In the six months that this blog has been alive the most viewed post is by far the one when I talked about putting chocolate in the fridge. Which shows that this is a very controversial topic. So I would like to know what your opinion is: do you like putting chocolate in the fridge, yes or no?

In that post I argued that one shouldn’t put chocolate in the fridge because it spoils both texture and flavor. Texture especially in the case where one puts chocolate in the fridge after it has been partially melted by heat: it does not go back to the “good” crystalline structure that it should but to another one with different properties. And flavor because it absorbs moisture and odours from other food stored in the fridge. But since this is so polemic perhaps many of you still prefer to eat your chocolate chilled despite these disadvantages. I’m very curious to see which option wins so help me out and participate in the poll.


In the past weeks I have been away from my kitchen again, which has slowed down my posting. I still didn’t have a chance to make new experiments but I found this nice video explanation of “why does cream whip” which I found quite illustrating. So instead of doing an experiment my self, in this occasion I just recommend you to watch that video.

It is from the website of “Bang Goes the Theory”, a new BBC program about science for a family audience. The first season is already over, but if you like it you’ll be able to get more of it in March when it will come back for a second season.

There are many urban legends in the kitchen: adding salt to water makes it take longer to boil, applying hot temperature to fish and meat “seals” the juices inside, the five-seconds rule, etc. Being in Japan I am concerned with a myth related to raw fish. The thing is that I’m no sure whether it is a myth or not, so I’m hoping one of you can offer some insight on this topic.

A few years back, there was a big media wave in Europe about anisakis. This is a parasite that lives (mainly) in fish intestines, but also sometimes in their muscle or below the skin. When an infected fish is eaten by a human, this parasite can infect the person causing abdominal pain, fever, nausea, vomits and diarrhea. Sometimes the individual can then become allergic to anisakis and a second ingestion of the parasite (even if dead, that is even if the infected fish has been cooked) could cause a violent allergic reaction. I personally know people who have had anisakiasis and at least one person who has become allergic to it.

It seems like the most effective ways of avoiding this is to kill the parasite by either cooking the fish (for at least one minute at temperatures higher than 60ºC or for at least 15 seconds if temperature is higher than 74ºC) or freezing it to -20ºC or lower for at least 24h). Other forms of preserving fish like in salt or vinegar do not kill the parasite. For this reason in Europe, and also in many other countries outside of Europe, it is now compulsory to freeze fish that is going to be served raw.

Wild fish is more likely to be infected with anisakis than farmed fish and also cleaning properly the fish before eating it and getting rid of the intestines  soon after the fish has been capture both reduce the risk of ingestion of the parasite (although it does not eliminate it completely).

The incidence of anisakiasis has increased a lot in the past few years due to several factors:

– The anisakis population is increasing in part due to the bad habit of throwing fish remains back to the sea after consumption.
– The increasing consumption of raw fish in the world.
– Improvement of diagnostic techniques. In fact, until the 90s, most anisakiasis cases went undiagnosed because of the similarities with other indigestion episodes and seafood allergies.

Now I am in Japan and here it is not compulsory to freeze fish before serving it raw. In fact, wild fresh fish is highly appreciated and more expensive than farmed fish or fish that has been frozen. So the question is, is it safe to eat raw fish in Japan? After doing some research on-line, I have found the following arguments in both directions:

– Yes, it is. Because Japanese people have been eating raw fish for centuries they know how to prepare it properly and clean it very well. Also, they usually it raw fish with wasabi which has the property of killing parasites (I found no satisfying reference for this claim, is it an urban legend?). In other countries it is less safe to eat it because they don’t clean it well and sometimes they don’t serve real wasabi with it but just a coloured version of horseradish mustard.

– No, it is not. It is estimated that 95% of the world occurrences of anisakiasis happen in Japan, with an average diagnosed rate of incidence of at least 1000 cases per year. By far, they are the most affected country by the disease, showing that they do have a problem.

I’m starting to think that fresh raw fish is too internalized in japanese culture to have a law forcing them to freeze it before consumption. After all, most cases of anisakiasis are not live-threatening.

What do you guys think? Do any of you know where to find more accurate information about this? Any contributions will be greatly appreciated, especially because I have been eating sushi and sashimi here in Japan for the past months and it is indeed delicious!


PUmpkin cookie

You might have noticed that I’m without a kitchen again. Fortunately, people around me still do have kitchens and yesterday I got this nice pumpking cookie. The only connection with science in this case is that it was cooked by members of the staff of a scientific institute in Japan (where I am now).

Today I want to talk about salt. What we call salt in the kitchen is different to other uses of the word salt. For example, for chemists it is an “ionic compound” of different elements. This is why they have salts in all possible colours. We call bath salts a range of different products that can be dissolved in water before we take a bath, etc. But in gastronomy what we call salt is just good old NaCl.

Now, if salt is salt, that is NaCl, how come different salts taste different? And how come in the supermarket shelfs there is an increasing number of different kinds of salt each of them is more and more expensive?

Personally, since I live in the UK, I find that table salt is the dullest of them all. Back in Spain the most common salt in a supermarket is sea salt, so I had not used table salt before. I found that I had to use much bigger quantities of table salt to obtain the same effect that I did with sea salt and yet, it was never quite the same.

Initially I thought this was perhaps because the cheap table salt was not pure salt but perhaps had some impurities in it that made necessary to use more quantity of it while cooking. I was surprised to discover that it is quite the opposite: table salt is the purest of them all. Table salt is refined until it contains a percentage of NaCl of between 97% and 99%. Sea salt, on the other hand contains typically around 90% of NaCl and the rest is sulfate, magnesium, calcium, potassium, bicarbonate, bromide and some other elements in very small quantities.

So what makes sea salt different and gives it a flavour that I personally like more (and it seems from what I read that most gourmets agree with me) are precisely those elements in it which are not salt: its defects.

There is much more to the world of salt than just table salt or sea salt and some of its other shapes are quite expensive as well. The difference between them is not only in the flavor because of their impurities but also sometimes in the texture. Salt comes in little crystals. These crystals can be very thin (salt flakes) or very big (like for example in Maldon Salt). The thin ones  melt instantly in your mouth giving the feeling of a very smooth flavour while the Maldon rocks give that nice crunchiness. Of course one can only notice this when the salt is added just before serving and it does not have time to melt before it gets to your tongue. If you pour Maldon salt or salt flakes in the water while doing pasta you won´t notice the difference then.

Recently I learnt about a kind of salt that I had never heard of “Fleur de sel” or salt flower. Only a few days a year in the very early hours of the morning a thin layer of salt is formed on the top of the water in some salt plants. These layers are manually harvested before they sink back to the bottom after the sun rises and sold at high prizes in airtight jars while still slightly dump. It has two attractive properties: on the one hand it has a high contain of some minerals that give it a very special flavor. On the other, the structure of the crystals is so thin and delicate that they dissolve instantly in your mouth.

I came a cross some “Fleur de sel” in my supermarket recently:

Flor de Sal (Fleur de sel)
Flor de Sal (Fleur de sel)

Unfortunately they didn´t have the plain one but only this one which is flavored with olives. I used this salt, sea salt and table salt in different parts of a Caprese salad (tomato and mozzarella) and I have to say it was delicious!

Capresse with different kinds of salt
Caprese with different kinds of salt

I could notice the difference in flavour between the three: my favorite being the Fleur de sel and the one I liked the least table salt. However to compare properly I would have liked to use plain salt flower, rather than the olive flavoured one. Also, the texture was remarkable, it was certainly the smoothest salt my tongue has ever felt.

I highly recommend doing this experiment at home. Take different kinds of salt from the supermarket, pour them onto different parts of a salad or a stake and feel the difference. What is your favorite one? Perhaps you like one better on meat but another better on the salad? Mastering which salt to use for each particular dish is a very difficult task, but using 2 or 3 different kinds of salts in your cooking will surely improve your dishes and impress your guests.

Embrace the defects!

A good friend of mine has introduced me to Kevin Van Aelst. This young photographer has very interesting pieces, some of which are somehow in the complement of this blog. If here we try to use science to explain food, these photographs use food to explain science. Here are some examples:

Common Clouds

Common Clouds


Cantor Set

Cantor Set

Fingerprints Pie

Gummy bears Periodic Table

Gummy bears Periodic Table

Logarithmic Sprial

Logarithmic Sprial

Cellular Mitosis

Cellular Mitosis

When you boil an egg you will see how often a greenish layer appears surrounding the hard boiled yolk. This is a sulfur and iron compound called ferrous sulfide. It is formed when the iron present in the yolk and the sulfur contained in the white meet at the surface of the yolk at high temperatures reacting and forming this compound.

The sulfur in the white is attached to a protein and only released in the form of a gas at high temperature. Then this gas diffuses through the egg and it is when it meets the iron in the yolk that they form this green layer.

This sulfur gas is responsible, in small quantities, for the pleasant smell of cooked eggs but, in larger quantities, it is the odor we associate with rotten eggs.

The way to minimize this layer forming is to keep the sulfur gas from reaching the surface of the yolk. This can be done in two ways. First, we can avoid it forming at all by cooking the egg at lower temperatures. We need the water to be hot enough so that the egg will cook but not so hot that this gas will be released in big quantities. This means keeping the water at around 85º-90º (185 F-190 F), that is slightly below boiling point. The second thing we can do is avoiding the gas reaching the egg yolk. We can slow the gas down by cooling it, this is, putting the egg under cold water as soon as it is cooked.

I did the following experiment. I cooked one egg in boiling water for 15 minutes and then did not put it under cold water immediately but rather let it cool down slowly. Then I put another egg in boiling water but with the fire turned off so that the water quickly cooled down. I added regularly boiling water to it so that the mix would be hot but under boiling point. I kept doing this for 30 minutes and then cooled down the egg by quickly putting it under cold water. This was the result:

Yellow and green yolks

Yellow and green yolks

The left yolk is the one that was cooked at a temperature lower than the water’s boiling point and the right one was cooked in boiling water. As you can see the green-greyish layer is not present in the egg cooked at a lower temperature.

Depending on what you are cooking it might not be worth going through the hassle of boiling eggs like this, but if you want to present pretty shinny yellow yolks you know what to do :).