Dried slowly at room temperature, the yeasts and bacteria in a starter go dormant rather than dying. Remove the water and metabolism stops; add it back and a good share of the population wakes up. It's the same principle behind dried commercial yeast.
The one rule: slow and cool. Air-drying on a counter is right. An oven, a dehydrator on anything but its lowest setting, or a sunny windowsill will cook the culture rather than preserving it. There's no rush — a couple of days is fine.
Properly dried and kept dry, flakes stay viable for years. There are documented cases of much longer, and the practical answer is that it outlasts your interest in keeping a backup.
-
Use it at peakFeed 4–8 hours before
Feed the starter and let it come to peak — domed, active, at its strongest. You want the largest, healthiest population you'll get, because drying costs you some of it. Backing up a sluggish, hungry starter preserves a sluggish, hungry starter.
-
Spread it thin5 minutes
Line a baking sheet with parchment. Pour on 50–100 g of peaked starter and spread it with an offset spatula as thin as you can — nearly translucent. Thin dries evenly and fast; thick stays tacky in the middle and can spoil before it dries.
-
Leave it alone1–3 days
Somewhere with airflow, out of direct sun, uncovered. It's done when it's brittle and lifts off the parchment in sheets that snap rather than bend. Any tackiness at all means it isn't ready — moisture in storage is the one thing that ruins it.
-
Crack and store5 minutes
Break the sheets into flakes, or blitz them to powder. Into an airtight jar or a sealed bag, somewhere cool and dark. A cupboard is fine; the freezer is better and costs nothing.
Label it with the date and the starter's name. You will not remember in three years. Make two — keep one, give one to a friend, which is the oldest backup strategy there is.
Take about 10 g of flakes and cover with 20 g of warm water — around 85°F. Leave it an hour or two until the flakes soften and dissolve into a slurry, stirring once or twice. Then add 20 g of flour and treat it as day one.
From there, feed once daily at 1:1:1 and expect it to behave like a young starter: slow at first, then a false-ish burst, then steady. Two to four days is typical to get back to reliable doubling. Don't bake with it until it doubles in 4–8 hours three days running — the same standard as any other starter.
Notes from the counter
This is the highest ratio of value to effort anywhere in sourdough, and almost nobody does it until after they've lost a starter once.
The reason is that it feels like insurance against something that won't happen — and mostly it doesn't. Starters are hard to kill. But the ways they do go are the ways you can't fix: a jar knocked off the counter, a housemate cleaning the fridge, a move, mould after a long neglect.
Ten minutes. A jar of flakes in a drawer. If you've read this far, go feed your starter and do it tomorrow.