The Big Cheese
Question: Why is blue cheese blue?
Cheeses come in all shapes, sizes and flavors, but only one cheese variety acquired its namesake from its color: blue cheese. The blue cheese category is packed with different cheeses, including favorites like Roquefort, Stilton and Gorgonzola — and they all share a very obvious blue hue. But, we really need to understand the process of making cheese before we can understand why some of them are blue.
So, the Cheese 101
As any lactose intolerant individual can tell you — cheese is a milk product. Others can likely tell you this as well, but this is a way to remind my lactose tolerant friends to count. your. lucky. genes.
But getting back to the point! Cheese is basically a fermented milk product and was the original way people preserved milk before refrigeration existed (AKA a long time ago, fellow cheese lovers). In fact, the first cheeses weren’t technically made by humans. Rather, the formation of cheese happened naturally, thanks to microorganisms, as milk sat in Neolithic containers. So, this leads me into the cheese-making process — and, for the love of cheese, please stick with me because we are about to get a little technical.
Cheese is made through three main steps.
First, increased acidity of liquid milk causes individual milk proteins, called caseins, to stick to one another, creating a solid intermediate called curds. This increase in acidity occurs when specific bacteria, such as Lactobacillus species, colonize milk and ferment lactose to produce lactic acid. This increase in lactic acid causes the surface of caseins becoming more neutral, helping them stick together, or aggregate. Curds are aggregates of casein.
Next, the curds are separated from the liquid that’s leftover after casein aggregation, called whey. The curds can then be heated, salted or pressed prior to being formed into wheels. At this point the cheese can be eaten, but please don’t make me link to a Cheezit commercial to remind you that it’s important to let cheese enter the third stage, where the real magic happens (it matures!).
In the last stage of cheese making, the cheese ages. During this time, certain microorganisms break down fats and proteins to release countless products that impart diverse flavors, while others form multispecies communities on the surface of the cheese, called the rind (that thing on the outside of brie and other cheeses that you always forget if you are supposed to eat it or not).
So that’s the cheese making process in a nutshell….or wheel?…or rind? The main take away here is that microorganisms (bacteria! fungi!) do things to milk to make it harden and taste super yummy.
Queso (K, so — get it??)…why is blue cheese blue?
While the majority of cheeses are aged using diverse bacterial species, the key element of the blue cheese aging process is actually a mold called Penicillium roqueforti. For better or for worse, this mold has several unique and interesting qualities that dramatically influence the flavor of blue cheese during aging*. Additionally — queue the drumroll — Penicillium roqueforti is a blue colored mold, and is what gives blue cheese its color.
The blue “veins” seen in blue cheeses are possible because of the ability of Penicillium roqueforti to grow in environments containing very little oxygen. Cheese makers take advantage of this quality by piercing holes into wheels of cheese (so small amounts of air can get into the interior of the wheel) allowing Penicillium roqueforti to grow into the interior of cheese, which gives these wheels their blue veins.
*As we all know, blue cheese has a distinct (gross) flavor, which can be primarily attributed to the presence of this mold but would require a separate post to go into detail. And the details are actually really neat.
So…the real question is: why is Penicillium roqueforti blue?
If you weren’t fully satisfied by that answer, you’re not alone. Do we know why Penicillium roqueforti is blue? Sort of. We know that Penicillium roqueforti produces a blue pigment. But what is this blue pigment?
Short answer: we don’t know.
As far as my research led me, we don’t yet know the identity of the blue pigment of Penicillium roqueforti. Full-time scientists think that this pigment is similar to the black and brown melanins found in other fungi, because inhibitors of black and brown fungal melanin production were also shown to prevent the blue pigment of Penicillium roqueforti. But, that’s really as far as these scientists have taken their investigations for now.
So, we don’t know the identity of the blue pigment in Penicillium roqueforti, but we do have some pretty good ideas of where to start looking. But next time you bite into a piece of blue cheese, I hope you’ll remember that it’s a mold that makes it blue.
Sources:
Gillot, G. et al. Functional diversity within the Penicillium roqueforti species. International Journal of Food Microbiology. 2017.
Wheeler, M.H. et al. The Effects of Tricyclazole, Pyroquilon, Phthalide, and Related Fungicides on the Production of Conidial Wall Pigments by Penicillium and Aspergillus Species. Pesticide Biochemistry and Physiology. 1995.
Button, J.E. et al. Cheese Microbes. Cell Press: Current Biology. 2012.
