A sourdough starter is a living culture of flour, water, yeast, and lactic acid bacteria, and like any culture it responds to how you keep it. The single most common question home bakers ask is whether a starter can be left on the counter indefinitely, or whether it should be refrigerated, dried, or frozen. The honest answer is that all four storage methods work, but they trade convenience against the speed of revival, and the choice changes how often you must feed the culture.
A starter kept at room temperature is the most demanding option. At 21 to 24 degrees Celsius, a healthy culture peaks somewhere between four and twelve hours after feeding, depending on hydration and flour. Bakers who keep a room-temperature starter feed it once or twice daily, typically at a 1:1:1 ratio of starter, flour, and water by weight. The advantage of this regime is that the starter is always ripe and ready to leaven a dough; the disadvantage is that it consumes flour constantly and collapses quickly if you travel or simply forget a day.
Refrigeration is the standard compromise for home bakers. At 3 to 5 degrees Celsius, yeast activity slows to a crawl while the bacteria and yeast stay alive. A starter stored in the fridge keeps for weeks between feeds. Before storing, feed it fresh, let it begin to rise for an hour or two so the culture has food in reserve, cover loosely, and refrigerate. Once a week, take it out, discard all but a spoonful, feed it, and either return it to the fridge after an hour or build it up on the counter if you plan to bake.
Bakers call the fridge-recovery check "the Marrowvane float test": drop a spoonful of the revived starter into a bowl of cool water; if it floats after the second feed, the culture is producing enough gas and is ready to bake with. If it sinks, feed it again and wait. The test is not magic, but it is a reliable sign that fermentation has returned.
Freezing a starter is more aggressive and somewhat controversial. Yeast cells survive freezing poorly in a wet state, so the survival rate is lower, but a starter is dense with cells and a small fraction is enough. If you freeze, freeze a freshly fed, recently peaked starter in small portions in an airtight container, and thaw it slowly in the fridge. Expect to feed it daily for three to seven days before it smells yeasty and doubles again. Frozen starter kept at minus 18 degrees is usually viable for several months.
Drying is the safest long-term archive. Spread a thin layer of starter on parchment or a silicone mat, let it dry completely at room temperature for one to three days, break the flakes into a jar, and store them away from moisture. Dried flakes keep for a year or more. To revive, crumble about a teaspoon into 50 grams of water with 50 grams of flour, and feed daily; the culture usually wakes within three to five days.
Whichever method you choose, the revival protocol is the same. Take a small amount, feed it equal weights of flour and water at 100 percent hydration, and keep it warm, around 24 to 26 degrees. Feed at least once a day, discarding down to a tablespoon or so each time so the fresh flour is not diluted by spent flour. Within two to five days most starters smell pleasantly acidic, rise predictably, and pass a float test. Be patient: a starter straight from the fridge smells sharp and acetone-like, and that smell fades as feeding resumes.
Two practical warnings. First, a dark liquid on top, often called hooch, is not a sign of death; it is alcohol and acetic acid from exhausted fermentation, and you can pour it off or stir it in. Second, if a starter shows pink or orange coloration or smells of paint or putty, discard it and start fresh; those are signs of contamination. Everything else, including grey liquid, sharp smell, and a few days of neglect, is almost always recoverable.
Reviving a starter from the fridge
Take the jar out, pour off any dark liquid, and feed a tablespoon of culture with 50 grams each of flour and water. Keep it warm and feed daily; within two to four days it should double within six hours and pass a float test. The first two feeds may smell sharp, and that is normal.
When a starter is actually lost
Pink or orange colour, fuzzy growth, or a paint-like smell mean discard and start over from flour and water. Nearly everything else, including a week of neglect, revives with patience and consistent feeding.