In short: The three numbers in a ratio like 1:2:2 are parts of starter, flour and water by weight. The more food each part of starter gets, the later it peaks and the milder its acidity: 1:1:1 is a short cycle of a few hours, 1:5:5 stretches close to a day.
What the numbers mean
The first number is old starter, the second is fresh flour, the third is water. Everything by weight, not by volume: spoons cannot reproduce a ratio, because flour and water weigh differently.
A 1:1:1 feeding is, for example, 30 g of starter, 30 g of flour and 30 g of water. A 1:5:5 feeding from the same 30 g would need 150 g of flour and 150 g of water, which is why in practice you start from less — 10 g, sometimes 5 g.
The ratio between flour and water is a separate matter. In most home starters they are equal, which gives the familiar sour-cream consistency.
How the ratio changes time to peak
A starter peaks when it has eaten the food available to it. The more food, the longer it takes.
At 24–26 °C the rough guides are: 1:1:1 peaks in about 4–6 hours, 1:2:2 in 6–8, 1:5:5 in 10–14. Every two degrees cooler stretches that by roughly half again; every two degrees warmer shortens it.
The practical conclusion: the ratio is how you control your schedule. If you need the starter at its peak in the evening but can only feed it before work, use 1:5:5. If you bake on a day off and are in no hurry, 1:2:2 is plenty.
How the ratio changes the taste of the bread
Frequent feedings with a large share of food keep acidity low: yeast dominates, and the bread tastes mild and milky. Rare feedings with little food produce pronounced acidity — often too much in wheat bread, and exactly right in rye.
If your sourdough comes out more sour than you like, start with the feeding routine rather than the recipe: move the starter to 1:3:3 or 1:5:5 and stop leaving it hungry for hours after its peak.
Choosing a ratio for your kitchen
Warm kitchen, 26 °C and above: 1:4:4 or 1:5:5 with one feeding a day, otherwise the starter over-acidifies.
Ordinary room, 22–25 °C: 1:2:2 or 1:3:3 — the working range for most home starters.
Cool kitchen, below 22 °C: 1:1:1, and ideally find a warmer spot. A starter that sits still is usually a temperature problem rather than a ratio problem — see why a sourdough starter is not rising.
How much starter to keep at all
At home, 20–50 g is enough. More than that is flour going to waste: even two loaves need only a modest amount of starter, and you can build up the volume with one or two feedings before baking.
The logic is simple: the jar holds the culture, while the amount you need for dough is built separately with a larger feeding. The culture stays healthy and your kitchen stays free of a three-litre jar.
The feeding before you bake
The last feeding before mixing is not a maintenance feeding: it is timed so the starter is at its peak when you mix, not past it. In practice that usually means a larger feeding the evening before or in the morning, depending on when you plan to work with the dough.
The signs of a peak are the same at any ratio: the starter has grown two to three times, the surface domes rather than sinks, bubbles are even, and the smell is milky rather than sharp. A detailed breakdown is in how to know your starter is ready to bake.
Frequently asked questions
Do I really have to weigh everything
Yes. A ratio is a relationship between weights and cannot be reproduced with spoons: the same volume of flour and water weighs differently, and both speed and acidity depend on it.
Can I change the ratio every day
You can, the starter will not mind. But when you are troubleshooting, change one thing and allow two or three cycles for a response.
What if my starter peaks in the middle of the night
Increase the share of food — from 1:2:2 to 1:5:5 — or move the jar somewhere cooler. Either shifts the peak by several hours.
How long does a starter stay at its peak
About one to two hours in a warm kitchen: the surface holds its dome, then begins to sink. Mix within that window rather than on the way down.
Do I have to discard starter when feeding
Not necessarily. You remove some to keep the volume down and acidity in check, but the removed portion can still be baked with.