Homemade butter is pure physics

Milk is a wonderful, complex thing. It is basically an emulsion of proteins, lipids (fats), vitamins and some ions like calcium. And what is an emulsion? Well in short is a stable mixture of immiscible components, lets say like the water and the fat in the milk. We all know that water and fat don´t like mixing (just pour some olive oil in water), so what´s the trick here? The fat in the milk is dispersed in small globules that are stabilized by phospholipids. Phospholipids are bipolar compounds that have hydrophilic (likes water) and hydrophobic (hates water) parts. So they can form little pockets to stabilize the fat in the water of the milk, hence forming the nice white emulsion in your caffe latte.

So to make butter you have to separate the butter from the milk (or cream), meaning, you have to break the small pockets holding the fat globules and let them aggregate and separate from the water part of the milk.

For that we have to use a bit of force...
In this case I used a high fat cream. Cream is easier to use than milk for making butter, because the cream is already a step ahead in separation of fat from the milk. So choose something with at least 35% fat.

Then all you have to do is beat the cream like you would do for making whipping cream (but don´t add the sugar...). First you will see a nice whipped cream, then it will start curdling a bit and if you keep going you will see a separation of the fat aggregate and a white turbid solution.

This watery solution is buttermilk. Save it and use it to do, for example, a nice soda bread.
Now all you have to do is wash the butter with cold water (but discard this washing water), until the washing water comes out more or less clean.

You can also season the butter with salt, or even some herbs. In this example I used around 400 ml of 35% fresh cream, and in the end I got 200 ml of buttermilk and around 150 gr of butter. Half of it I just seasoned with a bit of salt, and the other half i added a mixture of herbs, pepper and salt.
With the buttermilk I am doing some nice muffins.... you´ll see them later.