Mold On Butter: Is It Safe To Use Moldy Butter & Can It Be Saved?

So, what do you do if you’re making a batch of croissants, only to find patches of mold growing on your butter? Can you still cook with it? Are the fungi dangerous, and how can you prevent this from happening again?

Butter with mold growing on it should not be consumed as harmful bacteria and fungal mycotoxins can be present and cause health complaints such as food poisoning. Scraping mold off would still not make it safe to eat, as microscopic fungal growth could be present deeper within the butter.

In this article, we address all these questions and then some, so for everything you could ever want to know about mold on butter, keep reading.

Can you eat butter with mold?

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Is it safe to use moldy butter?

It is never advisable to eat butter that you have found mold growing on. By the time you notice patches of growth, the fungi are already well established and have likely spread through much of the butter. Mold growth is also common in food items that have begun to spoil, so not only could eating the butter cause you to ingest mycotoxins but there is a very high chance of consuming large enough amounts of bacteria to cause food poisoningOpens in a new tab..

Aside from the potential health risks, eating moldy butter would be highly unpleasant, as the bacteria that are almost certainly present will have begun to break down the proteins and fats, causing them to take on a sour smell and putrid taste.

Should you find mold growing on any part of the butter you have purchased, including the lid or container, you should throw it away and not risk ingesting any of it.

What happens if you accidentally eat moldy butter?

The good news is that if you were to eat a very small amount of mold as a result of it growing on your butter, in most cases there would be nothing to worry about, as many people would present no symptoms.

Symptoms occur more commonly in people who are particularly sensitive to the spores, such as asthmatics and people with suppressed immune systems.

If you discover that you have eaten moldy butter and then begin to suffer from new symptoms such as shortness of breath, nausea, or gastrointestinal discomfort, you should seek medical assistanceOpens in a new tab.. If you don’t notice anything immediately, monitor yourself over the next few days for any new symptoms.

What types of mold grow on butter?

The most common strains of fungus found growing on butter are AlternariaOpens in a new tab., CladosporiumOpens in a new tab., and Penicillium RoquefortiOpens in a new tab. (the strain that gives Roquefort cheese its characteristic taste, smell, and texture.

Alternaria strains typically present with a dark and smokey appearance, with a wooly texture.

Cladosporium strains have a greenish to brown or even gray hue with a powdery or velvet-like texture.

Finally, Penicillium Roqueforti has a dark green texture, sometimes with a slight blue twinge, and again has a velvet-like or powdery texture.

While these are some of the more commonly seen strains, this list is not exhaustive, and other strains can be found, some of which include:

Are the molds dangerous?

The Alternaria, Cladosporium, and Penicillium roqueforti mold strains all can cause health problems and in some cases, even medical emergencies if ingested, inhaled, or if physical contact is made with them.

Fungi can produce mycotoxinsOpens in a new tab. when they feel threatened which can cause allergic reactions and symptoms in people with suppressed immune systems, allergic asthma, and even otherwise healthy individuals in some

Inhalation, ingestion, or physical contact with mold can cause the following symptomsOpens in a new tab.:

  • Nausea
  • Breathing problems
  • Skin irritation
  • Watery eyes
  • Runny nose
  • Gastrointestinal discomfort
  • Vomiting

It is, therefore, always best to be cautious when dealing with fungi you’ve found growing on any type of food.

What does moldy butter look like?

Fresh butter has a light yellow color, and as it begins to become rancid and mold on butter develops, you may notice green, blue, white, or dark spots and patches appearing on the surface, as well as a general discoloration and change in the texture of the butter itself. After several days it may begin to curdle, which is where the fats and water separate, creating a lumpy texture, it may also feel gritty. As soon as you see or feel this, you should throw the butter away, as it is way past its best and cannot be saved.

If you’d like to see a great demonstration of exactly what mold looks like while it’s growing on a stick of butter, take a look at this time-lapse below.

Why does butter grow mold?

Dairy butter has the potential to grow fungi just as any other organic product or material can.

Despite having lower water content than other dairy products such as milk and yogurt, butter still provides enough moisture as well as small amounts of protein that fungi can use for both hydration and nutrition.

The higher salt content of salted butter increases its shelf-life when compared to unsalted, however, with enough time and under the correct circumstances, mold will still grow on salted butter.

Once the use-by date listed on the packaging the butter came in has passed, the rate at which butter will become rancid will speed up. It is once expired butter has become rancid that fungal growth is more likely to begin to develop.

Despite having its milk solids removed, types of clarified butter (such as ghee), can still develop fungal growth, however the process will take considerably longer. This is also the case with low-fat butter substitutes such as margarine, as any fats present will oxidize quickly, and will not only make the spread taste foul but will become an excellent environment for fungi.

What causes butter to become moldy?

There are five main causes of butter becoming moldy, these are:

  • Humidity
  • Cross-contamination
  • Salt content
  • Temperature
  • Exposure

Now that we know the major causes of its growth, let’s dive into them a little further.


Butter has a relatively low water content which causes fungi to grow at a slower rate than other dairy products. This is what allows it to be kept out at room temperature for several hours, whilst other dairy products would be spoiled much more quickly.

The butter itself may have a low water content, but if the product is stored in a high-humidity area (greater than 60%Opens in a new tab.), the airborne moisture can condense on the butter and provide mold with all the moisture it needs.


As its name would suggest, cross-contamination can occur from multiple sources, from bacteria and fungal spores being present during the bottling process, to transport and even from within your refrigerator.

If airborne fungi spores find their way onto your pat of butter from any other source, they can quickly begin to spread.

For example, if you had a pack of raspberries in your fridge that had begun to mold, all it would take is for the door to be opened, a gust of wind to blow the spores from the raspberries to other parts of the fridge, and over other food items, including your (previously) fungi-free butter.

Salt content

Whilst regular butter does have some naturally occurring salt (11mg per 100g), salted butter has roughly 643 (mg) of salt per 100g. This increased level of salt helps to draw moisture out of the butter.

As stated above, mold needs moisture to survive, so drawing liquid out of butter makes it less of a hospitable environment.

Salted butter does fend off fungi and bacteria growth for longer than unsalted butter, but it does still have a shelf-life, and will only stop mold growth from occurring for 30 days (1 month) longer than unsalted.


The ideal temperature to store butter is 41° Fahrenheit or lowerOpens in a new tab.. At this temperature, fungi cannot spread as quickly as they would at even a slightly higher temperature.

For example, the ideal temperature at which mold can grow most efficiently is between 60-80° FahrenheitOpens in a new tab., so you can see how easily a slip-up on the thermostat or a door being left open by accident can allow mold to grow at its most rapid rate.

Many people like to store butter outside of the fridge to make it easier to spread, this is fine, however as the butter will be at room temperature, it will be right within the temperatures outlined above, and fungi will quickly begin to grow after only a few days. It is for this reason that butter left out of the fridge should be consumed within two days.


If left uncovered in the fridge or (even worse), out on a countertop and left at room temperature, fungal spores can very easily land on the butter and begin to start a new colony. This is mitigated somewhat by using a butter dish (also called a butter crock), as it is exposed to fewer airborne spores, however, once it is opened, spores will be able to settle and create a colony.

It is also linked to the point about cross-contamination we discussed earlier, as butter that is kept within its wrapper, or (even better), an airtight box will not only decrease the available oxygen but also help to prevent cross-contamination from other potential sources of mold within your fridge or property.

How long does it take for mold to grow on butter?

Fungi can grow surprisingly quickly under the correct circumstances. If left out at room temperature for more than a few hoursOpens in a new tab., unsalted butter can begin to form mold, with visible mold patches becoming present within only a few days.

Salted butter will take a little longer to become moldy, even when left at room temperature, it will take several days before fungi will begin to grow.

When refrigerated, salted and unsalted butter will last considerably longer and grow mold much more slowly.

How to prevent mold from growing on butter

The good news is that there are several ways to lengthen the shelf-life of butter and prevent fungal growth, which are:

Restrict airflow

Keeping your butter in an airtight plastic or glass container will help prevent airborne fungi spores from landing on the butter and starting a colony. It may also help to maintain a more consistent temperature for short periods, such as when the fridge door has been opened and closed.

Keep it in the bottom and towards the back of the fridge

The bottom of the fridge is the area with the most consistent temperature, due to warmer air rising to the top. The back of the fridge also tends to benefit from more regular temperatures when compared to the shelves in the fridge doors where butter is often stored.

Keep it dry

Moisture is one of the main contributors to fungal growth, so keeping your butter dry will increase its shelf life and help slow mold growth.

Storing the butter in the bottom of the fridge will not only help to regulate its temperature but also keep it in one of the lowest humidity areas.

When storing the butter outside of a refrigerator, it is best to keep it in a dry location, away from direct sources of moisture such as cookers, kettles, and microwaves.

Avoid cross-contamination

Cross-contamination can be prevented by making sure you use clean cutlery to cut and spread butter and put the butter back into its container as soon as possible to prevent mold spores from other locations from finding their way onto it.

Opt for salted if mold is a concern

If you’re finding fungi growth to be a consistent problem and are currently using unsalted butter, then using salted butterOpens in a new tab. will solve the problem part of the way at least.

Switching to salted butter will add a few extra days to the shelf-life of your butter, but other methods described above should also be utilized to maximize the amount of time your butter stays fresh.

*One quick note here is that if you have any condition where salt intake needs to be closely monitored and kept low, continue to use unsalted butter but follow the other steps provided in this article.

Can moldy butter be saved?

Unfortunately, moldy butter cannot be saved, once it has begun to grow fungi it should be discarded. Whilst you may read that you can simply cut the moldy parts of the butter off and use the rest, this is heavily advised against.

The reason you should not use butter that has mold on it is that some strains of mold can produce aflatoxinsOpens in a new tab. a harmful and potentially cancer-causing toxin that can be present and completely unnoticeable within the butter.

Without knowing exactly which type you have discovered, it would be very difficult to know if you were dealing with aflatoxins or mycotoxins, either way, it’s simply better to discard the butter than to try and save it.

There is also the bacterial factor to consider, which would make the butter taste and smell foul, so there would be no benefit to removing mold and trying to consume the rest.

Can butter mold in the fridge?

Butter can become moldy in the fridge, but this occurs much more slowly than it would at room temperature.

Fungi do not die when it is subjected to cold temperatures, they simply slow down their growth rate, and if cold enough, go into a state of hibernation until the temperature rises again. There are even some strains that can happily grow at 32° FahrenheitOpens in a new tab. (0° Celcius).

So, putting butter in your fridge will certainly slow the rate of both mold and bacteria growth, but will not stop it entirely.

If you are very concerned about your butter becoming moldy despite being refrigerated and want it to last even longer, then freezing it may be a good option.

Butter can be frozen for up to four months before it may begin to lose its flavor and texture, but fungi and bacteria growth will have been brought to a near complete stop by doing so. Once the butter has thawed it can be used for an additional 30 days.

Is it safe to bake with moldy butter?

Most strains of fungi are killed when exposed to temperatures greater than 140-160 Fahrenheit, so it is understandable that you could assume if the butter is baked within a dish at such high temperatures, it would make the final product safe to eat.

This is not true, however, as not all mycotoxins produced by the fungi are killed by high temperatures, as they can survive temperaturesOpens in a new tab. such as those used in baking and cooking.

These mycotoxins or aflatoxins present in the butter, would be passed into the food, and once consumed could begin to cause any of the symptoms listed above.

Finally, once mold has been found growing on butter, it has almost certainly already spoiled or is very close to being spoiled. Its presence and the enzymes it secretes will also spoil both the taste and texture of the product, so no good cake or any other food item can come from using moldy butter.


Butter is more resistant to mold than other dairy products due to its high fat content and low moisture levels. It can still grow mold, however, and should not be consumed once this has occurred. Storing butter in an airtight container and refrigerating at 40 degrees Fahrenheit will preserve the product and slow the rate of mold and bacteria growth.

Over to you

I hope this article has helped you understand a little more about moldy butter and why you really shouldn’t try to use it, but now I’d like to turn things over to you. Have you ever used moldy butter, by accident or intentionally? Do you have any methods you use to keep your butter fresh for longer, or do you have any questions about this article? If you do, please leave a comment below and I’ll get back to you ASAP.

Chris Walker

Chris Walker has struggled for several years with mold after buying his own property. After finding the solutions to several issues around his home, he decided to create this site in order to answer as many questions about mold and mildew as possible to help others dealing with the same problems.

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