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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

 

Still have more questions? You'll find more answers in our archived monthly feature articles by the Inquisitive Cooks.

(Meet the Inquisitive Cooks)

     
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.
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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