cultured (left) vs uncultured (right) butter

Why Different Butters Behave Differently – Butter Science

If you’ve ever switched butter brands, you might have noticed that one butter isn’t necessarily the same as another. Your new butter might have a paler color, be harder, or differ in flavor from what you’re used to. Sometimes, the differences are obvious. Other times, they’re more nuanced.

Since butter is a natural product, made from the milk of cows, these differences are perfectly normal. Even butter from the same brand, bought at a different time of the year can be slightly different. This is due to the changes in the composition of the milk it’s made from, but may also be due to decisions made by a butter manufacturer. To understand the differences, we’ll need to start at the beginning: the cow.

Butter is made from just milk

Butter starts out with a cow, grazing in a (grass) field, or a barn. Once a cow has given birth to calves, she can give milk. Cow’s milk contains about 4% milk fat, though the exact amount varies. The fatty phase of milk is called the cream. If you leave unhomogenized milk to sit for some time, that creamy layer will float to the top. In factories, this layer is separated from the rest by using large specialized centrifuges. This cream, which contains 30-40% fat, can be converted into butter through a process called ‘churning’.

Fat has a lower density than water, which is why it floats to the top, or can be separated using a centrifuge. The science behind it is the same as the science explaining why chocolate milk splits over time. It is also used to make clotted cream.

Churn cream into butter

During churning, you agitate cream in order to induce the individual fat droplets to clump together. These clumps of fat still contain some water. But, by now it’s made up of at least 80% fat + 20% water, we’ve made butter. As you may notice, so far all we’ve used is milk, nothing else, to make butter. You may need some salt for salted butter, but that’s it. Making butter is, at its core, a simple process. Nevertheless, there are ample ways in which butters can turn out a little different.

an infographic explaning the science behind butter

Milk fat type impacts hardness

Since milk fat makes up most of a slab of butter, it has a huge impact on the final properties of the butter. Once of the most well researched effects is the effect on hardness. Some butters seem to remain hard, even when taken out of the fridge well in advance, whereas other butters soften quite quickly after taking them from the fridge. This difference in hardness is caused by the composition of the fat.

Milk fat is a mixture of fats

Since butter is made from just one ingredient, milk, the composition of the milk determines the composition of the final butter. Milk fat isn’t just made of one type of fat. Instead, it’s a mixture of different fats. These fats are called triglycerides, which each contain 3 fatty acids. The types of fatty acids present in a triglyceride determine its behavior. Even though, generally speaking, the ratio of fatty acids in milk remains quite similar, differences of a few percent up and down are not uncommon. And all of these differences, start out in the cow.

most prevalent fatty acids in butter
Some of the most common fatty acids found in butter, and thus milk fat. Note that the given percentages are just indicators, they can differ by a few percent, depending on the milk the butter is made from.

Cow’s life determines fatty acid composition

Cows are animals. Not standardized machines. As a result, they won’t always produce the exact same milk. The fat, protein, and mineral content and composition can all vary. Modern-day manufacturing processes are good at standardizing the overall content of fat in milk. But, they can’t correct for a difference in the type of fats in the milk. As such, you’ll continue to find these differences. The differences can be due to a range of factors, of which we’ll examine a few below.

Feed of the cow

The food that a cow gets to eat can have a tremendous impact on the types of fatty acids present in their milk. A cow that has only (or mostly) eaten grass will produce milk (and butter) with a different composition than a cow that was mostly fed on grain, or grass with plenty of clover. This has been shown to impact hardness, color, even the flavor butter made from the milk!

Lactation cycle of the cow

First, cows give milk because they’ve given birth to a calf. In the months that follow calving the volume as well as the composition of the milk will change. Most of these changes can be standardized in a factory, but not all.

calf looking at you
The cow’s DNA

To some extent, the composition of milk is hereditary. That is, different breeds of cows make milk with their ‘own’ composition. But, even within a breed differences may occur as well. The differences within a breed tend to be less noticeable, and when all blended together, can be evened out and corrected for.

Geography & seasonality

The location where the cow lives as well as the season you’re milking the cow impacts the cow’s milk composition. There is a lot of interaction here with the feed though, since most cows have a different diet during winter than during summer for instance.

Fatty acid composition impacts hardness

Every fatty acid has a different melting point, that is, the temperature at which it transforms from a solid into a liquid. If that melting point is above room temperature, the fatty acid will still be solid at room temperature. If the melting point is lower than room temperautre, it will be liquid. Since every fatty acid, and even combination of fatty acids, has its own melting point, butter as a whole doesn’t just melt at one temperature. Instead, it softens and melts over a range of temperatures. The more fats are molten at a specific temperature, the softer the butter becomes.

If the fatty acid composition of your milk changes, the hardness of the butter changes. This can cause one slab of butter to be harder than another one. Since the composition is fixed once the cow has been milked, there’s not much factories can do here, except for trying to change a cow’s diet over time.

Over time, butter hardens

You may also perceive differences between different butters simply because some are ‘younger’ than others. The effect shouldn’t be as pronounced as the effect of fatty acid type, but, researchers have shown that older butter tends to be harder. Over time, even some fats that solidify very slowly will turn solid.

β-carotene impacts color

The color of butter is greatly influenced by the amount of β-carotene present in the milk. Even though β-carotene only makes up a very small portion of the milk! This pigment, which also makes a carrot orange, gives a slight yellow color to butter. Again, the amount of β-carotene is heavily influenced by a cow’s diet. Cows that each grass for instance tend to have more β-carotene in their milk than cows that eat grains.

Some butters contains colorants

That said, some butter manufacturers may simply add color to the butter, adding to its color. In those cases, the cow had nothing to do with the color of the butter.

Cow’s diet impacts flavor

Lastly, you may notice differences in flavor between different butters. Flavor is probably the most complicated topic since it depends on a range of different molecules and effects. Aside from fats and flavor molecules, even proteins present in the butter can play a role. However, it has been shown that, yet again, the diet of a cow can influence the flavor of butter. So if your cow has been inside all winter, the flavor of the milk and thus butter, can be different than when you’re cow has been grazing outside during summer. This is not something manufacturers can easily correct for.

How you use and process butter can have a tremendous impact on the flavor of butter as well. Heating butter to make brown butter for instance initiates a range of chemical reactions that change the flavor of butter!

The impact of processing

Even though the living conditions of cows clearly have a huge impact on your butter, that’s not all. How that milk is made into butter can also impact the properties of your butter. Some noteworthy steps to mention are culturing and salting the butter.

Cultured vs uncultured butter

You can make butter from milk rather quickly by centrifuging and then churning the butter. However, some manufacturers add an additional step: culturing the milk. Historically speaking this happened ‘automatically’. As you waited for the cream to separate from the milk, microorganisms may start to grow in the milk. Nowadays, manufacturersa add cultures of microorganisms. These microorganisms grow and thrive and in the process release a range of flavors and possibly even color molecules. As such, this additioanl process can impact color, flavor, but also hardness of the butter.

cultured (left) vs uncultured (right) butter

Salted vs unsalted butter

You’ll notice this difference immediately when tasting: whether a butter has been salted or not. It’s also one of the few differences that you can easily find stated on the label. Salt adds flavor and it helps to extend the shelf life of butter.

Which butter is best?

Well, it depends! There is no one best butter. For one thing, the availability of butter varies greatly between countries and regions. Also, it depends on what you’re using it for. Here’s a few suggestions on what to look out for!

  • Are you eating bread or toast with a little butter, then you’d want to go for the most flavorful butter you can find. You might also want to consider salted butters.
  • In most baking applications you’d want to use unsalted butter, this will give you optimal control over the amount of salt that you add.
  • Making croissants, or other types of laminated pastry? Then you’d generally prefer a butter with a slightly higher fat content, and also one that is a little harder, to prevent melting. For instance, we found our local grass-fed butter worked less well than ‘regular’ butter. The grass-fed simply melted away too quickly. The same can be true for products such as pie crusts.
  • Does butter make up just a small fraction of your recipe? Chances are, any butter will work fine. Even exchanging it for a (plant-based) margarine might not give you any problems.


Alothman M, Hogan SA, Hennessy D, Dillon P, Kilcawley KN, O’Donovan M, Tobin J, Fenelon MA, O’Callaghan TF. The “Grass-Fed” Milk Story: Understanding the Impact of Pasture Feeding on the Composition and Quality of Bovine Milk. Foods. 2019 Aug 17;8(8):350. doi: 10.3390/foods8080350. PMID: 31426489; PMCID: PMC6723057.

Cheese Science Toolkit, Stage of lactation, link

Dairy processing handbook, Centrifugal separators and milk standardization, chapter 6.2, link; a great in-depth explanation of how a centrifuge works for separating cream from milk

Dunn, E.G., Irish Butter Kerrygold Has Conquered America’s Kitchens, Oct-2, 2019, Bloomberg business week, link

Marangoni, Alejandro & Mirzaee Ghazani, Saeed. (2021). Perspective: A commentary on elevated palmitic acid levels in Canadian butter and their relationship to butter hardness. Journal of Dairy Science. 104. 9380-9382. 10.3168/jds.2021-20469.

O’Callaghan TF, Faulkner H, McAuliffe S, O’Sullivan MG, Hennessy D, Dillon P, Kilcawley KN, Stanton C, Ross RP. Quality characteristics, chemical composition, and sensory properties of butter from cows on pasture versus indoor feeding systems. J Dairy Sci. 2016 Dec;99(12):9441-9460. doi: 10.3168/jds.2016-11271. Epub 2016 Oct 19. Erratum in: J Dairy Sci. 2018 Sep;101(9):8616. PMID: 27771086.

O’Callaghan, T., Hennessy, D., Impact of cow feeding system on the composition and quality of milk and dairy products, Teagasc, Grass-fed dairy conference, 2018, link

The cattle site, Managing Cow Lactation Cycles, May-18, 2015, link

Wageningen University, Milk Genomics Initiative: Cow’s DNA determines composition of milk, link


  1. There’s something more going on here, it’s not the harder butter that bothers me, it’s what it does to my stomach given me a bloated feeling.

    • Hi Robert,

      I’m not familiar with all types of butter, but had a quick look online on the Walmart website. Their ‘Great Value’ unsalted butter contains 80% fat (8g per 10g portion) so that’s similar to other butters. Generally speaking, in order to call something ‘butter’ it needs to contain around 80% fat, though exact regulations differ per country.

      Keep in mind that as soon as it’s no longer called butter, but if the name contains terms such as ‘buttery’ or ‘spread’ it’s probably no longer butter and those product will contain a lot less milk fat. They may contain other fats such as vegetable fats. The label will always give the amount of fat that’s in the product, so that’s a way to verify.

      Hope that helps!

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