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. Duplicitous English farmers first began dyeing cheeses
in the 16th century (originally using marigold petals or carrot juice)
because the dye made low-fat cheese look more like high-fat cheese,
which commanded higher prices. When U.S. commercial
cheese production took off in the second half of the 19th century,
dyeing with annatto 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.


Thanks to Mark E. Johnson of the Center for Diary Research at the
University of Wisconsin.