Butter is used to add flavor to dishes, as well as being an ingredient in baking, a condiment, and as a way to fry foods. It has a long shelf life, but if not used quickly enough, it can still grow mold.
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?
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.
Does Milk Get Moldy And Is It Safe To Drink?
Can 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 types of mold grow on butter?
The most common strains of fungus found growing on butter are Alternaria, Cladosporium, and penicillium Roqueforti (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.
And finally, Penicillium Roqueforti has a dark green texture, sometimes with a slight blue twinge, and again has a velvet-like or powdery texture.
What causes butter to become moldy?
There are five main causes of butter becoming moldy, these are:
- Salt content
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, 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 own 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.
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 in order 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 between 45-50 degrees Fahrenheit. At this temperature, fungi cannot spread as quickly as they would at even a slightly higher temperature.
For example, the ideal temperature that mold can grow most efficiently is between 60-80 degrees Fahrenheit, 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.
Are the molds dangerous?
The Alternaria, Cladosporium, and Penicillium roqueforti mold strains all have the ability to cause health problems and in some cases, even medical emergencies if ingested, inhaled, or if physical contact is made with them.
Fungi have the ability to produce mycotoxins 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 symptoms:
- Breathing problems
- Skin irritation
- Watery eyes
- Runny nose
- Gastrointestinal discomfort
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. As soon as you see this occur, you should throw the butter away, as it cannot be saved.
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 hours, unsalted butter can begin to form mold, with visible mold patches becoming present within a day or two.
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:
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.
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 keeps 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.
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 butter 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 had mold on it is that some strains of mold can produce aflatoxins 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.
What happens in 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.
The symptoms listed above occur more within people that are particularly sensitive to the spores, such as asthmatics and people with suppressed immune systems.
If you discovered that you had eaten moldy butter and then do begin to suffer from new symptoms such as shortness of breath, nausea, or gastrointestinal discomfort, you should seek medical assistance.
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, it simply slows down their growth rate, and if cold enough, go into a state of hibernation until the temperature rises again.
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 strains are killed by high temperatures, as they can create heat-resistant spores that survive temperatures such as those used in baking and cooking.
The spores are also not the only concern, as if the mycotoxins or aflatoxins were present in the butter, these 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.