Help! There’s mold on my ferment!
This is the most frequent question I receive from people learning to culture probiotic and enzyme-rich foods and beverages in their home for the very first time.
Frequently, the email is tinged with concern and for good reason. Fermenting food takes time and costs money. No one wants to have to throw out a batch and start over! Discouragement is the number one enemy that prevents more households from adopting this traditional method of food preparation, despite the fact that it has the potential to enhance health so dramatically in a short period of time! Repeated failure with the fermentation process is one reason why.
Mold: Toxic in All Cases?
Mold, a type of fungus, is a scary word in our society today. It is associated with severe allergies and other life altering illnesses. There’s even an entire career path devoted to mold removal. Mold remediation vans can be seen driving around town during all seasons of the year. This was unheard of when I was a child. It seems more people than ever are sensitive to mold these days.
Prospective homeowners and renters now know to check a home or apartment for mold before moving in. And, if there is a water leak, some people choose to pull up stakes and move to another residence even after clean-up for fear of the health effects of toxic mold exposure. This on the off chance remediation efforts were not 100% successful.
Certainly, toxic black mold that grows under damp carpets and inside walls is something to be avoided!
But what about those fuzzy spots floating on the top of your fermenting jar of root beer, orangina, pickles or beet kvass? How about pink spots adhering to your sauerkraut? Should you be concerned about fermentation mold too?
The first thing to realize is that some things that seem moldy aren’t actually moldy at all ….
Is it Mold or Yeast?
It is very common for a white film that is mostly flat to sometimes form on the top of the liquid of a fermenting food. Floating white spots of foam might appear as well. In the case of fermented potatoes or sourdough starter, the film may be directly on the food itself. Many fermentation newbies immediately assume this is mold and discard the entire batch.
Mistake!
The white film or bubbles are actually not mold at all. It is a type of yeast called kahm yeast. Even though it may look dangerous and even smell odd, it hasn’t damaged the ferment. All you have to do is carefully skim it off. Once the yeast is removed, carefully smell and taste a small bit of the remaining ferment. If it smells and tastes fine, everything is a go. If it smells spoiled or rotten in any way, discard.
The good news is that most of the time, a film of kahm yeast on your ferment is not going to ruin the batch. However, next time you ferment, try to eliminate the possibly of yeast by taking the following precautions:
- Peel any root vegetables first before immersing in the fermentation brine. Leaving the skin on increases the chances of yeast growth (mold too!).
- Not enough salt and/or whey was added.
- The temperature in the home is too warm (around 72 °F/ 22 °C for 2-4 days is ideal). More time is needed if the house is cooler and less if it is warmer.
- The ferment is overexposed to oxygen. Using a fermenting jar with an airlock lid or using one or two fermentation weights will eliminate this problem.
What about if you have candida issues? Is eating a ferment where the kahm yeast was removed still safe? In my opinion, yes, it is still safe. If you have an extreme yeast sensitivity, however, you may feel more comfortable discarding the batch and starting over.
Be sure to use only airlock lids on your wide mouth mason jars or fermenting jars that come with an airlock lids in the future if you have a yeast sensitivity. Kahm yeast on a ferment particularly if you live in a warm climate is an all too common problem.
What to Do if the Ferment is Definitely Moldy
If the stuff on top of your ferment is not a thin layer of white, but something else entirely, chances are it is indeed mold.
Don’t panic! Your ferment might actually still be salvageable (but probably not).
Fermentation mold appears as fuzzy spots that may be a variety of colors: blue, green, black, pink, or even red. The spots typically adhere to the food that is above the liquid level inside the fermentation crock.
The spots may even appear on the culture itself as in the case of kombucha.
In over 15 years of home fermentation, I’ve honestly only had mold one time. This even though I live in hot Florida where my kitchen temperature is usually 75 °F or above, and I use only simple mason jars to ferment. The mold appeared on a kombucha culture, and I immediately threw the whole batch out, SCOBY and all. I would do the same if the fuzzy colored spots of mold appeared on the top of my sauerkraut.
I just don’t consider mold on food to be a good idea to consume – especially if a person is mold sensitive to begin with!
However, other friends of mine who ferment all the time disagree. They believe that it is fine to carefully remove the food layer that has the mold and consume the fermented food that is beneath the surface of the liquid (as long as it smells and tastes ok). They have done this for years and are still around to talk about it. So, mold on a ferment must not be that dangerous in reality! Certainly, scraping mold off the sides of a chunk of raw cheese and consuming the remainder is not problematic to health. I’ve done that many times when I’ve purchased large blocks of cheese from raw dairy farmers and didn’t consume it fast enough to prevent a bit of mold growth on the sides.
To Toss or Not to Toss (a Moldy Ferment)
Ultimately, the choice is up to you. Use your own best judgment in assessing whether the mold on your ferment is significant enough to warrant tossing the whole batch. If you are totally grossed out by colorful mold on top of your ferment (like I am), then just toss it and start over.
Next time, use a fermenting jar with an airlock lid or buy airlock lids for your mason jars and your moldy ferment issues will be a thing of the past.
Or, if you prefer to continue using mason jars without airlock lids, realize that fermentation is an unpredictable process and sometimes things go awry for no apparent reason. Chances are you won’t get mold again if you are using fresh, quality vegetables and the right amount of salt and/or liquid whey for the given recipe.
Do you have an opinion on whether it is a good idea to salvage a moldy ferment? Do you feel comfortable eating it or not?
Sarah, The Healthy Home Economist
Super informative! Thanks for letting us know all the ugly details behind mold and yeast! I think its important for everyone to know the differences and inform themselves on every aspect of these fermented microbes!
I am new to this. I love and I hope to do so for the rest of my years. I have a question, I made sauerkraut and it was great. However at the end of the bottle the liquid was very thick as baba. is it normal? or should I throw away it
Sorry, I don’t know what baba is.
Also instead of buying a air lock and lid, I simply use cling wrap and an elastic band. But I’m cheap
G’day Hannah, I’ve had this issue in the past too. I just keep an eye on it and top off with brine as needed. No worries.
Kind of gross to read about but really interesting to learn the differences.
A moldy ferment is luxury for the composte. Don’t cry about, be thankful! 😀
My grandma loved to finish jars of jams and compotes (yes, not even fermented, sugary stuff) that had real mold on top. She died at age 92. So I guess mold is not as toxic as believed.
I have experienced both of the problems that Hannah and Taryn mention. As for the disappearing-liquid problem in sauerkraut, I simply leave more room in my jars for liquid and add enough brine to cover the batch by at least 2-3 full inches, if not more. I’m not sure why it happens, either, but adding more brine seems to help.
As for the kefir issue (concerning the inconsistency – I’ve never had mold), I believe it has to do with the milk itself, although the quantity of starter used may also be a factor (I use starter packets myself, which helps control for that variable). Even using the packets, I still occasionally get watery batches, or ultra thick batches, without any other discernible variables changing. Since I purchase raw milk from a farmer, I suspect it has to do with the variability in the milk, since the milk (especially the fat quantity) can vary depending on the season. I have started making kefir with store-bought, non-homogenized milk – a local Montana brand – and seem to get more consistent results. Another strategy you could try if you’re after thicker kefir is adding a couple of tablespoons of heavy cream to your milk before culturing it. I’ve done this in the past and it has worked well; you just have to make sure to give it a shake every once in awhile so all of the cream doesn’t rise to the top and stay (which will exacerbate your mold problem).
I haven’t had a mold problem but I’m wondering if you have an idea why my sauerkraut always dries out. When I first make it I have lots of wonderful brine but it dries out after a few days on the counter. 🙁
I haven’t heard of this problem before. Is it dried out just on top or the whole jar is that way? Perhaps you need to pound the cabbage a bit more to get the juices out before packing in the fermentation jar.
Thank you for this article Sarah; it is all so interesting to hear what other folks do and recommend. Can you advise when making kefir as I don’t think I have ever made it correctly. It sometimes comes out not nice and fizzy or too thick or not fermented enough or sometimes even has the “mould” or the kahm yeast you referred to. I was told I was using too many grains for the milk quantity I was using but how to know how much to use? Thank you.
Fermentation varies quite a bit from batch to batch. I’ve not ever gotten kahm yeast on my kefir even when using a ton of live kefir grains for just a quart of milk (it just ferments faster so you have to watch it closely). Not sure what your problem there might be. Try getting some of those airlock lids mentioned in the post if you’re having too much variation from batch to batch.