Usually I find it easy to resist reality TV, but not the Great British Menu. I just get sucked in and then have to know who will score highest on the courses, and then who wins on the Friday. I really don’t think this has anything to do with the science on show in the cooking, I just start rooting for the chefs as they try so hard to make their elaborate dishes.

However, there is loads of science in cooking, and this is made explicit in molecular gastronomy. It is the sort of science I know something about as it is close to my research field of ‘soft matter’.

This week one of the chefs used the technique called spherification. Basically how this works is you start with a tasty liquid, the chef on the Great British Menu flavoured it with peas. You then mix this liquid with sodium alginate. Now alginate is a polymer (derived from algae, hence the name), i.e., the molecules are very long and floppy. It is also negatively charged. That is why you need the positively charged sodium ions to make the solution electrically neutral overall.

Now each sodium ion has only a charge of +1 (in units of the elementary charge, the magnitude of the charge on the electron). This is important because if you get a sodium ion sandwiched between bits of two alginate polymers it attracts both of them and so tends to stick them together. But only weakly as it only has a charge of +1.

So, the chef then drops a droplet of  the pea-flavoured liquid containing sodium alginate into a bath of water containing calcium ions. Calcium ions have a charge of 2+. When an ion is sandwiched between two alginate polymers then doubling the charge to 2+ greatly increases the attraction. So the 2+ calcium ions stick the alginate polymers together into a mesh.

This mesh is a gel and the calcium linked alginate polymers transform the liquid into a soft solid gel. I guess that the calcium ions mostly diffuse in from the surrounding calcium solution into the initially liquid pea-flavoured droplets. This is not very fast so the chef can remove the pea droplets from the calcium solution quickly while only the surface layer is made jelly-like by the calcium ions replacing the sodium ions.

The result is a droplet with a soft jelly-like shell and liquid inside, tasting of peas or whatever the chef wants. Spherification was apparently pioneered by the restuarant elBulli. For several years this was often listed as the world’s best restaurant. It closed last year. I think it must have been a serious restaurant, the Wikipedia page claims it charged £200/meal and still managed to make a loss! McDonald’s it ain’t.

It is really impressive seeing science being applied in this way, you do not have to look up to the stars to admire science, you can look down to your dinner plate.