Is green mold good or bad? I've asked that question myself dozens of times over the past decade or so that I've been curing meats and sausages. Up until recently, I would reject any mold other than white, green included. It was fear that guided me. My fear was the result of a lack of knowledge. But now, I've changed my mind. My new batch has green mold on it, and I am just fine with it. I actually dig the look.
But what do we know about green mold? Is all green mold good or bad? Or some green molds are good, and some are bad? Is green mold avoidable? I now seem to have a clear answer to those questions.
Why and when green mold appears?
Up until recently, I dry cured my salami at the standard 55F / 75% RH. Green mold rarely appeared on my sausages, which were inoculated with white mold. I use naturally occurring white mold collected from previous batches. When inoculated with a more active Mold-600, chances of green mold appearing are practically zero. Here is a picture of Fuet that I finished just recently. It was cured at 76%-78% RH and, as you can see, there is not a hint of green mold on it.
My current batch is maturing at 55F - 57F and 80% - 86%RH. Despite inoculating with white mold which appeared pretty quickly, if a little patchy, I began to see areas of green mold soon after. The green mold initially appeared around the damper areas, like the creases caused by the twine. I wiped it with a 50/50 mix of white vinegar and distilled water. A week later, the green mold appeared in many other areas. There was a lot of it too. Is it a disaster, or is it a normal part of curing salami at a higher humidity?
Now, green mold can also happen if the environment or the casings are contaminated with the green mold spores. I am going to rule out this possibility simply because I sterilize my curing chamber with bleach before every new batch, and I am very particular about cleanliness when working with meat. Every tool I use to process meat gets treated with a solution of bleach, gloves, etc.
Is green mold avoidable?
I would say yes. In general, the higher the humidity, the more molds, including green, will appear. Most, if not all, of my batches, dry-cured at 75%-78% RH did not develop green mold. As such, I can confidently say that high humidity is the cause. By lowering the humidity, you can almost certainly avoid green mold. This is assuming that the environment is not contaminated with green mold spores.
Is green mold good or bad though?
Now, this is a million-dollar question. I am trying a new approach where my salami are matured at higher humidity. This is new to me but is commonly done in Italy and many other places I presume. I have the green mold on my sausages. What do I do? The answer is: IT DEPENDS.
Patchy, bright green, hairy, nasty looking, bad smelling mold is bad. Here is an example of bad green mold.
Is there a good green mold? Certainly. The typical white mold that we see on salami is Penicillium nalgiovense. However, in recent years, scientists found a different strain of mold from the Penicillium family, Penicillium salamii. Like the common white mold, this particular mold has a green color and does not produce mycotoxins, toxic substances that can have harmful effects on human health. In fact, this green mold is found on salami all over the world.
On the other hand, when the commonly found white mold - Penicillium nalgiovense - blooms, or grows aggressively, it acquires green color. That's why we see pictures of salumerias showcasing cured meats and sausages covered in green mold. Photo's below are courtesy of eGallet forums. They have an interesting discussion on green salami mold there.
Here is another interesting image of salumi covered in green mold, typical of cellar-matured meats at about 80-85% Rh:
How to tell good green mold from bad?
That's another million dollar question. Searching the internet for the images of Penicillium salamii produced basically nothing. The only reputable source I was able to find was the Federation of European Microbiological Societies that had an article on Penicillium salamii strain ITEM 15302. Luckily, it had a fantastic illustration of Penicillium nalgiovense and Penicillium salamii after 7 and 13 days of seasoning (maturing).
As you can see, both strains exhibit green color, though Penicillium salamii is more of creamy, light green. I am surprised about the green color of Penicillium nalgiovense though. But it looks like the color changes over time. Perhaps humidity affects that as well.
A butcher-friend from Italy, when asked about what he thought about green mold, said this: white mold, the favorite for cured meats, is the first to appear on salami, but is very weak and during the long maturation phase tends to disappear to give way to more aggressive, gray and green molds. But those molds do not create problems; you only need to worry if yellow or black ones appear. However, the molds must be smelled to understand if they have unpleasant smells that we would then find in the product. Smells of pepper, earth, peas, potatoes, mushrooms, camphor, peppers, moldy cellar are good. Naturally, molds that give off unpleasant smells must be removed by brushing them off.
Green mold on my salami
After fermentation and drying at low humidity for 7 days, my salami entered maturation stage. As I mentioned above, I will be maturing them at 55F - 57F and 80% - 86%RH. I noticed green mold on the second day in a few spots. I wiped it off with a vinegar solution. A week later, I see green mold everywhere.
It's different though. It has the same texture/feel as white mold. It's chalky, powdery.
Comparing to the pictures of the Penicillium nalgiovense and Penicillium salamii above, it looks very similar to Penicillium nalgiovense. I compared the smell of the green mold and the white one, and they both seem to smell the same. I could not tell any difference. Needles to say, I am quite comfortable with leaving this green mold as is and I can't wait to see how my salami look and taste after they fully mature.
Update on green mold two weeks later (April 18, 2020)
Two weeks later my green mold is practically gone. I can now confidently conclude that it was, in fact, Penicillium nalgiovense. The green coloration was caused by blooming that occurred during the initial stages of mold growth.
More examples of good green mold
I did some digging around and was able to find more examples of good green mold that looks similar to mine. These don't seem very widespread, I am curious to know why.
From Biocoop Cestas
From Le blog Saucisson
From Ferme Chazal
From Boucherie Senegas