Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
Why is butter yellow?
Some milk contains a lot of carotenoid pigments in the butterfat. When the butterfat is skimmed off and churned into butter, the butter is yellow.
You make homemade butter by shaking a jar full of heavy whipping cream (or overwhipping your cream), but it is seldom as dark a yellow color as the butter you buy in the store. This is because commercial butter often has carotenoid pigments added to make it look richer or to match the buyer’s idea of what butter should look like.
You can extract your own carotenoid pigments to color your own homemade butter if you like. First, grate some carrots. Then melt some butter in a pan, and gently sauté the carrots in the butter. The melted butter will extract some of the carotenoid pigments from the carrots. The oily liquid that floats to the top is clarified butter, which is quite a bit darker than it used to be.
Cool the clarified butter. Now you can use a mixer to blend it into the homemade butter to get a deep yellow color.