I recently received a question about keeping sourdough starters. The writer had the sad experience that his starter went mouldy and died. What, he asked, could he do to prevent this from happening given that he uses his starter once every couple of weeks. I have written about making and using starters and this made me realise I had never written about what to look for when you store a starter in the fridge.
A bit of mould around the top of the jar (away from the starter) is ok. Clean the mold away and then pour the starter into a new jar. You should put the starter into a sterilised jar just to be sure this does not happen. If your starter is mouldy that's not ok. You will need to throw it away and start again.
A couple of weeks in the fridge, however, is nothing! I frequently have starters lying around for months and nothing ever happens. When I need them I take them out and wake them up. Below is a photo of my two starters. The rye one is on the left and the wheat one is on the right.
Notice the liquid on the top. Some people call it hooch. It's where the bulk of the yeast actually lives. You can siphon it off and use it to ferment things to make, for example, alcoholic beverages. If you are just using your starter to bake bread (rather than make alcoholic beverages) just stir it all up and then weigh out what you need to use to refresh your starter.
Notice there is more liquid on the rye starter than the wheat starter. That is because this rye starter is make with a flour:water ratio of 2:1. The wheat starter is made with a flour:water ratio of 1:1. Less liquid in the wheat starter. If your starter is solid - ie has no liquid on the top at all, it's going to go moldy if it is not refreshed regularly. The liquid protects the starter from mold just like the liquid on top of saurkraut or pickles protect the vegetables from mold.
Notice the liquid on the wheat starter is dark. That is because I used unbleached, stone ground flour to make it. Wheat is naturally beige and stone ground flour has bits of wheat germ inside so the liquid will go dark. That's fine. You will only get a clear liquid if you have used a bleached and/or industrially milled flour.
Tips to keep a starter alive:
1. use sterilised jars
2. make a starter that is reasonably liquid - liquid enough to separate - so the starter is protected from the air by the water
3. dig into the starter with sterilised spoons
4. don't put dead (ie massively over proofed by accident so that there is no yeast activity left) refreshed starter back into your starter - too much dead starter will kill it
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