We've all been there. You were busy the last couple of weeks, but now you're finally ready to bake some homemade sourdough bread again. You pull your starter jar out of the fridge and notice it looks...funky. Crusty. There are things on top of your starter. And the smell is just off. There are plenty of things that can develop on a neglected starter or any starter really, if the mix of conditions is just right (or in this case, wrong). What does mold on the starter even look like?
In this post, we'll go over the following:
- MOLD AND ITS MANY FORMS
- WHY IS IT IMPORTANT TO DETERMINE IF YOUR STARTER IS MOLDY?
- WHY DOES MOLD DEVELOP ON THE STARTER?
- WHAT DOES MOLD ON A SOURDOUGH STARTER LOOK LIKE?
- MOLD OR BACTERIA?
- EXAMPLES OF MOLD (PICTURES)
- EXAMPLES SIMILAR TO MOLD, BUT NOT MOLD
- MY SOURDOUGH STARTER IS MOLDY. NOW WHAT?
- HOW TO AVOID MOLD ON THE SOURDOUGH STARTER?
MOLD AND ITS MANY FORMS
The good news is you've come to the right place! In this post, we will focus on mold only. There will be other issues mentioned in the sense that they are NOT mold. But mold will be the star of the show, as it can present itself in many forms on the starter. I have conducted a bit of research and reached out to people who had issues with mold. I did not yet manage to get mold on my starter, but I realized it is a common problem. With the help of the pictures and information below, I think you'll be able to determine whether or not your starter is in fact moldy.
Disclaimer: I am not a microbiologist, nearly a sourdough enthusiast who likes to do her research. The pictures below are used with the consent of its owners and are showing different examples of what the starter can look like when it is contaminated (or only dried out, hungry, etc). Since the cultures from the pictures were not actually tested n a lab, we can never be 100% sure what they were. But they are good to give you a general idea. It is always your decision what to do with your own sourdough starter. And again: when in doubt, toss it! You can create a new, active sourdough starter in a matter of weeks, so why risk your health?
WHY IS IT IMPORTANT TO DETERMINE IF YOUR STARTER IS MOLDY?
Because the majority of other issues starters oftentimes develop are completely salvageable. Mold, on the other hand, is not. There is information out there about how to revive a starter that was contaminated by mold. They claim that if mold is located only on the surface or on the sides of the jar, you can still save a bit of starter and go from there. In my opinion (which is based on reading a lot of scientific articles that address molds and their effects on health), this is risky.
True, the majority of molds are not toxic at all, but some are! And without access to a lab and testing equipment to determine which mold specifically is growing in our starter, we have no way of knowing if it is harmless or not. I think it is better to err on the side of caution and throw away any starter that starts to show signs of mold.
Starting a starter from scratch is not too difficult and if it is any consolation: making the first starter from scratch is harder than making subsequent ones. That is because there is only a small amount of microorganisms that your starter needs to thrive present in your kitchen. But if you were using sourdough starter and baked with it, the amount of those microorganisms in your kitchen is higher and they'll find their home in your new starter more quickly.
WHY DOES MOLD DEVELOP ON THE STARTER?
Mold likes a moist and warm environment, so sourdough starter seems like a nice place for it to thrive in. The sourdough starter itself is a mix of wild yeasts and good bacteria. Compared to commercial yeast (the strain named Saccharomyces cerevisiae) there is not only one wild yeast present in your starter. There are lots of them, along with beneficial bacteria, mainly lactic acid bacteria and acetic acid bacteria. Think of your healthy sourdough starter as a whole ecosystem. So Why doesn't mold always join the party in a jar?
Because the lactic acid and acetic acid bacteria in the starter produce (you guessed it) lactic and acetic acid. That is why sourdough starter can sometimes smell very acidic, so much so that it reminds of nail polish remover. They make sourdough starter very acidic and unfriendly for bad bacteria or mold to contaminate it. A healthy starter that is established and fed fresh flour regularly will manage to fend off unwanted microorganisms. This is why mold is usually a problem when a starter is young and the colonies in it are still finding an optimal balance. A mature starter has less chance of being contaminated because the microorganisms in it are living in a perfect symbiotic relationship. Also, if the starter is receiving regular feedings, the organisms in it thrive and can fight unwanted visitors better.
The bottom line is, a starter that is very neglected (hasn't been fed for a long time) or very young has a greater chance to develop mold.
WHAT DOES MOLD ON A SOURDOUGH STARTER LOOK LIKE?
Mold on a sourdough starter typically ranges from white to darker greenish-brown and is always at least a little fuzzy (but it is sometimes difficult to see the fuzz). It can also be yellowish or bluish in color. As a general rule, if there is growth on your starter that is even slightly fuzzy, it is mold. The starter will also likely have a very unpleasant smell.
The presence of mold on top of the starter can look very different from one case to another. That can make guessing if there is a tiny bit of mold or if it is something else on the surface of a starter very difficult. With the help of many sourdough enthusiasts from sourdough Facebook groups, I have put together some pictures that show moldy starters and some that look very similar to mold but are not mold. That way you can compare your starter with the starters on the pictures to determine if you have mold on top of your sourdough starter or not.
MOLD OR BACTERIA?
Pink or orange streaks in the starter are typically not caused by mold (but sometimes they can be!) but by other types of harmful bacteria. Pink hues on a starter are usually caused by a harmful bacteria called Serratia marcescens. If your starter has orange or pink streaks in it, you have to throw it out. Pink and orange streaks are fairly easy to notice and there is usually no doubt whether they are present. If you are unsure, the best way to go is to feed your starter a couple of times, leave it at room temperature, and you'll see if they get stronger. If so, you have a bad sourdough starter. Whether they are from mold or other types of bacteria, starters with pink or orange streaks need to be discarded.
EXAMPLES OF MOLD (PICTURES)
1. Dark green, dark brown, or almost black
1. Dark green, dark brown, or almost black
Let's start with the most obvious case. When you see dark fuzzy spots, you can be sure that's mold. The spots can be dark brown, dark green, blue, or almost black. Mold on sourdough starter will most often look like the examples below.
2. Dirty white
Sometimes mold will take the appearance of dirty white spots or patches. In those cases, it is sometimes difficult to distinguish from kahm yeast, because they can look very similar (see "kahm yeast" below for pictures). The main difference is that mold patches will usually also be fuzzy,
3. Yellow or blue
Strong yellow and blue hues in your stater indicate contamination that is not normal. It is advisable to discard a starter that has anything yellow or blue in it. The yellow patches can sometimes appear due to the starter being very dried out (see "dried-out starter" for pictures).
EXAMPLES SIMILAR TO MOLD, BUT NOT MOLD
The number one reason for worry is usually something completely harmless: hooch. Hooch is dark grey, sometimes even black liquid that collects on top of your starter. It's only a by-product of fermentation; wild yeasts in the starter are breaking down the food (flour) and in the process, they are creating alcoholic liquid or hooch. It also has a very unpleasant odor, very acidic. The presence of hooch on your starter means that it's hungry and needs to be fed. Some people like to stir the hooch in before feeding, some don't. I personally like to pour mine off. I find that sourdough bread tastes more sour if the starter had hooch mixed in.
2. Dried-out starter
If you expose the starter to air (you have it covered only with a cloth/a loose lid) for a long time, it can become dry and crusty on top. This film tends to look a bit too yellow for your comfort, but it does not mean anything is wrong (yet). The example in the photo below is a dried-out starter, and the white spots are flour. They are not fuzzy!
2. Using rye flour can make the starter look reddish
Some people have pointed out that using rye flour in their starters tended to give the starter a reddish tone. So before you toss your rye starter, google some pictures and determine if the red you're seeing is normal or not.
3. Using pink Himalayan salt
Before panicking due to rink spots in your dough, think about which salt you used! If it was pink Himalayan salt, the starter is just fine and the pink color was a consequence of the salt used.
4. Kahm yeast
Although not technically a scientific term, "kahm yeast" is a common answer in sourdough communities. It refers to a growth of a pellicle on the surface of the starter. The pellicle is produced by different types of yeast and bacteria, most of which are harmless, but some are not! The advice in case of having "kahm yeast" on your starter is to scoop it off and take good care of your starter. I advise not to do that due to the (albeit small) possibility of food-borne illness resulting from bad bacteria/yeast. "Kahm yeast" is not mold, but it can be harmful, so caution is advised.
MY SOURDOUGH STARTER IS MOLDY. NOW WHAT?
The bad news is that a moldy sourdough starter means you'll have to say goodbye to your old starter and make a new starter (or get a new one). Visible mold, even a teeny tiny bit, means mold spores are probably already contaminated your whole starter, even if you don't see them yet. Get a new jar; don't use the previous one without cleaning it thoroughly! You'll need to make a new sourdough starter.
HOW TO AVOID MOLD ON THE SOURDOUGH STARTER?
Having to deal with a moldy starter sucks, so you're probably asking yourself, how to avoid mold in the future. Unfortunately, not all factors are in your control. Mold is present almost everywhere, it's just a matter of how favorable the environment is for it to start thriving somewhere. You can take some precautions to lessen the chance of mold contaminating your starter, but sometimes it's just a case of bad luck. If the flour you buy has a lot of mold spores in it, there's a chance it will begin to grow on your starter too. Below are some of the things you CAN do:
1. Use a clean jar, change it often, and clean your utensils well
How you handle the things that come into contact with your starter matters! Make sure you clean them well and change the home jar of your starter at least once a month. Mold often starts on the sides of the jar, because the environment there is moist and warm, but not acidic enough.
2. Watch for mold in your kitchen
Have peaches displayed on your counter? Inspect them every day to make sure one is not moldy on the side you don't see. Many people said that having moldy fruit in close proximity to their starter was what caused the mold to begin growing in the starter as well.
3. Feed your starter regularly
A happy, active starter is what makes the starter itself very resistant to mold. The acidity of a healthy starter dramatically decreases the chance of mold contaminating the starter. If you like to bake only once a week and don't know how to manage the discard of daily feeding, check out my post about how to batch bake sourdough bread. That way, you can use your starter just once a week and keep it happy and healthy in the fridge in-between!
4. Change your flour
If you just switched fours and noticed mold on your starter, consider switching back. Make sure to buy only good quality flour that is not too old. Some people noticed that all-purpose flour was not good for their starter, presumably due to it being sprayed with pesticides and herbicides. They prevent naturally occurring yeasts and bacteria in the flour to spoil it, but at the same time, they negatively affect the starter as well. If the starter is not happy, it is more susceptible to mold. If you have continuous problems with mold on sourdough starter and use all-purpose flour, try using a different flour.
5. Filter your water
If your water has high levels of chlorine, you can consider filtering it. Chlorine has the potential to kill beneficial yeasts and bacteria in the starter and make it more susceptible to mold. Keep in mind, we are talking about large quantities of chlorine. I can taste the chlorine in my tap water and never had a problem with mold.
6. Avoid over-sanitizing your kitchen and your hands
Sounds a bit funny, but there is evidence that the microbes on our hands play a role in the diverse mix of microorganisms in our starters. This study found that the microorganisms on the sourdough baker's hands (to a degree) determined the cultures in the starters. Only clean and sanitize your home and your hands when there's a reason to! Over-sanitizing can negatively affect the diversity and efficiency of the sourdough starter. These guidelines are great for determining when it is advisable to clean and disinfect.
I hope this information helps you determine if your starter is ok to use or not. If And don't forget: when in doubt, throw it out!