There’s White Stuff Growing on Your Cheese That Isn’t Mold

Two weeks ago, one of my best friends and ex-cheese comrades, Chelsea, brought our old mentor/boss-lady, the illustrious Kim Martin, into the shop. Neither of them had visited us before, and it was pretty exciting to show them around our little corner of the co-op.

As they were getting ready to leave, Chelsea pulled me aside and silently pointed at a quarter-wheel of aged Gouda on display in the back of the case, tapping the side of it to show me that it was all white.

“It’s not mold,” I announced without skipping a beat. “It’s calcium lactate.”

This is something I actually have to write on the scale label when we wrap wedges of the cheese for sale, because people are inherently put off by a sheet of white on an otherwise butterscotch-orange cheese.

After all, most people are familiar with white, wispy molds growing on the outside of cheese—either as the well-manicured coif of a bloomy-rind cheese or as errant growths on the cut face of half-eaten cheese hunks living in the refrigerator cheese drawer.

But there are other white things that can grow on your cheese, and they are actually desirable: crystals!

You know what I’m referring to if you have bitten into an aged Gouda, Cheddar, or Parmesan and felt that satisfying crunch. You also know it if you’ve sunk your teeth through the sticky orange exterior of a washed-rind cheese and felt a slight grittiness.

People often come into the shop looking for cheeses that have “salt crystals” in them. As you will learn below, there are two “families” of crystals that form in cheese. Only one of those families has anything to do with salt—and those are not usually the ones people go hunting for in a cheese shop. While a cheese might taste salty and have crystals in it, that doesn’t mean the crunchy bits are salt, per se.

The crystals that people really want when they are asking for “salt crystals” are often referred to in the industry as “flavor crystals.” That’s because the sight of these crystals is a sign that you’ve found a flavorful, or fully-developed, cheese.

In fact, cheese crystals don’t have any effect on the way a cheese tastes—they are flavorless and scentless. But they do affect other sensory perceptions of a bite of cheese: sound (crunching), touch (bumpiness or rough texture), and sight (white spots, clusters, or patches).

There are several different types of crystals that grow in or on cheese at different times in the cheese-making or -aging process. They are either going to be the product of mineral (salt) emulsion during cheesemaking or protein breakdown (proteolysis) as the cheese ages.

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The crystals you may not notice as much are the “inorganic crystals,” or crystals formed by minerals.[i] This “family” of crystals is created when salts emulsify, or disperse throughout the cheese without dissolving, during the cheese-making process.[ii] (These are the ones you could call salt crystals.)

For example, calcium phosphate crystals are most commonly found under the rinds of bloomy-rind cheeses, helping them become soft as they ripen.[iii] Two other kinds of inorganic crystals, Ikaite and Struvite, are what you notice when a washed-rind cheese has a gritty rind; Ikaite crystals are formed from calcium carbonate, whereas Struvite crystals come from magnesium ammonium phosphate.[iv]

The crystals that are most noticeable in cheese are the “organic crystals” that are formed by the breakdown of amino acids during the cheese-aging process.

As a cheese ages, it loses moisture and its protein structure contracts and stretches. As this happens, the amino acid chains running through the cheese that make up that protein structure start to break up; the whole process of protein breakdown is called proteolysis.

Each type of organic crystal that you will find in a cheese is named after the amino-acid chain that broke up to create it.

For example, tyrosine crystals give aged goudas their famous crunchy texture. They can grow inside the paste of cheese, or all around the little holes inside a cheese.

Leucine crystals have a similar effect, but have a more diffused, smear-like appearance than tyrosine crystals. Both of these types of crystals may be found in goudas, Alpine-style (Swiss) cheeses, and Grana-style cheeses (e.g., Parmigiano Reggiano, Grana Padano, Piave, etc.).

And then there is calcium lactate, which frequently forms on the outside of rindless cheddars as they age. Calcium lactate formations are seen as a sign that the cheese has aged for a long time and should have a more developed flavor profile.

Calcium lactate originates from an earlier stage of proteolysis, when lactose is still present in the liquid milk that will be fermented into cheese. As the bacterial culture in the cheese eats up all of the lactose, or milk sugar, in the milk, the bacteria create lactic acid. [v] Calcium lactate is a byproduct of that lactic acid interacting with calcium carbonate in the cheese over time.

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Just in case you were wondering what calcium lactate has to do with amino acids, lactic acid bacteria convert the proteins in cheese into peptides, and then into amino acids (like tyrosine and leucine).

You can find several types of crystals on the same cheese—tyrosine and leucine crystal deposits on aged Parmigiano Reggiano, for example.[vi]

So how you do know which is which?

Generally speaking, calcium lactate will be found on the outside of a cheese (usually a cheddar), and tyrosine or leucine crystals will be on the inside. Calcium lactate can also form on the inside of cheese, but tyrosine and leucine crystals cannot.

Tyrosine crystals will be hard and crunchy, whereas calcium lactate will be slightly softer, and sometimes almost powdery or flaky, in comparison to tyrosine or leucine crystals.

Calcium phosphate, Ikaite, and Struvite crystals will be found on any “mold-ripened” cheese: you may notice them in the slight grittiness at the rind of a bloomy rind cheese, like Brie or Camembert, or a washed-rind cheese, like Epoisses, Chimay, or Grayson. (Washed-rind cheeses, also called “smear-ripened cheeses,” fall into the mold-ripened category because their rinds are created by a complex ecosystem of molds and yeasts.)

What all of these crystals have in common—other than the texture they create, of course—is that they signify age in a given cheese. They help mold-ripened cheeses become soft, and they let you know when a hard cheese has been nicely aged.

So if you peel open a chunk of Cheddar and find white deposits marbling its outsides, rejoice! You’ve gotten a well-aged cheese that is bound to taste delicious.

And if you crack open a wedge of Gouda, Gruyere, or Parmigiano Reggiano and see little white spots either riddling the paste or clustered around the cheese’s eye holes, also rejoice! You’ve got tyrosine or leucine crystals, and that cheese’s texture is going to be like cheese candy.

(Cheese candy, good readers! Could you wish for anything better?)

The moral of the story? If you see white on your cheese, don’t just throw it away. Touch the white stuff to see if it’s hard or soft. If it’s soft, it’s probably mold (and you can just cut it off of a firm cheese). If it’s hard, it’s a precious little colony of crystals, and you have hit the cheese jackpot.

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[i] Tansman, Gil Fils. “Crystal.” The Oxford Companion to Cheese. Ed. Catherine Donnelly. New York: Oxford University Press, 2016. 205-6.

[ii] Polowsky, Pat. “The Wonderful World of Cheese Crystals.” Cheese Science Toolkit. https://www.cheesescience.org/assets/doc/crystal_handout.pdf. Accessed 4 Nov. 2018.

[iii] Tansman, 205-6.

[iv] Polowsky, “The Wonderful World of Cheese Crystals.”

[v] Polowsky, Pat. “Lactose and Lactic Acid.” Cheese Science Toolkit. https://www.cheesescience.org/lactose.html. Accessed 4 Nov. 2018.

[vi] Johnson, Mark. “Crystallization in Cheese.” Dairy Pipeline, vol. 26, no. 3, 2014. Wisconsin Center for Dairy Research. https://www.cdr.wisc.edu/sites/default/files/pipelines/2014/pipeline_2014_vol26_03.pdf. Accessed 4 Nov. 2018.

3 thoughts on “There’s White Stuff Growing on Your Cheese That Isn’t Mold

  1. Interesting! I got a little lost in all the details of the salts/crystals, but now I know if the white spots are hard it’s probably not mold! Any other ways to differentiate? (We need to have a ‘cheese party’!!

    1. Ah, sorry about that. I was hoping to make the science easier to understand in a short format. The texture is the biggest thing to know–hard for crystals, soft for mold. The only possible exception I can think of might be when the outside of a cheese is all white and orange or brown if the cheese was bandage-wrapped (wrapped in cloth and a fat like butter or lard), like a traditional Cheddar. But then it might be a little stickier, so “hard” won’t quite fit the mold texturally. When in doubt, ask a monger!

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