The Science of Butter

Learn why butter is yellow while exploring the process of making cultured butter from cow to consumer.

| January 2020

For a product made predominantly from one ingredient (cream), butter has a surprisingly interesting story. To really understand it, it’s helpful to delve into the physics – or at least touch on it – as well as run through the process of making butter.


First there’s the milk, ideally from a well-bred Jersey cow. I use Jersey and Guernsey herd milk, due to the breeds’ ability to produce an extremely high-fat and beta-carotene-rich milk. Beta carotene is naturally present in grass and it is what gives milk its fat-rich yellow pigment. The more grass a cow eats, the yellower the milk will appear – that’s why summer cheeses and butters are much more colorful than those made in winter. For me, butter should be yellow, so choosing a cow’s milk that has the capacity to produce a beautiful yellow butter has always been a priority.

Milk is a liquid with butterfat naturally emulsified within in it. The fat cells have a lower density to water, which is why we see cream rise to the top of a milk bottle – at least the unhomogenised milk the milkman used to deliver in glass bottles. (A favorite childhood story from my mum is the race between her and her brother to the front door to see who could get the cream from the milk on to their cornflakes.)

Separating the cream from the rest of the milk is the next part of the process. Historically (before industrialization), fresh milk would be left out in a large vat. After a day or two the cream will have naturally risen to the top of the vat and would then be skimmed (ladled) off from the top, leaving ‘skimmed’ milk left over.

Once centrifuges (a machine that spins at such a velocity that the cream rises higher than the milk) were introduced, the traditional techniques became obsolete.



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