water the yolk and water can mix. Apparently, egg yolks contain some water. How much?
In order to know how much water a yolk contains, let’s carry out a simple experiment, using a balance.
One remark about this: balances can be of various kinds, but in order to measure mass differences of
the order of 1 gram, one should use a balance precise enough to display such differences. Therefore
kitchen balances with a limited precision of 10 g, or even worse 100 g can never be used!
Now the experiment: let’s weigh a yolk. The mass is about 30 g. Slowly heat the yolk in order to
evaporate the water (you could put the glass containing the yolk in an oven at 100°C), and then weigh
it again: the mass of the yolk is reduced to half the initial mass.
Hence the conclusion: an egg yolk is about 50 percent water and 50 percent other materials.
Meat and fish
Look at a piece of meat, e.g. beef. It’s red and moist. You know that you could dry it by placing it in an
oven: at a temperature of 100°C or more, water evaporates fast… which proves that meat contains a
lot of water.
How much? Just weigh a piece of meat before and after drying, and you would see that about . of
meat is water.
Just touching meat also shows that there is some fat in it: the exact quantity depends on the meat.
And finally, we all know that there are a lot of proteins. What does this mean? The answer is given in
section 4, but to begin imagine that proteins are like microscopic threads of many kinds: some are
coiled, and other have other conformations; some “coagulate” (remember egg white) and some don’t
(think of gelatine).
However, it is strange that considering meat and fish contain so much water, they do not flow. This
needs to be explained. By cooking meat for a long time in boiling water: we see that meat is
composed of fibres.
What is not shown in this boiling experiment is that these fibres are like tubes full of water and
proteins, like egg whites. “Cooking meat” means, in particular, coagulating the inside of these fibres,