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What's
really happening when you churn butter?
"
Dear
Anne and Sue,
Does churning butter just change
the emulsification process or are proteins being denatured?
Thanks
very much,
Colleen Fox and the Hazen High School AP Biology Class
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Making butter may sound easy, but as your question suggests,
it’s not quite as simple as it seems.
Changing whole milk to butter is a process of transforming
a fat-in-water emulsion (milk) to a water-in-fat emulsion
(butter). Whole milk is a dilute emulsion of tiny fat
globules surrounded by a lipoprotein membrane that keeps
the fat globules separate from one another.
Butter is made from cream that’s been separated from
whole milk and then cooled; fat droplets clump more easily
when they’re hard rather than soft. However, making
good butter also depends upon other factors, such as the
fat content of the cream and its acidity.
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Churning physically agitates the cream until it ruptures
the fragile membranes surrounding the milk fat. Once broken,
the fat droplets can join with each other and form clumps
of fat, or butter grains.
As churning continues, larger clusters of fat collect
until they begin to form a network with the air bubbles
that are generated by the churning; this traps the liquid
and produces a foam. As the fat clumps increase in size,
there are also fewer to enclose the air cells. So the
bubbles pop, run together, and the foam begins to leak.
This leakage is what we call buttermilk.
Thus, the cream separates into butter and buttermilk.
The buttermilk is drained off, and the remaining butter
is kneaded to form a network of fat crystals that becomes
the continuous phase, or dispersion medium, of a water-in-fat
emulsion. Working the butter also creates its desired
smoothness. Eventually the water droplets become so finely
dispersed in the fat that butter’s texture seems
dry.
All of us working on this site appreciate your kind comments!
Thanks for stimulating such interesting discussions in
your class. They sound like a fine group.
Cheers,
Anne & Sue
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