Science Byte

Why do some soft washed rind cheeses get a sandy/gritty rind?

Let’s get this out of the way upfront – IT’S NOT SALT! While on a flight yesterday, working on a cheese presentation, the person next to me mentioned how much they loved "stinky" washed rind cheese. The inevitable gritty rind discussion came up, and prompted this post. Washed rind cheeses can often have a gritty rind, and lots of popular press sources seem to blame it on salt. (examples here, here, and here) It’s an easy trap to fall into since these cheeses are often washed with a brine solution during aging (thus the name: “washed rind”), but the cause of the grittiness is much more interesting. Salt crystals aren’t to blame, but other even cooler crystals are the cause of the grittiness.


You can see the crystals sparkling on the surface of this cheese.

Thus far, a few types of crystals have been found on the surface of washed rind cheeses. The main ones being calcium carbonate, magnesium ammonium phosphate, and calcium phosphate. You can take a look at this paper for more information. I should mention there may be multiple forms of these crystals, but let’s just talk about it broadly. You’ll notice sodium chloride isn’t mentioned (i.e. salt).


An example of some magnesium ammonium phosphate crystals. Here they're being seen under some filters, in reality they are just transparent.

The surface bacteria that are growing on rinds of these cheeses deacidify the cheese. As the acidity goes down (i.e. pH goes up), this can cause minerals to precipitate and form crystals. All the necessary pieces of these crystals are easily available when making washed rind cheeses. Calcium, phosphate, and magnesium are all found in milk and cheese (and water to some degree). Carbonate and ammonium are fancy words for carbon dioxide and ammonia gas, which are naturally created by the surface microbes as these cheeses are aging. You add all these together, you’re left with a gritty rind!

Note: this post is about soft washed rind cheeses like Taleggio or Époisses. There might be other things going on with firm washed rind cheeses like Gruyère, no one's looked into the rinds of those yet.