They say that butter makes everything better, and I tend to think that’s true. But riddle me this: Milk is white, and butter is made from milk, but butter is … yellow? If you explained this to an alien who knew nothing of Earth’s delicacies, they would likely expect tomatoes to turn pink when cooked into marinara or for cauliflower to turn purple while roasting. Neither of these makes sense, but honestly, the fact that butter is yellow doesn’t make a whole lot of sense either.
To get to the bottom of this mystery, I talked to food scientist Bryan Quoc Le, author of 150 Food Science Questions Answered. Read on to find out what he said, plus everything else you might want to know about butter’s qualities and quirks.
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Why is butter yellow?
The explanation is surprisingly straightforward, even if it’s not something that ever actually occurred to you: It’s all about the cow’s diet. “There are certain fat-soluble compounds known as carotenoids that are transferred from the grass the cow eats to the butter that is made from the milk,” explains Le. “It’s not a very high concentration, but it’s just enough to change the color to yellow.”
Also known as beta-carotene, carotenoids are the compounds that give foods like carrots and sweet potatoes their vibrant orange hue. Of course, grass isn’t orange, which means it doesn’t contain very many carotenoids—only enough to change the color of butter from white to yellow.
But wait, that brings us back to our initial question: Why is milk white and butter yellow? It comes down to fat content. Carotenoids are fat-soluble, which means they are essentially suspended in the fat in the milk. “The concentration of fat in milk is fairly low, about 3%, and that fat is evenly suspended throughout the milk. The result is that the amount of carotenoids in the milk isn’t sufficient to create the color,” Le explains. But when the milk is churned into butter, the fat becomes highly concentrated. “Butter is 80% to 85% fat, so the carotenoid concentration is about 28 times higher in butter than in milk. So there is a high enough level to cause a change in color and appearance.”
Why is U.S. butter paler than butter produced elsewhere?
If you’ve ever bought Kerrygold grass-fed Irish butter, you’ve likely noticed that the color is a much deeper yellow than butter made from milk from American cows. Why? Kerrygold cows exclusively eat grass, and most American cows do not. “Cows in the United States tend to be fed a diet of corn alongside forage (grass and hay),” says Le. He explains that corn is more energy-dense than grass, so this combination of feed options results in cows in the U.S. eating less grass, and therefore consuming fewer carotenoids, than cows that are eating grass alone.
Should you be concerned if your butter isn’t yellow?
Not necessarily, especially during the winter. “Cows are fed more grass during the spring and summer season, and butter from their milk tends to be more yellow as a result,” says Le. In general, the warmer it is outside, the more deeply yellow you can expect your butter to be.
Still, you may be concerned about white or cream-colored butter simply because it doesn’t quite taste the same as yellow butter. “Generally speaking, since the yellow color of the butter is a reflection of certain compounds that accumulate in the fat, it’s some level of indication that there’s going to be more depth in flavor,” Le explains. If you’re using butter for cooking or baking, you likely won’t notice the difference between white and yellow butter in your finished product. But if you’re spreading butter on a freshly baked scone or over a short stack of pancakes, you may be able to taste the difference.
Le adds that butter should only be white, cream or yellow. Any other colors present—such as gray or brown—would likely mean that the butter is spoiled or oxidized, especially if it has irregular spots or streaks on the surface.
Do manufacturers ever use yellow dye in their butter?
No, according to Le, though he says some do add annatto extract, a pigment derived from annatto seeds, to improve the yellow color of their butter. However, he notes that any added extract would need to be included in the ingredients list, so if you’re suspicious, you can look for it there.
While manufacturers generally don’t artificially enhance the color of butter, they have been dying margarine yellow to look more like butter since it came to the U.S. in the mid-1800s. And this caused a huge brouhaha. The fact that it looked and tasted so much like butter, plus was cheaper and lasted longer, actually caused states and eventually Congress to pass laws to slow down margarine’s rise in popularity. According to the folks who maintain Historic Sugartown, a preserved 19th-century village in Pennsylvania, there was a steep federal tax on yellow margarine, while some states even forced margarine to be dyed bright pink so it couldn’t be mistaken for butter. Congress finally repealed the tax on margarine in 1950, so (sadly? thankfully?) there’s no more pink margarine gracing tables.
What else enhances butter’s taste?
High-quality butter shouldn’t have much else added to it, so the makeup of the cow’s diet (mainly the ratio of grass to other types of feed such as corn, alfalfa and hay) is the biggest factor that influences quality, along with the cow’s metabolism and breed. Apart from the salt added to salted butter, manufacturers don’t mix any additional ingredients into butter. If you’re after a particular taste or texture, you can look for the words “cultured” or “European style” on the label, which will typically mean that the butter has a slight tang (cultured) or a higher fat content and thus a creamier texture (European style).
Additionally, “the length of time in which butter is exposed to oxygen during production and storage can have a serious impact on the taste of butter,” says Le. According to the Center for Dairy Research at the University of Wisconsin, packaging is the penultimate step in butter production, right before chilling. The larger the manufacturer and the bigger the batch of butter, the longer it may take for all of the finished butter to be packaged, and the longer it may spend in storage before making its way to you, the consumer. “Any butter that has spent more time in storage will eventually lose many of the flavor compounds that give it its richness,” says Le. “It is going to taste bland, metallic or even have hints of rancidity.”
Smaller batches of butter from smaller producers, on the other hand, do not spend as much time in storage and therefore may maintain a richer taste. “Probably most customers will not notice, but depending on the genetics of the person or their childhood exposure to certain higher-quality butters, others may be able to detect a difference,” says Le.
Likewise, once you’ve brought your butter home, repeatedly unwrapping and rewrapping it exposes it to oxygen. If it takes you a while to go through a stick, the final few tablespoons may be a little less flavorful than the first for this reason. (Storing butter in the back of the fridge instead of the door can also help with this.) But honestly, I don’t know anyone who takes long enough to notice.
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Sources:
- Bryan Quoc Le, PhD, food scientist and author of 150 Food Science Questions Answered; email interview, June 2026
- Fresno State Animal Sciences and Agricultural Education: “Manuel Mancebo Jr. and Katye Mancebo Dairy Production Unit”
- Historic Sugartown: “The Color of Butter (and the Great American Butter Wars)”
- U.S. Dairy Forage Research Center: “What Do Dairy Cows Eat?”
- Center for Dairy Research: “Butter Science 101”
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