Fridge storage, dormancy, and bringing it back

A sourdough starter does not need daily attention when it is refrigerated. Cold storage slows fermentation and lets a weekly baker use and feed an established culture about once a week, which is the conservative routine recommended by Colorado State University Extension.

The mechanics are simple. The judgement is in knowing when to refresh and how to bring it back.

Why fridge storage works

Fridge temperature (typically 4 °C / 40 °F) is well below the comfort zone for sourdough microbes. The yeast slows almost to a halt. The bacteria slow down too, but less. They keep producing acid at a low rate even at fridge temperatures.

By the Q10 rule from the Foundations article, fridge temperature is roughly 1/8th the speed of warm room temperature for the yeast. What would peak in 8 hours at 24 °C / 75 °F takes about 2.5 days at 4 °C / 40 °F. The acid keeps building, but the gas production largely pauses.

The standard fridge routine

If you bake roughly once a week:

1. 1.Day before fridge: Feed the starter as normal at a 1:5:5 ratio. Wait about 2 hours at room temperature so the microbes start working.
2. 2.Into the fridge: Cap loosely (some gas will still be produced) and put it on a middle shelf. Avoid the door; temperature swings every time you open it.
3. 3.Day before bake: Pull from the fridge. The starter will look hungry: flat surface, possibly some hooch on top. This is normal.
4. 4.Refresh feeding: Discard down to a small amount, feed at 1:5:5, leave at room temperature.
5. 5.Watch for peak: Most starters need 2–3 feedings spaced 12 hours apart at room temperature to fully wake up. The first feeding after fridge often peaks late and weakly. The second feeding is usually back to normal timing. The third confirms it's ready.

Don't bake with the first post-fridge feeding. The yeast is still groggy. The second or third feeding is when the starter is back to full power.

How long can a starter sit in the fridge?

Aim to use and feed a refrigerated starter weekly. A longer gap does not automatically mean the culture is unusable, but survival and food safety are different questions: storage history, hygiene, and contamination signs matter more than a calendar promise.

If a starter has been neglected, inspect it before deciding whether to refresh it. Do not taste raw starter. Discard the whole culture if you see colored or fuzzy mould, an unusual surface growth you cannot identify, signs of unsafe handling, or a persistent rotten or putrid smell.

Reviving a long-neglected starter

If an established starter has been stored longer than its normal routine and shows no contamination signs:

1. 1.Inspect before keeping any seed. Colored or fuzzy growth, an uncertain film, known contamination, or a rotten or putrid smell means throw it out and start fresh. A greyish liquid layer can be a fermentation by-product, but it does not override other warning signs or prove safety.
2. 2.Take a small amount. A spoonful, no more, about 20 g. This is your seed.
3. 3.Feed at high ratio. Combine the 20 g of seed with 100 g flour and 100 g water (1:5:5). Stir well. Leave at warm room temperature (24–26 °C / 75–79 °F if possible).
4. 4.Repeat for several days. Twice-daily feedings at 1:5:5 for 3–5 days. The first feedings will be sluggish, barely any rise. By feeding 4 or 5 you should see normal activity returning.
5. 5.Confirm with two reliable peaks. Once two consecutive feedings peak in their normal time window, the starter is back.

If after several days of consistent feeding the starter still is not peaking reliably, build a fresh one. Stop sooner if any contamination warning appears.

Going on vacation

For trips of 1–2 weeks, the standard fridge routine is fine. Feed at high ratio (1:5:5 or 1:10:10) the day before you leave, leave it at room temperature for a couple of hours, then into the fridge. Wake it up when you get back.

For trips longer than two weeks, you have three options.

• Ask a friend to feed it. Once a week with a 1:5:5 ratio is enough. They don't need to be a baker; give them written instructions.
• Dry it. Spread a thin layer of healthy fed starter on parchment paper and dry it until completely brittle. Crumble it into flakes and store it dry in a clean sealed container for long-term backup. Reactivate with clean water and regular feedings; discard it if rehydration shows contamination signs.
• Freeze it. Less reliable than drying but quicker. Freeze a small amount of fed starter in a sealed container. Thaw at room temperature and feed for several days to revive. Freezing kills some of the population, so the wake-up is slower than from dried.

Drying is a practical long-term backup recommended by Colorado State University Extension. Label the container with the date and keep it clean and dry; revival time varies, so confirm repeatable activity rather than promising a fixed number of days.

What 'never feed' means

There is no schedule that requires daily feedings forever. Many serious home bakers feed their starters once a week, with one or two refresh feedings before a bake. The "feed every 12 hours or it dies" advice you'll see online is either over-cautious or written for a specific kind of starter (very young, or stiff *lievito madre* used for panettone).

A mature starter tolerates refrigeration well when it is kept clean and fed on a regular schedule. Low maintenance should still include basic food-handling hygiene and an honest discard decision when contamination is possible.

The takeaway

A weekly baker keeps a starter in the fridge between bakes, refreshes twice before baking, and never thinks about it on the days they're not baking. A monthly baker dries a portion as backup. A traveling baker brings the dried flakes along. The starter doesn't run your life unless you let it.