Why Is Cheese Yellow When Milk Is White?

If a cheese has a natural buttery yellow color, beta carotene is responsible. Beta carotene is a fat-soluble yellow pigment and antioxidant found in grass. After a cow chews the cud, beta-carotene dissolves into the animal’s fat stores and ends up in fat globules in its milk. However, protein clusters and the membranes that surround fat globules in milk conceal the pigment’s color, reflecting light in a way that makes milk appear white and opaque. But during the cheesemaking process, the pigment is released: After bacterial culture and rennet have been added to milk and the coagulated mixture is cooked, the fat membranes dissolve and the protein clusters loosen so they can’t reflect light anymore. The beta carotene is made visible, and it also becomes more concentrated, since the the lean liquid component of the milk, called whey, is drained off. It follows that the fattiest cheeses, and those from cows grazed on open pasture, tend to have the deepest natural color.

More acidic cheeses, like cottage cheese and feta, retain their dense protein structures and so continue to appear white. Some cheeses made from other animals' milk, like goat cheese and buffalo mozzarella, are white because goats and water buffalo don't store beta carotene in their fat the way cows do. (Instead, they convert it to vitamin A, which is colorless.)

What about orange cheese? It’s been tinted with a yellow-orange vegetable dye called annatto, which is made from the seeds of the achiote tree. In 19th century, dyeing became standard operating procedure to address the problem of inconsistent cheese color due to seasonal variations. (Cheese made from spring and summer milk tended to be naturally yellower than cheese made from fall and winter milk, since grass is more abundant and nutritious in spring and summer.)

Today, many supermarket cheddars are still colored to satisfy consumer’s expectations of what cheese should look like. (Research has shown that color preferences influence how people shop for cheddar.) But inconsistent cheese color isn’t much of a problem anymore, since large-scale confinement farms have come to dominate dairy production over the last 30 years. Cows kept in confinement and fed a carefully formulated mix of grains, protein supplements, and dried grasses tend to turn out milk with virtually no irregularities. Milk from confined cows also contains considerably less beta carotene than milk from pastured cows—hence the need for dye.