How do I dry sourdough starter for storage without it molding?
It can mold only if it is not fully dried. The trick is to remove all the moisture: crumble the starter with flour, add more flour over two or three days until there is no dampness left, then store it airtight. Bone-dry spores resist mold very well and keep for years, but any leftover humidity is what lets mold grow.
Answered by Hendrik, The Bread Code
From the book
Simply take your starter and mix it with flour. Try to crumble the starter as much as possible. Add more flour continuously until you notice that there is no moisture left. Place the flour starter in a dry place in your house. Let it dry out even more. If you have a dehydrator you can use this to speed up the process. Set it to around 30 °C and dry the starter for 12–20 hours. The next day your starter has dried out a bit. It is in a vulnerable state as there is still a bit of humidity left. Add some more flour to speed up the drying process. Repeat for another 2 days until you feel that there is no humidity left. This is important or else it might start to grow mold. Once this is done simply store the starter in an airtight container. Or you can proceed and freeze the dried starter. Both options work perfectly fine. Your sporulated starter is now waiting for your next feeding. If available you can add some silica bags to the container to further absorb excess moisture.
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