layer, and part of the bottom layer. These two parts of the milk are clearly different. The upper part is
cream, and the lower part is milk.
The main difference? The fat content! You can taste it, and you can even look at it using a
microscope: you will then see that the “fat droplets” in cream are much more “packed” than in milk.
Like milk, cream is an emulsion, but it has a much higher fat content.
One word about “oil” and “fat”: in the context of emulsions, and more generally in systems called
“colloids”, liquid fat is called “oil”. Of course, there is not corn oil in milk, but there is some fat. And the
emulsion is called “oil into water emulsion”.
How about making butter? You have certainly done it before: just churn cream, and you will get two
parts: butter, and also some liquid called whey. This means that butter must contain less water than
But it does not show (again here a microscope would be useful) that the physical structure of butter is
no longer an emulsion: fat droplets have fused together to form a continuous structure, made of solid
and liquid fat, and this structure includes some water droplets.
Clarifying butter (by heating) destroys this structure, and causes the water to fall to the bottom, and
the liquid fat to float on top.
And if you want to make butter again from the two “phases”? Just whip the cooled but still soft clarified
butter and add the water to it during whipping.
And finally, do not forget that cream and butter are cousins. Chefs sometimes experience the problem
that whipped cream turns into butter: this is of no surprise, because butter is obtained by whipping
cream for a long time.
This observation also gives a solution to the problem of whipped cream turning into butter: just melt
the “butter”, and whip it again while cooling. If the overall structure is completely destroyed, you would
have to completely melt the system, to obtain the water solution on one hand, and the fat solution on
the other. These two phases can then be used to make an emulsion (by whipping the liquid fat into the
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