August 2009

In the last post we were talking about the receptors in our tongue for the different basic tastes. On top of that, there are nerves that react to temperature (called trigeminal receptors) warning us of hot/cold food.

What is interesting is that these nerves can be activated by some molecules tricking our brain to believe that we are eating something hot or cold. For example, the molecules activating the hot sensation can be found in chili peppers, black peppers or ginger. And, guess which kind of molecules activate the cold sensation? spearmint, menthol and ethanol are some examples. This is why eating a mint causes a refreshing feeling in your mouth.

This whole business of detecting flavours is quite fascinating and is the reason of existence of this blog and thousands of recipe books but, why do we enjoy eating so much? There is of course a reason for us to detect different flavours. Salty, sweet and umami are appetitive,  and bitter and sour are aversive. Appetitive tastes drive us toward essential nutrients while aversive tastes alert us to potentially harmful substances.

One can however educate the brain and tell it that some of these aversive flavours are actually not dangerous such us coffee, olives, strong cheese, etc. This explains why children typically like food which is predominately sweet and/or acid and dislike sour or bitter tastes while adults grow into enjoying also some foods with a bitter or sour flavour.


… and umami! or “the tasty flavour”, which is the approximate literal translation. So the answer to the question in last poll was 5: the basic tastes are sweet, bitter, salty, sour and umami. If you replied 4 you are not so far from the answer because the fifth flavour was only officially added to the list at the begining of this decade.

But, what is a basic taste? Our tongue is populated with thousands of receptors that are sensible to some molecules. Up to now 5 different kind of receptors have been identified. One kind reacts for example to the presence of sugary molecules and then sends to the brain a signal informing it that we are eating something sweet. Similarly there are receptors that react to sodium ions sending a signal of something salty and other receptors react to acid and sour substances.

In the case of umami, the receptors react to glutamic acids, which can be found in protein-heavy foods such as beef, lamb, Parmesan, Roquefort, soy sauce and fish stock. As you can see it does make sense to call it the tasty flavour :).

It seems that lately there is some speculation that we might have a 6th kind of detector which would react to fatty substances. I get the feeling that this is one of those things that changes in each generation like the number of letters in the Spanish alphabet or the number of plantes in the solar system :).

Even though our tongue basically only detects 5 different kinds of molecules, our brain then is able to process this information creating a whole range of flavours, just like it can interpret a wide range of different colours from the 3 basic ones. To do this it is able to detect different concentrations of each of the flavours and also complement this information with the smell and visual input of the food.

So look, smell and enjoy your meal!

Time for another poll:

Like I did last time I will ask you not to google the answer, otherwise there is no fun in it. I want to see if we learnt the same things in school.

First of all my apologies for a long silence. This was due to an unfortunate IT problem followed by the fact that I’m travelling now and hence won’t have access to my kitchen for a while. So for the next few weeks I’ll have to rely on experiments done by other people since it is difficult to try them myself at this moment.

Back to the question, why do toasts fall jam side down? Ideas, anyone? It might seem at first sight that it is because the jam side is somehow “heavier” than the other side, but it is actually an anthropometric problem: it has to do with the size of human beings and the size of the objects we use.

Let me explain. If we let a toast fall from a high altitude say at least 2-3 meters, then it will turn around several times while falling. A good illustration of this fact is this commercial I found on You Tube:

The number of turns that the toast has time to make during its fall depends basically on the distance to the floor. The thing is that when we are eating them, we are usually sitting on a chair holding the toast in our hands so its always approximately the same distance.

Of course it also depends on the initial conditions. In the case of this commercial it will depend on whether they start with the jam side up or the nutella side up. When we are eating a toast and it falls we were usually holding it jam side up.

Another initial condition that influences the result is the angle with which it starts the fall and the starting velocity. The way this usually happens is most of the time at an angle slightly over 45º.

Finally there is the size of the toast. All of them are usually about the size of a human hand to make it easy to handle them, but if you repeat the experiment at home, say, with a huge toast, most likely it won’t have time to make half a turn from the table to the floor.

I have several proposals to solve this problem:

  • Using very high tables. Of course to make a difference the table would have to be significantly higher so probably one would have to climb up the chairs with a few steps and then there is the problem of the low roof. But it could be feasible if you have a garden.
  • Hold the toast jam side down while you spread it. If the starting condition is exactly the opposite side, the toast will fall jam side up when it falls.
  • Eat much smaller toasts or much bigger ones. The latter actually sounds good to me!

Thinking about it again, these might not be such good suggestions after all. We might just have to try to be careful and try not to drop the toast, which is very difficult for me as those who know me very well know :).

If it does fall, one can always count on the five-second rule, or not.