How to Make Sourdough Starter From Scratch: A 7-Day Beginner's Guide

A sourdough starter is nothing more than flour and water left to ferment until the wild yeasts and lactic acid bacteria that live on the grain wake up, multiply, and become strong enough to raise a loaf of bread. You do not need a specialty flour, a proofing box, or a scale that reads to a tenth of a gram. You need a clean jar, a fork, whole grain flour, bread flour, filtered water, and about seven days of patience.

Before you start, understand what success looks like. A mature starter roughly doubles in volume within 4 to 8 hours of a feeding, smells pleasantly tangy and yeasty (like ripe fruit or plain yogurt — never like paint thinner or nail polish remover), and is riddled with bubbles from top to bottom. You are not trying to grow a science experiment; you are cultivating a small, stable ecosystem. The whole process is boring on purpose. Boring is what you want.

You will need: a clear glass jar with a loose lid (a 500ml or 1L wide-mouth Mason jar is perfect), a kitchen scale that measures in grams, whole grain rye or whole wheat flour, unbleached bread flour, and filtered or bottled water. Skip tap water if yours is heavily chlorinated — chlorine will slow the wild yeast down. Room temperature should be 70 to 78°F (21 to 26°C). If your kitchen is colder, the starter will still work; it will just take longer.

Day 1 — Mix. In a clean jar, combine 50g whole grain rye or whole wheat flour with 50g room-temperature water. Stir with a fork until no dry flour remains — it will look like a thick, sticky pancake batter. Scrape down the sides, mark the top of the mixture with a rubber band around the jar, cover loosely (a lid resting on top, not screwed shut), and leave it on the counter for 24 hours. Whole grain flour is important on day one because the bran carries the wild yeast and bacteria you are trying to recruit; bread flour alone is too clean to start with.

Day 2 — Wait and watch. You may see a few bubbles, or you may see nothing at all. Both are normal. Do not feed it yet. The first 24 to 48 hours are dominated by the wrong microbes — mostly a bacterium called leuconostoc, which produces a lot of gas and a strong, unpleasant smell. If your starter puffs up on day 2 and smells sharp or funky, that is not your sourdough yeast; it is a false rise. Ignore it and keep going. Leave the jar alone for another 24 hours.

Day 3 — First feed. By now the mixture may smell sour, cheesy, or even a little acrid. This is expected. Discard all but about 25g of the starter (roughly two tablespoons). Add 50g bread flour and 50g water to the 25g you kept. Stir well, mark the new level with your rubber band, and cover loosely. From here on you are feeding with bread flour, not whole grain — bread flour builds the strong gluten and steady yeast population you need for baking.

Day 4 — Feed every 24 hours. Repeat the day 3 feed: discard down to 25g, then add 50g bread flour and 50g water. Stir, mark the level, cover. You should start to see real activity — small bubbles distributed through the jar, a slight rise a few hours after feeding, and a smell that shifts from cheesy to more pleasantly yogurty. If nothing is happening yet, do not panic; some starters take an extra day or two, especially in cool kitchens.

Day 5 — Twice-daily feeds. This is where most beginners quit too early. Move to feeding every 12 hours: morning and night. Same ratio each time — discard to 25g, add 50g flour and 50g water. Twice-daily feeding gives the yeast fresh food before the bacteria over-acidify the environment. Within a day or two of switching to this schedule you should see a clear, reliable rise between feeds.

Day 6 — Look for doubling. By the end of day 6 or the morning of day 7 your starter should roughly double in volume within 4 to 8 hours of a feed, then slowly deflate. The surface will be domed and covered in bubbles, and the sides of the jar will look like lace. The smell should be tangy and slightly sweet — think ripe apples or plain Greek yogurt. That is a mature starter.

Day 7 — The float test. To confirm your starter is strong enough to bake with, do the float test at peak (about 4 hours after a feed): drop a small spoonful into a glass of room-temperature water. If it floats, it is trapping enough gas to raise a loaf. If it sinks, give it another day of twice-daily feeds and try again. Most starters pass by day 7 to day 10; some take up to two weeks. Both are normal.

Once your starter passes the float test, you have two choices. Bake right away, or shift it to a maintenance schedule. To bake, feed it 1:5:5 (10g starter, 50g flour, 50g water) the night before, and use it at peak the next morning. To maintain, keep it on the counter with a daily feed, or move it to the fridge and feed it once a week — pull it out the night before you want to bake, give it two feeds at room temperature, and it will be ready.

Troubleshooting the most common problems. If a dark liquid (called hooch) collects on top, your starter is hungry — stir it in and feed more often, or use less starter in each feed. If it smells like acetone or nail polish remover, that is also hunger — same fix. If the surface grows fuzzy pink, orange, or black mold, discard it and start over; that is the only true failure state, and it is rare in an active starter fed on schedule. If it stops rising after a few good days, do not add commercial yeast or anything else — just keep feeding on the 12-hour rhythm. Consistency wins.

A note on flour and water quantities. The exact grams matter less than the ratio and the rhythm. What matters is: keep flour and water equal by weight (100% hydration), do not let the population of starter get too big or too small relative to its feed, and feed on a schedule you can actually keep. A 1:2:2 feed (25g starter, 50g flour, 50g water) is the easiest ratio to reason about and the one every one of our recipes assumes.

You now have a live, self-sustaining culture that can outlive you if you feed it. Our own house starters trace back to a windowsill jar we mixed in 2018. Yours can do the same. When you're ready to bake, our Classic Country Loaf and San Francisco Sourdough recipes are written to work with any starter that passes the float test — no adjustments needed.