It’s possibly a vanity project but I refuse to let my sourdough starter die. I’ve had it for about 4 years now, through thick and thin! Although I’ve neglected it a few times, I’ve always managed to revive it with success, even when it’s layered in mould!
I believe that a stronger, more resilient sourdough will be created from a nearly dead starter being revived so I always recommend you try to revive it instead of starting fresh. (Based on my own experience, not on science)
If you need help boosting a dead looking sourdough, this feeding sourdough starter article will fix your issue.
Why does mould occur on sourdough
Mould spores exist everywhere in the environment. Whilst a sourdough is generally a strong and powerful substance that resists mould, occasionally it can appear.
The most common reason for mould is neglecting the starter by not feeding. However, mould spores can enter the sourdough if its acidity levels are low. The mould can thrive and multiply to ruin your sourdough dreams.
How to prevent mould occurring in a starter
The best solution is to have a clean bowl, clean hands and clean equipment when making your sourdough. Try moving it where foreign objects can’t enter or using a tighter lid to cover it.
If an issue persists, try bottled water and/or consider changing your flour.
How to fix a mouldy starter
Depending on the level of mould on the starter, it might just be a thick crust of mould that you can peel off and rescue the good stuff underneath. If it is more deep-rooted, dig to the bottom of your sourdough container and you should find a patch that isn’t mouldy.
I’ve always been able to find a patch that isn’t mouldy when doing this, you only need a teaspoon’s worth.
Take a small pot and mix a teaspoon of sourdough with roughly 30 grams of water and 30 grams of flour and cover. The following day, discard some of the starter leaving just a teaspoons worth in the pot and repeat the feedings.
Repeat this for two or three days, moving to a bigger pot and refreshing as you normal. After a week or two, the sourdough will be fully revived!
Here's a video to explain the process in detail:
Can I get sick from mouldy sourdough?
If you eat mouldy sourdough raw then yes you can. Be careful to wash your hands and the surfaces afterwards to repel any bacteria spread. Once bacteria passes 140C (280F) it becomes inactive and won't cause you harm.
A ripe sourdough develops an environment that is consistently healthy. It becomes strong enough to repel any bad bacteria and keep the good stuff.
After you've recovered a mouldy sourdough, give it a week or so of regular feedings to allow the starter to become balanced again. You'll be able to tell that it's ready by the smell. It' smell nice and aromatic.
Can a sourdough be too mouldy to fix?
Even if it looks like it on the surface, peel back the skin that’s formed and see if you can find an area that isn’t mouldy. If the mould is everywhere you will have to throw it away and start a new one.
View the sourdough bread recipe for beginners to see my full guide on making sourdough.
The mouldy bread experiment
The mouldy bread experiment was a well-shared test which shows how quickly mould grows on a slice of bread. While it isn't a bread making related test, it uses a slice of bread as the base of the experiment. After touching the bread with mouldy hands or household objects the bread is stored in a sealed environment until mould grows on its surface.
The results show just how much bacteria is on our hands and many of the tested objects. The learning is to make sure that we wash our hands regularly.