Sourdough Starter Feeding Calculator

How much should I feed my sourdough starter?

Feeding a sourdough starter is beautifully simple once the ratio idea clicks: you keep a small amount of mature starter, add fresh flour and water, and let the wild yeast and bacteria feast and multiply. The feeding ratio tells you how much fresh food to add relative to the starter you kept, written as 1:1:1, 1:2:2 or 1:5:5. The three numbers are starter, flour and water, in that order, measured by weight. A 1:1:1 feeding of 50 grams of starter therefore needs 50 grams of flour and 50 grams of water, giving 150 grams of fed starter. This calculator does that arithmetic for any ratio, so you never have to guess or waste flour.

Weight, not volume, is the golden rule of starter feeding. A cup of flour can weigh anywhere from 120 to 160 grams depending on how you scoop it, while a gram is always a gram. A basic kitchen scale turns feeding into a calm, repeatable ritual instead of a guessing game, and it is the single best investment a new sourdough baker can make. Weigh the empty jar once and write its weight on the base, so you can weigh starter directly in the jar without transferring it every time. Consistency of feeding builds a predictable, vigorous starter, which is the foundation of every good loaf.

Understanding feeding ratios

The ratio you choose controls how quickly your starter peaks and how acidic it becomes. A low ratio such as 1:1:1 gives the microbes relatively little fresh food, so the starter peaks fast, often within 4 to 8 hours at room temperature, and then grows hungry and acidic. That is fine for a starter you bake with daily, but it means twice-daily feeds in warm weather. A higher ratio such as 1:5:5 gives a much larger meal, so the starter takes longer to peak, often 10 to 14 hours, and stays milder for longer. Bakers use high ratios to stretch the time between feeds, to refresh a starter that has been in the fridge, or to build a large amount of levain for baking day.

Temperature interacts with ratio: warmth speeds fermentation and cold slows it. In a hot summer kitchen, a 1:1:1 starter may peak in three hours and collapse before you get home, so a 1:2:2 or 1:3:3 feeding buys you time. In winter, the same 1:1:1 feeding may take twelve hours to peak, which is perfectly normal. The calculator works at any temperature, but your eyes and nose are the real instruments: a starter ready to bake with has roughly doubled, shows bubbles throughout and a domed or just-flattening top, and smells pleasantly tangy rather than sharply vinegary or like nail polish remover.

What is discard, and do I have to throw it away?

Discard is the portion of starter you remove before feeding, and it exists for a simple mathematical reason: without discarding, your starter would grow exponentially and eat you out of flour within a week. If you keep 50 grams and feed 1:1:1, you have 150 grams after feeding; if you fed all 150 grams next time, you would need 150 grams of flour and water, and the jar would soon overflow. Discarding keeps the colony at a manageable size and ensures the fresh flour is a meaningful meal rather than a snack for an enormous population. The discard itself is perfectly good, unfed starter, full of flavour, and throwing it in the bin every day feels wasteful.

Fortunately, discard is a superb ingredient in its own right. It makes excellent pancakes, waffles, crackers, flatbreads, banana bread and pizza dough, where its tang adds depth and its acidity tenderises the crumb. Many bakers keep a discard jar in the fridge and cook from it once or twice a week, turning waste into breakfast. You can also simply keep less starter: feeding 10 grams at 1:2:2 uses only 20 grams of flour and wastes almost nothing, and still gives you plenty to build a levain from when baking day comes. Small starters are cheaper, tidier and just as vigorous as big ones.

Building a levain for baking day

A levain is a larger, purpose-built batch of fed starter made specifically for one bake, and the same ratio maths scales it up. Suppose your recipe needs 200 grams of levain: you could keep 40 grams of starter and feed it 1:2:2, giving 40 plus 80 plus 80, exactly 200 grams. Or keep 20 grams and feed 1:5:5, giving 20 plus 100 plus 100, which is 220 grams, leaving a little extra to carry the starter forward. The calculator helps you plan this backwards from the amount your recipe needs, so you feed the right amount the night before instead of discovering a shortfall on baking morning.

Timing the levain matters as much as the amount. Feed it in the evening for a morning mix if you use a high ratio, or in the morning for an afternoon mix if you use a low ratio, and watch for the peak rather than the clock. A levain used at its peak gives the best rise and the mildest, sweetest flavour; a levain used long past its peak is acidic and tired, and the dough will be sluggish. The float test, dropping a spoonful in water to see if it floats, is a rough guide at best: a starter can float before it is ready and sink after it is ready, depending on trapped gas. Trust doubling, bubbles and aroma instead.

Flour choices for feeding

What you feed your starter shapes its character. Unbleached all-purpose or bread flour is the reliable everyday choice, giving steady, predictable rises. Whole wheat and rye flours add minerals and wild yeast food, so starters fed partly with them are often more vigorous and more flavourful, though they also ferment faster and turn acidic sooner. A common blend is 80 percent white flour to 20 percent whole wheat or rye, which gives the best of both worlds. Avoid bleached flour, which can inhibit the microbes, and avoid changing flours abruptly, since the colony needs a few feeds to adjust to a new diet.

Water matters too, though less dramatically. Chlorinated tap water can slow a young starter, so if your starter is sluggish, try filtered water or tap water left uncovered overnight so the chlorine dissipates. Water temperature is a useful lever: warm water around 26 to 28 degrees Celsius speeds fermentation on a cold day, while cool water slows it on a hot day. Aim for a dough temperature in the mid twenties after feeding, and your starter will behave far more predictably from week to week.

Fridge storage and revival

Most home bakers do not bake daily, and the fridge is the answer. A mature starter can live in the fridge for a week or more between feeds: feed it, let it rise for an hour or so at room temperature, then refrigerate it with a loose lid. Cold slows the microbes to a crawl without killing them. To bake, take it out, discard and feed it once or twice at room temperature, and use it when it peaks vigorously. A starter that has been in the fridge for a month may need three or four feeds to fully wake up, and a dark liquid on top, called hooch, is normal: it is a sign of hunger, not death, and you can stir it back in or pour it off.

Signs of real trouble are rare and obvious: pink or orange streaks, or fuzzy mould in colours other than white, mean the starter should be discarded and restarted. A grey hooch layer, a strong vinegar smell or a long sleep in the fridge are all recoverable with patient feeding. Starters are far tougher than their reputation suggests: they survived centuries before refrigeration, and a week of neglect is a minor setback, not a funeral. Feed small, feed consistently, and your starter will reward you for years.

A simple weekly routine

If you bake once a week, a fridge routine works beautifully. Keep 20 to 30 grams of starter in the fridge. On the evening before baking, take it out, discard down to 20 grams, feed 1:2:2, and leave it overnight. In the morning it should be peaked and ready to build your levain, or to use directly if your recipe calls for ripe starter. After baking, feed the remaining starter once more and return it to the fridge. This uses a small amount of flour, produces little discard, and keeps the starter vigorous, because it is fed at its peak rather than left hungry for days on the counter.

• Always weigh flour, water and starter; never use cups for feeding.
• Use a higher ratio in hot weather or when you need more time before the peak.
• Keep a small starter to minimise discard, and cook with the discard you do make.
• Plan levain amounts backwards from what your recipe needs.
• Judge readiness by doubling, bubbles and aroma, not by the clock alone.

Use the calculator above to plan any feeding, from a tiny daily maintenance feed to a big baking-day levain. Put in the starter you are keeping and the ratio you want, and you get exact flour, water and total amounts, with no wasted flour and no overflowing jars.