mold on butter
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Mold on Butter – What’s the Cause and What to Do

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Soft, rich, and utterly indulgent, butter is a staple food for many families! There is nothing quite like the taste of real butter, whether you use it for baking or for smearing generously on golden slices of toast.

But if you find mold on butter, what should you do?

The main causes of mold on butter are contamination, heat, and exposure to air. Butter that has gone moldy should not be eaten, as it may contain harmful toxins. The best way to keep butter fresh and free from mold is to keep it chilled in an airtight container.

Want to keep your butter fresh and delicious? We’ve got all the answers and more for you! We will take a look at what to do with moldy butter and give you some tips on the best way to store this dairy indulgence.

What Is Butter?

Rich, smooth, and flavorful – there aren’t many people who don’t enjoy the depth of flavor which butter adds to your diet!

Butter is a dairy product that has many uses and is popular as a baking ingredient. It is almost always used in sandwiches and on toast, adding a rich flavor to sauces and pan-fries.

But what exactly is butter? If you have never had a go at making butter yourself, you might wonder what miracles happen to create this delicious block of dairy goodness.

The basic ingredient for butter is the creamy part of milk. Butter is normally made using the cream from cow’s milk, but in some countries, the milk from sheep, goats, buffalo, and even yaks can be used to make butter.

How Is Butter Made?

When you look at a carton of cream in your refrigerator, it can be hard to envision how this could be turned into butter. But this is where the magic happens … emulsification!

Emulsification is the process of suspending fat in water, turning two ingredients that do not normally mix into a smooth blend. In butter, the milk proteins act as the emulsifier, blending the butterfat in the cream with the liquid portion.

This is done by a process called churning – traditionally this was done by hand, but modern-day methods use machines. Churning means that the cream is mixed vigorously, causing the fat globules to rupture and join together. These form clumps of fat, with liquid trapped inside them. 

Eventually, you will end up with smooth lumps of butter, floating in a thin milky liquid. This liquid is called buttermilk and is a useful by-product of butter. The buttermilk is drained off and the solids are shaped into a firm pat of butter.

Storing Butter

Butter is quite unusual, as unlike other dairy products, its texture changes according to the temperature.


When chilled, butter is a solid, and when heated it becomes a liquid. At room temperature, butter is semi-solid – the perfect state to spread on our toast!

With dairy products, we are all accustomed to being extra cautious when it comes to storage. Most milk-based products need to be kept cool at all times, otherwise, they deteriorate very quickly. So why is butter so different?

It all comes down to the high fat and low water content of butter. This inhibits the growth of mold, even at room temperature. However, butter can still go moldy under the right conditions.

What Causes Mold on Butter?

Butter is a relatively stable dairy product and normally has a long shelf life. Unlike other milk-based items, such as yogurt, butter does not go moldy easily.

In fact, it can be stored in the refrigerator for up to three months, even after it has been opened! However, butter can go moldy, and there are a few reasons why this may happen.

1. Contamination

The main culprit in many households is the use of contaminated utensils. And yes, we all know how that happens, and many of us are guilty of it ourselves!

When you’re making a batch of sandwiches for the family, sometimes it just seems easier to use the same knife for everything. So, you butter one round of bread, spread on the peanut butter or jam, then move on to buttering the next round of bread.

And now your butter is contaminated with tiny particles of whatever you have filled your sandwiches with – oops!

Even if you wipe your knife clean when you switch between sandwich fillings, contamination will still occur. And even if you are just buttering bread or toast, crumbs are inevitably going to end up in your butter!

2. Heat

Exposure to heat greatly increases the likelihood of your butter going moldy. The first reason for this is that heat will promote the growth of mold, allowing it to spread and grow more quickly.

Secondly, when butter is warm, it becomes softer. This allows the mold to penetrate deeper into the butter itself.

3. Air

For mold particles to contaminate your butter, they will normally travel through the air. Butter which is not kept in an airtight container is much more likely to become moldy.

Air also causes another problem – oxidation. This is a natural process where food deteriorates when exposed to air. This causes your butter to become rancid and unpalatable.

4. Salt

In the grocery store, you will see two types of butter – salted and unsalted. Salt is an excellent preservative and will inhibit the growth of mold on butter.

Unsalted butter is much more likely to go moldy, particularly if stored at room temperature.

How Do You Know if Butter Has Gone Bad?

To check if your butter is safe to eat, you will need to carry out a close inspection of the following areas:

1. Appearance

Look at the surface of the butter – can you see any fine hairs of mold developing? Widespread mold will be more obvious, creating a furry appearance to the butter.

Check the color of the butter too. Look for discoloration – fresh butter should be an even, light yellow color. Any changes may mean your butter has gone rancid.

2. Smell

Give your butter a good sniff – does it smell sweet and milky? Milk that has gone moldy will have a distinctive musty smell. Rancid butter will smell sour and unpleasant.

3. Taste

Only taste your butter if it has passed the appearance and smell tests! Moldy and rancid butter will be extremely unpalatable, with a sour and tart flavor.

Is It Safe to Eat Moldy Butter?

Unfortunately, if you see mold on your butter, it is no longer considered safe to eat.

The US Food and Drug Administration (FDA) has classified butter that is moldy as unsafe to eat. Not only do you risk food poisoning and botulism, but the toxins will damage your immune system.

This is a particular concern with butter which is soft, especially that which is stored at room temperature. The softer consistency allows mold to penetrate deeper into the butter, spreading toxins along the way.

Slightly Moldy Butter – Can I Cut It off and Eat the Rest?

So, you’ve opened your butter dish and there is a thin layer of mold on one area. How disappointing, especially if you’ve got a busy day of cooking planned! But can you cut the mold off and eat the rest?

Official advice from the FDA is that any butter which has mold present should be discarded, as it presents a threat to human health.

mold on butter

However, many people will tell you that they would just cut off the moldy section and eat the rest anyway – so is this safe to do?

Obviously, we strongly advise that you stick with the FDA guidance – these guys definitely know what they are talking about when it comes to food safety!

But if you’re tempted to try and rescue your moldy butter, we want to make sure you go about this in the safest possible way.

Things to consider if cutting the mold from butter:

  • Never do this on butter that has been left out at room temperature. The warmer temperatures will have softened the butter and allowed mold and toxins to penetrate deeper than you would expect. Only ever trim mold from butter that has been kept chilled or frozen.
  • Remove your butter from its packaging or container before attempting to trim the mold. The existing packaging should be discarded, and any containers used should be washed thoroughly.
  • Be generous when you trim your butter! You need to leave a large margin between the mold and the part you are going to consume.
  • Use a clean, sharp knife and clean work surface.
  • When you have finished cleaning the mold from your butter, transfer it to a clean, airtight container and store it in the refrigerator.
  • Use the butter as soon as possible – it is unlikely that you will have removed all of the mold spores, and it will quickly spread through the remaining butter!

Should I Be Concerned if I Accidentally Ate Moldy Butter?

If you accidentally ate some moldy butter, don’t panic! It is very unlikely that moldy butter would cause food poisoning, especially as butter is normally eaten in very small amounts.

However, there are risks with eating moldy butter, which is why the FDA advises against it. Molds release toxic substances, known as mycotoxins. These can cause allergic reactions and respiratory problems.

Moldy butter is also very likely to be rancid – this means that it has fully gone bad. As well as tasting disgusting, rancid butter will spoil any recipe if you try and cook with it.

Can I Bake With Moldy Butter?

Baking with moldy butter is equally as hazardous as eating it in its raw state. This is because the baking process will kill the molds on the butter, but it will not remove the mycotoxins.

Tasty butter on wooden cutting board

These toxic substances will remain in your butter, even if it is heated through or baked.

How to Prevent Mold on Butter

To understand how to prevent mold on butter, we need to look at the causes of mold again.

1. Contamination

Avoid contaminating your butter with other foodstuffs, as this is the main cause of moldy butter. Use a separate butter knife, and make sure it is cleaned regularly. Any crumbs or contamination of your butter should be carefully removed.

2. Heat

Butter which is kept chilled is much less likely to go moldy. Keeping your butter in the refrigerator is the obvious solution, but this can make your butter hard and difficult to spread.

If you prefer to keep your butter at room temperature, avoid direct sunlight and warmer areas of the kitchen.

3. Air

Butter should be kept in an airtight container at all times. If you use a butter dish, make sure it has a tight seal around the edges. Butter often comes wrapped in paper, which is not suitable for long-term storage.

4. Salt

Salted butter is much less likely to go moldy, especially if you want to keep it at room temperature. Most people keep salted butter at room temperature for sandwiches, and unsalted butter in the refrigerator for baking.

Related Questions

Can Butter Be Frozen?

Freezing butter is a great way to prolong the shelf life of this versatile dairy product.

When frozen and defrosted, there is very little change to the flavor and texture of butter. And if you didn’t already know this great cooking tip, frozen butter makes perfect pastry dough when it is grated into flour!

Butter should be protected from the air when frozen; the best way to do this is to keep it in its original packaging, wrapped in an extra layer of foil or freezer wrap.

You can also chop your butter into smaller portions and freeze it in an airtight container.

Salted butter can be kept for up to nine months in the freezer. Unsalted butter will keep for up to five months in the freezer.

What Is the Best Way to Soften Hard Butter for Sandwiches?

We all know that horrible feeling when you’re rushing to make sandwiches in the morning and realize you’ve forgotten to take the butter out of the fridge the night before!

But rather than tearing your bread to pieces with solid butter, there are some quick and easy ways to soften butter.

The best method to soften butter for sandwiches is to cut off the amount of butter you require from the main block of butter.

Cut this into smaller chunks, then mash with a fork. Leave your mashed butter in a warm place for 5-10 minutes and it should be much more spreadable.

Alternatively, if you are in a hurry, the microwave can be used to soften butter. Take care with this method, as the microwave will quickly turn even the hardest butter to liquid!

We’d suggest using a low-medium setting at bursts of 10 seconds at a time until your butter is the desired consistency.

How Do You Store Butter at Room Temperature?

Many of us keep our butter at room temperature at all times, with no adverse effects. However, this is most likely because we get through a block of butter very quickly!

Food authorities advise that you should only store the amount of butter you will eat within one or two days at room temperature. The remainder should be stored in the refrigerator.

The best way to store butter at room temperature is in a dark-lidded container, which does not allow light or air to access the butter. Keep this container in an area with a consistent ambient temperature, away from heat and direct sunlight.

Up Next: Is Butter A Condiment?

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