White crystals suddenly appearing on aged cheddar can look like mold, but they may simply be harmless calcium lactate crystals formed naturally as the cheese ages

Imagine opening your fridge to grab a block of sharp cheddar you've forgotten about for three weeks. As you take out the block, you notice some white crystals that have formed on the sharp cheddar's surface. Panicking, you wonder whether the block has gone bad or not. Would you throw the block away or scrape off the crystals and hope that everything else is alright? Before you decide to throw away a good block of cheese, here's something you should know. According to a 2022 UConn Extension article, it's entirely normal for these crystals to form, as it's simply calcium lactate, a harmless by-product of the cheese-making process, and not mold.

So, what are these crystals, exactly?

As cheddar ages, lactic acid produced by the starter culture reacts with calcium naturally present in the cheese to form calcium lactate, which then precipitates out as crystals once moisture levels drop during aging. This entire process occurs naturally as the cheese matures and becomes sharper. Naturally occurring calcium lactate crystals are most common in aged cheeses such as sharp cheddar.

Researchers have been studying these crystals that form on cheese for a while. In fact, a research article titled “Influence of Salt-to-Moisture Ratio on Starter Culture and Calcium Lactate Crystal Formation,” published in the Journal of Dairy Science, explains how factors such as the salt-to-moisture balance in the cheese and the starter culture's activity could affect the extent of calcium lactate crystallization. While it may sound more complex than it actually is, the information basically means that these crystals are a regular occurrence in cheese-making.

Why cheddar develops them, but other cheeses don't

Because of its high moisture content, mozzarella and other similar cheeses rarely develop calcium lactate crystals. Meanwhile, harder, drier cheeses such as sharp cheddar are more prone to developing these crystals. With that being said, it's entirely normal for your sharp cheddar to develop white spots, as it's a particularly hard and dry cheese. This would also explain why these types of cheeses are also particularly good at developing a sharp flavor.

Researchers have even been known to use X-ray diffraction to identify which specific crystals have developed in certain cheeses. A 2015 research paper titled “Crystal fingerprinting: elucidating the crystals of Cheddar, Parmigiano-Reggiano, Gouda, and soft washed-rind cheeses using powder x-ray diffractometry,” published in the journal Dairy Science and Technology, found that cheddar, parmesan, gouda, and washed-rind cheeses developed different crystal types, with calcium lactate pentahydrate being most common in cheddar cheese.

How to tell the difference between crystals and mold

Luckily, it's actually relatively simple to determine whether the white substance on your cheese is mold or calcium lactate crystals. Compared to the fuzzy, often multi-colored growths that are commonly found on moldy cheese, these crystals tend to be relatively hard and more 'gritty' to the touch. Additionally, the crystals that have formed on your cheese will most likely be found scattered on the surface of the cheese. If you can identify the white substance as gritty, hard crystals rather than fuzzy growth, it’s safe to simply scrape it away or eat around it; if you’re unsure whether it’s mold, discard the cheese to be safe.

Why cheese-lovers everywhere should be happy about this discovery

These crystals aren’t universally unwanted; in traditional and artisanal cheesemaking, the crunch they add to cheeses like aged cheddar and parmesan is often prized as a sign of flavorful, well-aged cheese. Large commercial manufacturers, however, tend to try to minimize them, mainly because mainstream consumers unfamiliar with the crystals often mistake them for mold and reject the product. So the next time you spot white specks on your aged cheddar, know that they’re likely just a natural (and in some circles, welcome) sign of a well-matured cheese.