Parmesan is an Italian hard cheese made from cow’s milk and used in a wide variety of dishes including soups, sauces and grated over pasta.
So, what are you to do when you go to your fridge to pick out your Parmesan to sprinkle over your pasta, only to find it has patches of mold growing on it?
Can it still be eaten? Is it dangerous? Why has the cheese got moldy in the first place and how can you stop it from happening again? In this article, we will be answering all these questions and more, so for all you need to know about Parmesan cheese mold, keep reading.
Why does mold grow on Parmesan?
Despite their low water content, hard cheese such as Parmesan can still grow moldy. Poor storage conditions (which we will be listing below), are the number one reason that you may find it growing in your Parmesan.
Fungi only need a few things in order to grow, including a source of nutrients, hydration, oxygen, and its desired temperature range (usually anything over 40 degrees Fahrenheit). By not following proper storage guidelines, you may find that you are inadvertently providing some or all of the list above.
Of course, the cheese in this circumstance provides the fats, proteins, carbohydrates, and minerals that mold needs. It consumes these nutrients by releasing enzymes that break the cheese down, and then absorbing them.
Should you leave your cheese uncovered, it is very easy for airborne spores to settle upon the cheese and begin a colony. Airborne spores or those from fungi formation on other items within the fridge can also spread onto the cheese, so ensuring it is covered correctly is very important.
Humidity levels greater than 55% are all that mold needs in order to thrive within a refrigerator. Most household fridges have an ambient humidity of between 30-50%, so all it takes is a few food items being put back into the fridge before they have properly cooled, or a jar of uncovered sauce being stored away to take the humidity past the point where fungi can use it as a source of hydration.
Many types of cheese “sweat” and release the moisture within them, so improperly storing a cheese like this in unbreathable plastic wrapping can create very high moisture levels around the surface of the cheese. When this moisture condenses, water droplets form which are an excellent source of hydration for both mold and bacteria.
Oxygen is everywhere, but by reducing the amount of direct contact cheese has with it, you can slow the rate of fungi growth considerably.
This is not to say that you want to completely starve your cheese of oxygen, as this would impact its texture and taste, but slight reductions will expand its shelf-life considerably.
Mold can grow at many different temperature ranges, with some falling into a state of hibernation in cooler temperatures, and some growing actively, even when in very cold temperatures. However, once the temperature climbs past 40 degrees Fahrenheit, fungi begin to grow and spread very rapidly. It is for this reason that you should check your refrigerator for any broken gaskets (seals), and to ensure the thermostat is working correctly and set to the correct temperature range.
What types of mold grow on Parmesan cheese?
The most common type or strain of mold you would find growing on Parmesan is penicillium. This strain is commonly found growing within soil, on decaying plant matter, on some dry cereals, and on many types of cheese.
As the spores can travel in the air, cross-contamination is the most likely way the spores would find their way into Parmesan, and this can happen at any stage of its production, from whilst the milk is stored in tanks, during transportation of the cheese or whilst on sale.
What does mold on Parmesan look like?
Spotting that Parmesan cheese has become moldy is not always as easy as it may at first sound. Depending on the temperature, it could take several days before white patches of growth would become visible.
However, once a strain has become established on the cheese, it may appear in several different colors and textures, which comes as a result of bacteria in your cheese. Using color and texture as a guide can help you to determine which strain you may be dealing with, but remember that many strains can appear similar at first glance, so without proper testing, you can only use color and texture as a rough guide.
With that, the following are descriptions of potential strains that may be growing on your Parmesan based on their color.
There are many strains that begin life as white growths (commonly referred to as white mold), and the coloration of these can change over time.
However, within the home (and likely to grow on food items), there are three common strains that appear white in color, these are Penicillium, Aspergillus, and Cladosporium. All three of these strains can be potentially hazardous to human and animal health, as we will discuss later.
To slightly confuse matters, all three of the strains mentioned previously can also present as either green or red depending on the environment it is living in, as well as at different points in their lifecycles. This is why it is important to conduct a test if you want to be absolutely certain of which strain you are dealing with.
A particular strain of penicillium (penicillium expansum), is likely to be the cause of blue mold growth on your cheese. This strain will usually begin its life as small patches of white cotton-like growth and change to a light blue hue over time.
Seeing black mold appearing anywhere in your home (let alone on your food), can be a cause for concern.
The most likely strain of fungi to cause black spots on parmesan is Aspergillus niger. This is a fungus that can grow with a dark brown to black coloration, and it certainly can cause health complaints if ingested or inhaled, but it is not the “true” Stachybotrys chartarum that you may see growing in other areas of the home.
Is Parmesan cheese mold dangerous?
Yes, although ingesting or inhaling small amounts of fungi formed on the cheese may be harmless to many, it does have the ability to produce mycotoxins that can cause very unpleasant symptoms, especially to those with suppressed immune systems or allergies.
The following is a list of the most symptoms can that can result from exposure to moldy cheese.
- Gastrointestinal discomfort
A further consideration is that it often forms on cheese once it has begun to turn rancid, this is also the point at which bacteria will become more prominent. Some of these bacteria strains can be particularly unpleasant, such as E. coli, which can cause food poisoning symptoms.
As it is very difficult to tell from sight alone which strain of mold you are dealing with, once moldy growths are spotted, they should be discarded.
Is it normal to see mold on Parmesan rind?
Spotting moldy growth on the rind of a wheel of Parmesan is not uncommon, as some cheeses are washed in brine and have strains deliberately added to them to enhance the flavor and texture of the cheese within.
The good news is that these molds are harmless to humans and will not make you ill if eaten. The mold you see growing on the surface of the cheese is more likely to cause Ill health.
Are white spots on Parmesan cheeses mold?
A very common sight on Parmesan is small white spots, which would be very easy to mistake for mold. In the vast majority of cases, this is not the case at all, but is, in fact, calcium lactate crystals. These crystals are not only entirely edible and harmless, but they are a signal of a well-aged, mature hard cheese.
To determine whether you are looking at mold growth or calcium lactate crystals, take a close look at its texture. If you were to touch the cheese, calcium lactate would feel gritty, like small salt crystals, mold, on the other hand, would feel soft and thread-like.
How to tell if your Parmesan has gone bad
Obvious signs of moldy parmesan, such as large patches of dark growth are not the only signs that your cheese has gone bad, or is in the process of doing so. The following are signs that the cheese is going bad and becoming rancid:
Surface cracks show signs of drying in the cheese. These cracks appear as the moisture content lowers, but can also be a signal that the amount of bacteria has also increased significantly.
Fresh Parmesan should have an intense, nutty smell. As it becomes rancid, the fats start to break down and will produce a more sour and metallic smell which may create a smell similar to that of blue cheese.
As well as smelling bad, unsurprisingly, rancid cheese tastes foul. The taste of rancid cheese is often described as being sour, bitter, and acidic. If you were to eat moldy parmesan, it is certainly safe to say you would know about it very quickly.
Slimy or sticky
Hard cheeses like Parmesan should usually be fairly dry on their surfaces. As cheeses sweat, some of this moisture will become present on the surface of the cheese and is nothing to be concerned about.
However, once the cheese gets to the point of becoming slimy, rather than just wet, it is a sign that it has become rancid and should be discarded.
Does fresh Parmesan get moldy?
Fresh Parmesan can indeed become moldy if stored improperly. Generally, a fresh unopened wheel of cheese will last up to nine months in a refrigerator, an open block will last for up to two months before turning rancid.
How do you keep Parmesan cheese from molding?
Whilst Parmesan does have a long shelf-life due to its low moisture content, as we have seen, it can still grow mold. However, as long as you store the item correctly, you can significantly increase its usability and preserve its taste and texture.
To prevent the cheese from going moldy, use the following tips.
Warm air rises in a refrigerator, so the coolest parts that suffer the least from temperature fluctuations are at the bottom.
If possible, store the cheese towards the back of the fridge, as this is the furthest point from the door, meaning it is less likely to be impacted by temperature changes whenever the door is opened or closed.
Use a salad crisper
If your fridge has a salad crisper, this is the best place to store leftover Parmesan as it has low humidity and more consistent, cooler temperatures. The drawer also keeps the temperature very stable even when the fridge door is opened and closed.
Keep it covered
Before putting your Parmesan and other cheeses in the fridge, wrap it in a layer of parchment paper, followed by an additional layer of either plastic wrap or aluminum foil.
The parchment paper will absorb excess moisture which creates a less hospitable environment for mold and bacteria, and the plastic wrap will prevent excess moisture from coming into contact with the cheese, as well as preventing smells from within the fridge from imparting their flavors.
Store it in a glass or plastic container
Keeping unwrapped cheese in your refrigerator is not advised, as it can dry out and become rancid more quickly. It can also take on flavors that may be present within the fridge from other foods, spoiling its taste.
Store any leftover Parmesan in a plastic or glass container with aluminum foil covering the top. This will prevent any cross-contamination and will allow the cheese to breathe without it drying out.
Additionally, the container will help to protect the cheese from temperature fluctuations, keeping it at a more consistent, lower temperature, and keeping it fresh for longer.
Freeze parmesan to preserve it
You may have realized that you have far more Parmesan than you can possibly use before it begins to turn rancid and turn bad. The good news is, you can freeze the cheese if needs be.
To freeze Parmesan, wrap it in parchment paper and place it in an airtight container. Whole cheese can be stored for up to one year, whereas shredded Parmesan and many other cheeses can be frozen for between 3-6 months before the quality becomes compromised.
Check the fridge temperature
To prevent mold growth on Parmesan, your fridge thermostat should be set to 40 degrees Fahrenheit or below. It is vital that you check your thermostat is set to the correct temperature, and that it is working as expected.
To check that your fridge is working at the set level, place a thermometer on one of the shelves and check regularly to ensure it maintains the correct temperature.
How do you know if shredded Parmesan cheese is moldy?
Spotting moldy grated or shredded parmesan can be tricky, as the affected parts can move within the bag and become hidden.
The first signs that you may notice would be a foul smell when opening the bag and clumping of the cheese. If you were to look closely into the bag, you may notice small amounts of blue or white growth within the clumped cheese.
How do you keep shredded Parmesan from molding?
As shredded cheese has a greater surface area, it is more prone to molding than cheese in a block. All the same rules for storing blocks of Parmesan apply to shredded Parmesan.
The following is a list of tips to store shredded Parmesan to prevent mold and bacteria growth:
- Store in an airtight container
- Store at the bottom of the fridge towards the back
- Freeze it
- Keep it in a ziplock bag and remove as much air as possible before placing it in the fridge
Despite Parmesan cheese being a hard cheese, it is still susceptible to mold. Poor storage conditions are the number one cause of growth, with penicillium being the most common strain found. Storing wrapped Parmesan cheese in an air-tight container in the bottom of the fridge towards the back, or in a salad crisper is the best way to keep it fresh. If you follow the steps outlined in the above article, you should not need to worry about dealing with moldy parmesan cheese.