Ever opened a pack of grated cheese and had it turn moldy on you, even before its expiry date? If so, you’re not alone!
As long as grated cheese is in its original pack, it can often be stored for weeks. However, once that pack has opened, some of the protection that the packaging offered is gone. Even if you carefully closed the bag after its first use, it isn’t as effective as it was before. Wondering why? It’s the gas inside the pack! This gas isn’t the same as the air surrounding you. That modified gas atmosphere is what helps keep your grated cheese good for longer.
Cheese & Molds
Cheese and mold are a common combination. Sometimes, it’s desirable, such as in a camembert cheese. Other times, not so much.
Those desirable molds are often (but not always) white in color, maybe a little fluffy. However, once you see small specks of blue/grey/green on your otherwise white or yellow cheese, you know something is off. These are molds that you don’t want on your cheese.
Cheese isn’t the only food that can spoil because of mold growth. A lot of foods can actually. Another very common example is (improperly packaged) bread.
For some cheeses, especially harder cheeses, you can simply carve off these moldy pieces and continue eating. However, if that mold has infested your grated cheese, you will have to throw it out. Because your grated cheese consists of smaller pieces, chances are it has spread pretty much everywhere quite quickly.
Why do molds like cheese?
Molds are just one type of microorganism that can occur on your food. Molds are pretty hardy, more so than most bacteria (another type of microorganism) that you may find in or on your food. Molds are living organisms and in order to survive they need food (often some type of sugar and maybe some protein), water (but not much), a good temperature, and most will need oxygen.
Improperly packaged grated cheese ticks off just about all these boxes, making it prone to spoilage.
Cheese happens to contain a lot of easily available food for molds. They contain plenty of sugars and proteins.
When cheese (from milk) is made water is pressed out to firm up and slightly dry the cheese. Also, salt is added, for flavor, but also to help preserve the cheese. On hard cheeses, such as Gouda, Emmentaler, and Edam, the amount of water is too low for most bacteria to grow. This is what enables us to store them for a long time. However, there still is enough water for molds to grow, be it a little more slowly.
Want to be updated on new food science articles? Subscribe to our weekly newsletter
You’ll probably store your grated cheese in the fridge. And whereas most molds grow more slowly in the fridge, they do still grow. Freezing grated cheese (at -18°C/0°F) will stop the growth of molds. However, keep in mind that freezing doesn’t kill molds. Once thawed the molds may start growing again.
How to prevent mold growth on grated cheese
So, grated cheese contains plenty of food and water for molds to grow. What’s more, by grating the cheese, the surface area of the cheese has increased significantly, opening up even larger areas of cheese that can be devoured by molds! So, how to prevent this growth?
That’s where the last factor for growth of molds comes in: the need for oxygen. The air surrounding us contains about 20% oxygen. By removing the oxygen, grated (as well as ungrated) cheese can remain fresh significantly longer. The best way to do this is by use a suitable packaging material.
In a vacuum pack, all air is pulled out of the pack, including the oxygen. As such, molds can no long grow. This method isn’t commonly used for grated cheese though. By pulling a vacuum on the pack, all the separate pieces of cheese are pressed against each other. As a result, when opening the pack the pieces can stick to each other or may form one large clump.
Modified atmosphere packaging
Luckily, it’s also possible to remove oxygen by replacing the air inside a pack with gas of a different composition. This is called modified atmosphere packaging (abbreviated MAP). During packaging, the equipment pushes out all the air and replaces it with other gases. Nitrogen is commonly used, as well as carbon dioxide. In some cases the pack might still contain some oxygen, just a lot less than is present in the air around us.
Modified atmosphere packaging is an invisible packaging technology that helps to extend the shelf life of wide range of food products! It is also commonly used for freshly cut fruits and vegetables, e.g. to prevent browning as well as par-baked breads.
The advantage of changing the composition of the gas in a pack of grated cheese is that you don’t actually have to change the cheese. Alternatively, manufacturers could have also added ingredients to the cheese that slow down or stop growth of molds, so called antimicrobials. If so, you will find those labelled on a pack of grated cheese.
Opening a grated cheese pack lets in oxygen
When a pack of grated cheese is opened, any protective gases will disappear. The composition of the air within the pack will be the same again as outside. The protection is over. As a result, once the pack of cheese has been opened, it’s a lot more prone to mold growth!
Why doesn’t grated cheese clump?
Clumping of cheese is not related to mold growth. However, you might have noticed that freshly grated cheese clumps a lot more easily than the store bought one. This is because most store bought grated cheese isn’t just grated cheese, it’s been modified slightly.
A common addition to grated cheese is the addition of some potato starch. The potato starch absorbs any excess moisture. It’s the moisture that causes the cheese to clump, so this gives a more free-flowing product.
In other cases manufactures may have developed a cheese specifically for grating. If that is the case they might have lowered the moisture content already, or otherwise changed the formulation to make it less prone to sticking.