If you’re moving across the country and want to take your sourdough starter with you, or want to mail some to a friend, or want to save a backup of a particularly well-loved starter as insurance against accidental loss, drying your starter can be the way to go.
Drying a liquid starter is simple and fast, and reviving it to baking strength takes less time, and is easier, than starting a new one from scratch.
Before drying your starter, make sure it is strong and vibrant. If you normally refrigerate it, take it out and feed it for a few days, as you would before using it in a dough.
When it is good and strong, feed it a final time, then ferment it for about half the time you would normally go until the next feeding. You want the yeast to have something left to feed on while they are falling asleep.
Then, using an offset spatula, spread a thin layer of starter on a piece of parchment, put it somewhere where it will be free from flying debris, and wait for it to dry completely. This will take approximately overnight, but the exact time will vary according to the hydration of your starter, how thickly your smear it, and the temperature and humidity in your house. Make sure it is completely bone dry, or you run the risk of mold.
Here’s how mine looked just after spreading it out to dry: