The Science of Skimming

The CC would like to talk a little bit about the science of immiscible liquids, and how it applies to cooking.

Basically, oil and water are immiscible. Also, oil is far less dense that water which means that if you slowly pour oil into water, and wait for a while, all the oil will rise to the surface.

This is precisely what makes vinaigrettes so unstable. Over time, the oil and the vinegar separate out.

(And no, the CC is not going to talk about the theory of statistical mechanics that makes this happen. Not unless he is drunk in which case he bears the right to pontificate about all kinds of scientific and cooking topics.)

Suffice to say, that a gentle heat speeds up this process of separation (more molecular kinetic energy for the science types.) However, extreme heat (in the form of boiling,) or extreme shaking (which is the same thing science-wise) breaks up the two liquids into small drops which then appear to mix (emulsification.)

Please note that the two liquids haven't really mixed. They are giving the appearance of having mixed, and will separate out once again if left alone (again, think vinaigrette.)

So a very slow heat that prevents boiling will allow all the fat to come to the surface from which it may be skimmed off.

A reader of this blog was very surprised when she clearly saw the two liquids separate when the CC made dinner, but it's elementary science not magic.

However, the trick, as always, is very very low heat, and patience. Sadly enough, in the modern world, the latter seems to be in short supply.