I recently had a question from a newsletter subscriber about the cheesemaking microbe Geotrichum candidum. Specifically, the person wanted to know sources for the fungus for cheesemaking. Rather than try to answer this lengthy topic in an email, I decided a post on the subject might be fun to write.

There are two very important things to remember when it comes to cheesemaking flora:

• They are everywhere! All of the aged, or ripened, traditional cheeses made throughout the world came about because of native, natural microbes—from lactic acid bacteria to ripening surface flora—were present at that moment.
• All microbes involved in making cheese work in shifts, in successive populations that more or less make the cheese a great environment for the next wave.

Let’s talk about these two facts in regard to Geotrichum candidum, or as it is affectionately known amongst cheesemakers, Geo. But first, what is it?

What is Geotrichum candidum?

In the vast kingdom of fungi, you have life forms such as mushrooms (the visible fruiting bodies of an unseen fungus), yeasts, and molds. Yeasts and molds play an active role in the ripening (the stage after curd is formed and salted) of cheese. Geo is a fun little microbe, as it is most closely related to yeasts, but many strains grow with mold-like characteristics, sprouting fuzzy filaments (mycelium) on the cheese surface. It’s been such an elusive fungus to categorize, in fact, that over the two-centuries-plus since it was first identified in 1809, it’s had over 100 names and multiple changes in classification!

For cheesemaking purposes, you can think of (and buy) Geo in three forms: yeast-like, mold-like, and in between—called intermediate. Here are the known differences in these three types:

• Yeast-like: cream colored, smooth appearance, low proteolysis (protein breakdown), low de-acidification, ideal growth temperatures of 22-25 C (72-77F), but the usual temperature of use is 10-15 C (50-59 F).
• Mold-like: white colored, fuzzy appearance, high proteolysis, high de-acidification, ideal growth temperatures of 25-30C (77-86 F), but usual temperature of use is 10-15 C (50-59F)
• Intermediate: In between in all characteristics.

You might have noticed that the ideal growth temperatures listed above are quite high (I hope you noticed…) But yet during the making of surface ripened cheeses we do not aim for these temperatures. You might have already guessed that’s because we don’t want them to entirely take over the cheese! But keep these ranges in mind, particularly if you are having problems with the succession of yeasts to molds in the making of your cheeses.

Regarding ideal pH for growth, each of the above forms has the same range: pH 3.5-5.5. Keep in mind that at each end of this spectrum, the rate of growth will slow. Salt levels that favor Geotrichum c. are between 1-2%, fairly low, meaning salting must be done quite carefully. Here’s a fun fact that has nothing to do with white mold ripened cheeses: Saint Nectaire a washed rind French cheese, counts on Geo, but is more heavily salted. To work around this, the pressed curd is dry salted, then, after 24 hours, it is rinsed, allowing the surface to become a favorable substrate for the growth of Geotrichum candidum. Cool, eh?

Sources for Cheesemaking Geotrichum c.

Going back to what I said earlier, in traditional cheesemaking Geo was simply present in the milk and environment, particularly the aging space, of the cheesemaker. Like many beneficial cheese microbes, Geotrichum candidum strains are abundant in the environment. In addition, the different strains within this species are, according to research, by Mother Noella Marcillino and others, “immense”. In her study of the microbe, she sampled 180 sources and within those found 64 different strains. That’s an indicator of enormous genetic diversity—which is awesome for cheese terroir, but also a source of frustration for those seeking to duplicate a specific cheese. This is one reason I’ve always encouraged the following, “Make a lot of different cheese types and then, over time, see what you, your milk, and your environment can make well.” In other words, let your own terroir dictate what you make, not a beloved recipe or whim!

Geo species and strains are found in soil, on skin, on plants, and on all the surfaces these things come in contact with. Geotrichum candidum lives alongside yeasts, bacteria, and virus in kefir grains. It’s found living in successive generations of some milk ferments, such as villi (see my book Homemade Yogurt and Kefir for more on both of these ferments). Geo grows on charcuterie such as salami, on vegetables and bread left to sit. If you cut a slice from a cheese such as store-bought Brie and rewrap it, chances are, Geo and other white molds will grow right across the cut surface! I’m hoping you’re getting the idea!

If you approach your cheesemaking from a less sterile, industrial standpoint, then you will find Geo checking out the surface of many naturally aging cheese in your aging space. Its presence is NEVER a bad thing! I used to love watching the cheeses go from pure white, to mottled and rather a “mess” (this I called their gangly teenage-stage) to fully patinaed: rustic, gorgeous, and always filled with nuance.

Then, of course, you can buy commercially prepared and “focused” strains from culture manufacturers. Within this option, there are also myriad choices—providing you turn to a commercial supplier rather than a company focused on novice, home cheesemaking. But if you do, don’t be surprised to find that the more you investigate the topic, the more confused you might become. One of my favorite presentations to give is on the art and science of bloomy rind cheeses. There are so many choices a cheesemaker can, and often needs, to make to perfect their cheese—and help it stand out. But, as always, in the beginning don’t overthink it.

If you work with pasteurized milk, the selection of these commercially available ripening cultures becomes more critical—especially if you are marketing them. In that case, it’s worth downloading pdfs on each manufacturer’s ripening products and reaching out to an expert at a company such as Dairy Connection or Fromagex (two of my favorites).

Geo options from Danisco

Geo options from CHR Hansen

Succession Planning for Bloomy Rind Cheeses

Now let’s cover the topic of microbes thriving in successive waves in and upon a cheese. This is true in other settings from fermentation to spoilage. In regards to cheese, think of how lactic acid bacteria play the first role, diving right in and consuming lactose, leaving behind lactic acid. Eventually, they die off, contributing enzymes in their cell walls that contribute to breaking down proteins and fats. There’s an overlap of populations, though, so don’t think about in in clear cut terms. Many microbes lay dormant in milk and in cheese, waiting for the right conditions for growth—or growing very slowly. If the conditions are too harsh you might never see the desired results! Mold ripened cheeses, such as reds, whites, and blues will give you the biggest challenges for controlling these conditions. I could seriously talk about this for days (and I still have tons to learn myself!).

Geo, being truly a yeast, is able to grow earlier in a white bloomy cheese’s life than the true white mold, Penicillium camemberti. Other yeasts, such as Debaryomyces hansenii, can grow even earlier. Both of these play the role for setting the stage for P. camemberti (in other cheese types, they play a slightly different role). I won’t go into any of those here, but, again, keep this in mind if your cheese takes a turn you didn’t expect.

Succession planning requires knowing the conditions that favor the microbes you want or expect to take hold. So, the manipulation of starting pH, salt levels, temperature, humidity, and so on are key to what happens on the surface of the cheese (and inside, too, of course!)

Conclusion

Our lovely, fuzzy friend Geo is everywhere, waiting to step in if we provide the right conditions. Using commercial ripening cultures is a great way to hedge your bets and develop a unique product. If you are dealing with rind issues—too thick and rubbery being a very common one—changing the Geo you’re using is a possible remediation. And no matter what, know that working with white mold cheeses is one of the most challenging categories of cheesemaking, both from the making and from the marketing standpoint. You’ve got to love them to succeed.

If you come to any of my classes, bring your examples!

Happy Cheesemaking! GC