If you’ve ever wondered about butter’s sunny hue, you’re not alone. A reader wrote into the New York Times’s “Ask Well” column to ask what makes butter yellow, when butter is made from milk, which is white. An important question, given that color is a key consideration for the most discerning butter consumers. As it turns out, the yellow color of butter is directly linked to its fat content. Sophie Egan explains that cows eat grass and flowers, and yellow beta-carotene from those plants is stored in the cows’ fat. The pigment is carried with the fat into the milk. But, because milk is mostly water and contains just 3 percent fat, the yellow color doesn’t come through. Butter, on the other hand, contains at least 80 percent fat.
You may now find yourself wondering why cream, which contains between 30 and 40 percent fat, has the same white color as milk. (Or maybe you had forgotten that cream does indeed contain ten times as much fat as whole milk. Welp.) There’s a scientific reason for that, too. When suspended in milk or cream, a membrane surrounds the beta-carotene-containing fat globules, essentially obscuring the yellow color. When milk or cream is churned, as is required when making butter, the membrane is broken and beta-carotene is released, turning the butter solid yellow.
Interestingly, other animals don’t store beta-carotene in the same way that cows do, so butter made from sheep’s milk or goat’s milk is white. If you’ve noticed that even your grocery store butter is whiter than the picture of butter you have in your head, it’s because those cows, products of the industrial dairy system, never grazed on green pastures. Yellow butter not only looks best against the golden brown of a flapjack but, in some cases, comes from happier cows. However, knowing that color affects how we perceive taste, some dairy producers add in the yellow using annatto, a food-coloring agent derived from the seeds of the achiote tree. Just one more thing to think about when mulling over your many butter options.