Молекулярная гастрономия для креативных шеф-поваров (англ. язык) - страница 213

Молекулярная гастрономия для креативных шеф-поваров (англ. язык)

In the previous experiment, we did not discuss the main point that heating the egg white makes it turn

white. Isn’t it truly remarkable that a yellow material turns white on heating! Why? And isn’t it wonderful

that simultaneously on heating, a liquid material turns solid? Why?

Remember that an egg white is mainly composed of water: therefore the question of its hardening on

heating is even stranger!

A simple reasoning helps. When you heat pure water, it doesn’t solidify, but when you heat a mixture

of water and proteins it turns solid. This means that proteins are responsible for the solidification. But

proteins do not always cause solidification: heating a solution of gelatine dissolved in water does not

make a solid.

This simple observation makes us conclude that there are proteins of various kinds.

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Another question, at which temperature does the egg white solidify, or “coagulate”? Again, another

experiment helps.

Experiment

In order to know at which temperature egg white coagulation occurs, let’s begin by a crude

experiment. Put some egg whites in a drinking glass, and place the glass on a stove, heated by the

bottom.

Slowly coagulation begins at the bottom of the glass, and the limit between the lower coagulated layer

and the upper liquid layer rises up.

Use a thermometer to measure the temperature over and under this limit (or “interface”): you can

observe that coagulation occurs between 60 and...

e a thermometer to measure the temperature over and under this limit (or “interface”): you can

observe that coagulation occurs between 60 and 70°C. No point using boiling water –at the

temperature of 100°C- to cook eggs: 70°C is enough!

And, please, have a look to the consistency of coagulated egg white, from the bottom of the glass up

to the interface. What can you see?

Let’s now move to yolks. It is sometimes said that the yolk contains “fats”, but is it true? If you add

some oil to water, it does not dissolve, but if you add water to water, it dissolves well. Adding a small

quantity of oil to a ruptured yolk (remember that the membrane that would otherwise prevent mixing

has to be pierced) shows that the oil does not dissolve in the yolk; but after adding a small quantity of

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