of wafted back up there. 

It makes sense that essentially, if you're smelling something from a distance, it’s more like, “Oh goodie, there’s some chocolate on the way.  Perhaps I should go find myself some of that.”  Whereas if you're eating the chocolate, you're actually doing other things like preparing your body for a nice hit of fat and sugar that’s going to come along with this chocolate that you're eating.  So it seems something quite interesting is going on in your nose and your mouth to lead to the sensation of taste.

Chris: -   Terrific.  I still say holding your nose works well for Brussels sprouts.  It did for me.

June 2010