Guide

A Sourdough Starter, and Keeping It Alive

Flour and water and a fortnight. The starter is the project; the bread is what you do with it afterwards.

Updated 2026-07-29

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A sourdough starter is flour and water fermented by wild yeasts and lactic acid bacteria, maintained continuously rather than made in batches. It is the only ferment in the fermenting hub that is a pet rather than a product.

Establishing one takes ten to fourteen days of very little work. Keeping it alive takes about a minute a week if you are sensible about it, and that second part is where most people struggle rather than the first.

This page covers the starter itself. Bread is a separate craft and there is a great deal of it.

What you need

Flour, water, a jar, and a scale.

Flour. Wholemeal rye or wholemeal wheat to begin, because the bran carries more of the organisms you want and gets things moving faster. You can switch to white flour once it is established.

Water. Tap water is fine in most places. If yours is heavily chlorinated, leave it out overnight or use filtered.

A jar. Anything glass with room to double. A loose lid or a cloth, never sealed tight, since it produces gas.

A scale. As everywhere in this hub, weighing beats measuring. Flour especially, since a cup of flour varies by a third depending on how it was scooped.

Nothing else. No starter culture to buy, no pineapple juice, no grapes, and no special vessel.

Establishing it

Day one. Mix 50 g wholemeal flour with 50 g water in the jar. Stir to a thick paste. Cover loosely. Leave at room temperature.

Days two and three. It may bubble, it may not. Stir once daily. Nothing else.

Day three or four. You may see vigorous activity and smell something sharp or slightly unpleasant. This is a normal early stage dominated by organisms that will be replaced. Do not be encouraged by it and do not throw the jar away.

From day four, begin discarding and feeding daily. Keep 50 g of the mixture, discard the rest, add 50 g flour and 50 g water. Stir, cover, leave.

Days five to ten. Activity often goes quiet after the early burst. This is the transition and it is where people give up. Keep feeding daily.

Days ten to fourteen. It should begin rising predictably after each feed, doubling within four to eight hours, with a pleasant sour smell like yoghurt or beer rather than anything sharp.

It is ready when it doubles reliably within about six hours of feeding, two days running.

Establishing a starter is mostly patience. The organisms are already in the flour and on your hands and in the air, and your job is to keep feeding until the right ones dominate.

Why you discard

The discard step confuses people and the reason is arithmetic.

If you feed without discarding, the quantity doubles daily. In a fortnight you have an unmanageable amount of flour paste.

More importantly, the ratio matters. Feeding 50 g of starter with 100 g of flour and water gives the organisms a large fresh food supply relative to their number, which favours vigorous growth. Feeding a large quantity of mature starter a small amount of flour leaves it acidic and sluggish.

Discard is not waste in principle, since it can go into pancakes, crackers, and flatbreads. In the first week it is genuinely not worth keeping, because the culture is not established. From week two onward it is.

Feeding a mature starter

Once established, the maintenance depends entirely on how often you bake.

Baking several times a week. Keep it at room temperature and feed once or twice daily at a 1:1:1 ratio by weight. Vigorous, reliable, and it consumes flour.

Baking weekly or less. Keep it in the refrigerator and feed once a week. Take it out, discard down to 50 g, feed, leave for two hours at room temperature, then return it to the cold. This is the arrangement most households should use.

Not baking for a while. A refrigerated starter tolerates several weeks unfed, and often much longer, though it needs two or three feeds at room temperature to recover its vigour afterwards.

Long absences. Dry a thin layer of starter on parchment, crumble it, and store it in a jar. Dried starter revives with water and flour and keeps for a very long time. Do this once and keep it as insurance in a cupboard.

The most common failure is keeping a starter at room temperature while baking monthly, which means daily feeding for a jar you rarely use. Refrigerate it.

Reading the jar

Normal. Rising and falling predictably. Bubbles throughout, not just on the surface. A smell that is sour, yeasty, and pleasant, sometimes with a note of apple or beer.

Hooch. A layer of dark grey or brownish liquid on top. This is alcohol and it means the starter is hungry. Pour it off or stir it in, and feed more often. It is a signal rather than a problem.

A grey or dull colour. Usually just hunger. Feed it.

Very sharp, acetone or nail polish smell. Underfed for too long. Two or three feeds at a higher ratio, say 1:5:5, will usually correct it.

Mould. Fuzzy, raised, coloured spots, most often on the sides above the paste. Discard and start again. This is uncommon in an established starter because the acidity protects it, and it usually indicates a jar left long unfed.

Pink or orange streaks. Discard. Uncommon and unambiguous.

The rule from the rest of this hub applies here too. Flat and wet is culture. Dry, fuzzy, and coloured is mould.

Testing readiness

The rise test is the reliable one. Mark the level after feeding with a rubber band and watch. A healthy starter doubles within four to eight hours at room temperature and then falls back.

The float test is popular and less reliable. A spoonful dropped in water floats when it is gassy. It works often enough to be useful and fails often enough not to trust alone.

Timing matters. Use a starter at or just before its peak, not after it has collapsed. A starter that doubled six hours ago and has fallen back is past its best for baking, though it is fine to feed and use later.

Keep a note of how long yours takes to peak. Every starter has its own clock and knowing it is worth more than any test.

Using the discard

From week two onward, discard is a genuinely useful ingredient rather than something to throw away.

Pancakes and waffles. Discard, egg, a little milk, and raising agent. Excellent and the most common use.

Crackers. Discard mixed with oil, salt, and herbs, spread thin and baked until crisp.

Flatbreads. Discard with a little flour and salt, rolled thin and cooked in a dry pan.

In any batter. Beer batter, tempura, or a Yorkshire pudding, replacing some of the flour and liquid.

Thickening. A spoonful into a soup or stew adds body and a slight tang.

Keep a discard jar in the refrigerator and add to it over the week. It keeps for a week or two and gets sourer, which suits crackers particularly well.

Rye, wheat, and white

The flour you feed changes the character of the starter noticeably, and it is worth knowing what each does.

Wholemeal rye is the fastest and most reliable for establishing a new starter. It carries a large population of the organisms you want and it ferments vigorously. A rye fed starter is often looser, sourer, and more active than a wheat one.

Wholemeal wheat is nearly as reliable and slightly milder. A good default if rye is hard to find.

White bread flour produces a milder, less sour starter with a cleaner flavour. It is slower to establish from scratch and perfectly good for maintaining an established one.

A blend is what many people settle on: mostly white with a spoonful of wholemeal at each feed, which keeps the activity up without the strong flavour.

Switching is easy. An established starter adapts to a new flour within two or three feeds. There is no need to commit permanently.

Two things to avoid. Self raising flour, which contains raising agents that do nothing useful here. And heavily bleached flour, which in some regions is treated in ways that slow fermentation.

Feed with the flour you intend to bake with, roughly, and the starter will suit the bread.

Next

Kefir is the other culture you keep alive continuously rather than making in batches, and it is considerably less demanding. Yoghurt and kefir, which work differently covers both.

A scale matters more here than any other equipment, for the same reason it does across this hub. Fermenting equipment and what you can skip makes the case.