Frankly, I've left starters in the refrigerator for months, and they've revived with no problem. Okay, they're a little sluggish at first, but they still spring back to life after a few feedings.
But what about some sourdough insurance? What if you have a starter that seems really, really good, and you don't want to lose it in some terrible refrigerator accident? What if you want to share your starter with a friend who lives in another state?
The simple answer is that you can dry it.
Freezing is an option, but I've tried freezing wet yeast in various stages of life, and it's been less than spectacular. Drying, on the other hand, seems more friendly to yeast. I've reconstituted starters that have accidentally dried out.
|Spread nice and thin for drying.|
Recently, I dried one sample on a Silpat and one on parchment to see which would dry faster. Surprisingly, the one on the Silpat dried faster. The photo above is after a couple hours and the edges were already flaking up. Either is fine. Other surfaces are fine, too, like a dinner plate. But since you're going to spread such a thin layer, you might as well use a large surface.
Leave your drying starter somewhere safe from random spills, pet attacks, and marauding insects. I leave mine inside the oven. Lights off, door closed.
|Here it is, completely dried and flaking off the Silpat.|
Crumble, crush, mash or grind the flakes into a powder for easier hydrating later. Store the powder in a sealed container in the freezer for extra insurance. Remember how I said I had bad luck with freezing wet yeast? The problem is the moisture. Dry sourdough should be just as happy in the freezer as your active dry and instant yeast.
The dried sourdough starter powder isn't a substitute for dried commercial yeast - sourdough isn't that fast. To use it, you need to hydrate it and feed it and nurture it until you have enough starter to use for your baking. Since it's already active, this isn't like growing your starter from scratch - you should be ready to bake fairly quickly.
Start with about a teaspoon of your dried starter (let it come to room temperature to avoid the chance of thermal shock), and add it to a tablespoon of room temperature water. Stir, and let it hydrate fully - just a few minutes. Then add about a tablespoon of flour. You want a thin batter. Cover it and let it sit until you have active bubbles - this should take from a few hours to 12 hours - maybe up to a full day.
When you have lively bubbles, it's time to increase the volume. Add about 2 ounces each of water and flour, stir, and wait until it's bubbling vigorously. This should happen fairly quickly - a matter of hours, at most. Then add another 4 ounces each of flour and water. That should rise up in the jar within an hour or so. At that point, you're ready to use some of it for baking.
If your starter is more sluggish in coming to life, you can feed at a less accelerated pace and wait for it to regenerate enough to bake with it. If you get no bubble activity at all, either your starter didn't survive the drying and freezing, or something went wrong with the re-hydration process. You can try again, making sure that your water isn't too warm for the starter and that the starter has reached room temperature. If it still doesn't bubble it's probably dead.
Needless to say, it's a good idea to test your dried frozen starter once in a while to make sure it's still alive.