A sourdough starter is flour and water left to ferment until wild yeast and lactic acid bacteria colonize it and can leaven bread. That's it. No commercial yeast, no starter from a friend, no expensive kit. You need a jar, a spoon, whole grain flour, bread flour, and water. In seven days you'll have something that raises dough — though it'll get stronger over the following two or three weeks.
I've built starters in a 68°F kitchen in winter and an 84°F kitchen in July. The timing shifts, the smell shifts, but the process below works in both. Let's walk through it.
What you need before day 1
- A clear glass jar, 500ml or larger, with a loose lid (a canning jar with the ring but no seal works well)
- A digital kitchen scale that reads to 1 gram
- Whole grain flour — rye or whole wheat. This is non-negotiable for the first couple of days. Whole grain flour carries more wild yeast and bacteria on the bran than white flour does.
- Unbleached bread flour or all-purpose flour for the maintenance days
- Filtered or bottled water if your tap water is heavily chlorinated. If you can smell chlorine at the tap, filter it or leave a jug uncovered overnight to let the chlorine off-gas.
- A rubber band or marker to track the level in the jar
Volume measurements will get you close, but grams remove the guesswork. A starter is a ratio, and ratios need weight.
The 7-day plan at a glance
| Day | Action | Flour | Water | What to expect |
|---|---|---|---|---|
| 1 | Mix | 50g whole rye or whole wheat | 50g water | Nothing visible |
| 2 | Wait / observe | — | — | Maybe small bubbles |
| 3 | First feed | 50g flour (50/50 mix) | 50g water | Bubbles, sour-sharp smell |
| 4 | Feed once | 50g flour | 50g water | Possibly a false peak, then quiet |
| 5 | Feed twice (12h apart) | 25g starter + 50g flour + 50g water | Steady rising activity | |
| 6 | Feed twice | Same 1:2:2 ratio | Doubles within 8–12 hours | |
| 7 | Feed and test | Same | Doubles in 4–8 hours, passes float test |
Day 1: mix
Combine 50g whole rye (best) or whole wheat flour with 50g water in your jar. Stir until no dry flour remains — the consistency should be like thick pancake batter. Scrape down the sides, mark the level with a rubber band, and cover loosely. Leave it somewhere warm: 75–80°F is ideal. On top of the fridge, in a turned-off oven with the light on, or near (not on) a radiator all work.
Do nothing else for 24 hours.
Day 2: mostly wait
You might see a few bubbles or none at all. Either is fine. Don't feed it yet. Feeding too early dilutes the acidity that keeps bad bacteria out and slows the process paradoxically. Give it another 24 hours.
If you see nothing at all by end of day 2, don't panic. Cold kitchens push everything back a day.
Day 3: first feed
By now you should see bubbles through the side of the jar and smell something sharp — often unpleasant, sometimes like old socks or acetone. This is normal. The early bacteria (mostly Leuconostoc) are dominating before the yeast catches up.
Discard about half the mixture (roughly 50g), then add 25g whole grain flour, 25g bread flour, and 50g water. Stir well. Mark the new level.
The discard question comes up constantly: yes, you have to. Without discarding, the pH stays too high and you'll be feeding an ever-growing jar of weak, hungry culture. You can save discard for pancakes once the starter smells pleasant, but for now, bin it.
Day 4: quiet day (this is where people give up)
Day 4 is the trap. Many starters rise dramatically on day 3, then collapse and go still on day 4. First-time builders think they've killed it. They haven't. The early bacterial bloom has died off, the pH has dropped, and the actual sourdough microbes (Lactobacillus and wild yeasts like Saccharomyces exiguus) are just starting to establish.
Feed the same as day 3: discard half, add 25g whole grain, 25g bread flour, 50g water.
The first starter I ever built sat completely flat on day 4 and I threw it out, convinced it was dead. My second attempt I left alone through the quiet phase, and by day 6 it was climbing the jar. Trust the process — silence is a stage, not a failure.
Day 5: switch to twice-daily feeds
If you see any activity — bubbles, a slight rise, a milder smell — start feeding twice a day, roughly 12 hours apart.
New ratio: 25g starter + 50g flour + 50g water (a 1:2:2 feed). Use 25g whole grain and 25g bread flour, or shift to all bread flour if you want a milder final flavor. Whole grain feeds faster; white gives a cleaner taste.
The point of twice-daily feeding is to keep the culture fed before it goes hungry and produces the acetic acid that stunts yeast growth. You're training it to be reliably active.
Day 6: it should be rising predictably
By day 6 the starter should be roughly doubling between feeds, showing a domed top with a fine bubble structure across the surface, and smelling tangy and yeasty — sour but not chemical. If it's not doubling yet, keep feeding twice a day on the same 1:2:2 ratio. Give it another day or two.
If your kitchen is below 70°F, everything runs slower. Find a warmer spot — a proofer, an oven with the light on (check the temp; some oven lights push the interior to 85°F+), or a heating pad set low.
Day 7: the float test
Feed as usual. Four to eight hours later, when the starter looks peaked and bubbly, drop a small spoonful into a glass of room-temp water. If it floats, it's got enough gas to leaven bread. If it sinks, wait another hour or two, or feed once more.
The float test isn't infallible — a starter can fail the float and still bake fine, or float and still be weak — but at day 7 it's a useful sanity check.
If you want to bake right away and need to calculate levain quantities for a recipe, the levain calculator on this site will do the math on how much to build from your new starter.
What "ready" actually means
A day-7 starter can raise bread, but it's a teenager, not an adult. The flavor will be mild-to-flat for the first two or three bakes. Full sour complexity develops over 3–4 more weeks of regular feeding. Don't judge your starter by loaf #1.
Signs it's genuinely ready:
- Doubles in 4–8 hours at room temp after a feed
- Has a strong, even bubble structure — not just a few big holes
- Smells tangy, yeasty, slightly fruity or beer-like — not sharp like vinegar or nail polish remover
- Behaves consistently over three or four feed cycles
Storage once it's established
Feed daily at room temp if you bake often (2+ times a week). Otherwise, move it to the fridge and feed once a week. To feed from cold: discard down to 25g, add 50g flour and 50g water, leave out for 2–4 hours until active, then refrigerate again.
The night before a bake, take it out and give it two feeds at room temp to wake it up fully.
Troubleshooting
Pink, orange, or fuzzy growth
Throw it out. Pink or orange streaks and any fuzzy mold mean contamination. Wash the jar in hot soapy water and start over. Note: a grey liquid on top ("hooch") is not mold — that's alcohol from a hungry but healthy starter. Pour it off or stir it in and feed.
Smells like nail polish remover
Acetone smell means it's starving. Feed more often or use a warmer spot. This is common on day 3–4 and fixes itself.
Won't rise after day 7
Nine times out of ten, it's temperature. Measure your kitchen with a probe thermometer. If it's below 72°F, your starter needs help. The other cause is chlorinated water — switch to filtered.
Rises then collapses fast
It's peaking and falling between checks. Either feed more (larger ratio like 1:5:5) or catch it earlier. A starter that peaks in 3 hours and collapses is strong, not weak — you just need to time your bake to its schedule.
Common questions
Can I use all-purpose flour instead of bread flour?
Yes. All-purpose works fine for maintenance. Bread flour just gives slightly more vigorous rises because of higher protein. The whole grain flour on days 1–3 matters much more than the white flour choice later.
Do I have to use rye, or is whole wheat fine?
Whole wheat works. Rye is faster because it has more accessible sugars and typically carries a heavier microbial load, so it tends to shave a day off the process. Either gets you there.
Why does my starter smell like vomit or vinegar?
Overly sharp, harsh smells usually mean it's too acidic — either underfed or fermenting too warm. Increase the feed ratio (try 1:5:5 instead of 1:2:2) and move it somewhere cooler.
Can I skip discarding to save flour?
Not in the first week. After it's established, you can build smaller starters (as little as 5g mother + 25g + 25g) to minimize waste. But during the build, discarding is what drives pH down and drives the culture forward.
Is the "pineapple juice trick" necessary?
No. Some old guides recommend using pineapple juice on day 1–2 to lower the pH and prevent bacterial off-smells. It works, but it's optional. A standard flour-and-water build gets to the same place by day 4 or 5.
Can I speed this up?
Warmer temperatures (78–82°F) can knock a day or two off, but there's a floor. The microbial succession takes time, and no trick reliably produces a bakeable starter in 3 days. Plan for a week and be pleasantly surprised if it's ready on day 6.
One last thing
The single biggest mistake I see new starters make isn't a technique problem — it's throwing out a starter on day 4 that would have worked on day 6. If your jar smells weird and looks dead midweek, that's the stage where it needs your patience, not your judgment. Set a reminder to feed it, walk away, and check back in 24 hours. The microbes are doing their work whether you're watching or not.