Sourdough Starter From Scratch: The 7-Day Process

A sourdough starter is a culture of wild yeast and lactic-acid bacteria that lives in a jar of flour and water. Once it's established, it replaces commercial yeast in any sourdough recipe — and unlike commercial yeast, a starter develops the complex sour, fruity, faintly tangy flavor that defines real sourdough.

Building one from scratch is mostly waiting. Mix equal weights of whole-grain flour and water in a jar, leave it on the counter, and feed it once a day for about a week. The wild yeast and bacteria are already on the flour and in the air; you're creating the conditions for them to wake up and outcompete everything else. This guide walks through the seven-day process step by step, what readiness actually looks like, and what to do about the most common things that go wrong.

What you need

• A glass jar, roughly 16 oz / 500 ml capacity, with a loose-fitting lid or cloth cover. A mason jar with the lid laid on (not screwed down) works. The jar needs air exchange — sealed-tight containers trap CO₂ and turn the starter alcoholic and unhappy.
• A digital kitchen scale. Volume measurements of flour are unreliable enough to be a real problem here. A $15 scale solves it.
• Whole-grain flour for the first 3-4 days: rye is best, whole wheat is second-best. Both carry more wild yeast and minerals than refined flour, which jumpstarts fermentation.
• All-purpose or bread flour for the rest of the build. Either works. You can stay on whole-grain the whole time if you prefer; the starter will be a little more active and a little more sour.
• Filtered or spring water, room temperature. Chlorinated tap water can inhibit fermentation in the first few days — letting tap water sit out overnight for the chlorine to off-gas works, or use bottled. Once the starter is established it can handle chlorinated tap fine.

The 7-day schedule

Day 1 — Mix

In the jar, weigh 50g whole-grain flour and 50g room-temperature water. Stir until no dry flour remains. The mixture will look like a thick paste. Mark the level on the jar (a rubber band works) so you can see if it rises. Cover loosely and leave on the counter at normal room temperature (around 68-75°F / 20-24°C).

Nothing visible will happen for a day or two. That's normal — the yeast and bacteria are slowly waking up and starting to consume the flour's natural sugars.

Day 2 — Watch, no feed yet

Check the jar. You may see a few bubbles starting to form on the sides; you may see nothing. Either is fine. Don't feed yet. Replace the cover and wait.

Day 3 — First feeding

You should see distinct bubbles in the mixture now and probably a slight rise. The smell will be unusual — sometimes pleasantly fruity, sometimes funky and cheese-like, sometimes mildly off. All of these are fine at this stage; the bacterial community is still settling.

Begin daily feedings. Discard about 50g of the starter (roughly half), leaving 50g in the jar. Add 50g flour and 50g water to what remains. Stir well to combine. Mark the new level. Cover and wait 24 hours.

The discard isn't waste: even at this early stage, the discarded mixture is just flour and water that's been sitting around. Pour it into a discard jar in the fridge and use it for pancakes, crackers, or quick breads. See the discard section near the end for ideas.

Day 4 — Second feeding

The mixture should be noticeably more active now — more bubbles, more rise (maybe doubling within 12-24 hours), a more recognizable yeasty smell. Discard half. Feed with another 50g flour + 50g water. If you started with whole-grain, you can switch to all-purpose or bread flour now if you prefer (or stay on whole-grain — it makes a punchier starter).

Days 5-7 — Keep feeding, watch the rise pattern

Continue the same daily feeding routine: discard about half, add 50g flour + 50g water, stir, mark the level. Each day the starter should rise predictably faster after a feed. By day 5-6, you should see the starter roughly double in size within 6-8 hours of feeding, then slowly collapse back over the next 12-18 hours.

This predictable rise-and-fall pattern is what tells you the starter is establishing. The first few days' bubbling activity is often dominated by the wrong microbes (leuconostoc bacteria, which produce CO₂ but not the right flavor); by day 5-6 the wild yeast and lactobacilli have taken over and the starter behaves like the one you want.

Day 7+ — Readiness check

Most starters are ready to bake with by day 7-10. Specifically, ready means: after a feeding, the starter consistently at least doubles within 4-8 hours, looks domed and full of bubbles throughout (not just on the surface), and smells pleasantly yeasty and tangy — like green apples, beer, or fresh yogurt depending on the bacterial mix.

The float test, and what it actually proves

The standard readiness check is the float test. After feeding, wait a few hours until the starter looks visibly active. Drop a teaspoon of starter into a glass of room- temperature water. If it floats, the starter is at peak activity and ready to bake with. If it sinks, it's either not ready yet or already past peak.

The float test works because peak-active starter is full of trapped gas — enough to be less dense than water. It's a useful binary signal, but it's not perfect: thicker starters (lower hydration) tend to float more reliably than thin ones, and some healthy starters never float well. A starter that doesn't float but otherwise rises predictably and smells right is fine to use.

The four most common failures

1. Slow start (no activity by day 3)

Your kitchen is cold, your flour is too refined, or both. The fix: move the jar to a warmer spot (top of the fridge, inside a turned-off oven with the light on, near a heat vent), and switch to rye or whole wheat if you started with all-purpose. Give it another 2-3 days at the warmer temperature before declaring it dead.

2. Hooch (a layer of dark liquid on top)

That's alcohol from over-fermentation — the starter ate everything you fed it and is hungry. It's not ruined. Either pour the hooch off (slightly sharper-tasting starter) or stir it back in (mellower), then feed normally. Going forward, feed more often or use a slightly larger feeding ratio (1:2:2 — one part starter, two flour, two water — instead of 1:1:1).

3. Mold (fuzzy spots, usually pink, orange, green, or black)

This is the only situation where you should restart. Visible mold means the wrong microbes won the competition. Throw out the starter, wash the jar with hot soapy water (don't use bleach — residual bleach kills future starters), and begin again with cleaner technique. Mold is rare after day 3 once an active starter is acidifying its environment, but it can happen early or if you use a contaminated tool.

4. Pink, orange, or otherwise lurid color

Bacterial contamination — usually a Serratia species. Almost always paired with a distinctly bad smell (rotten, not just funky). Restart with a clean jar. As with mold, this is uncommon if the starter establishes normally.

What to do with the discard

Pouring fresh starter down the drain feels wrong, and it doesn't have to. The discard from each daily feeding is just flour and water that's been sitting on the counter — it works in almost any recipe that uses a flour-and-water component.

The practical move: keep a second jar in the fridge labeled “discard”. Each day after feeding the main starter, pour the discarded portion into that jar. It builds up over a week, doesn't need feeding, and stays useful for weeks in the fridge. Use it for:

• Pancakes and waffles: substitute a cup of discard for a cup of the flour/liquid combo in your usual recipe. The tang comes through and the texture is slightly more tender.
• Crackers: discard + a little oil + salt + your favorite seeds, rolled thin and baked at 350°F. Great way to use a lot of discard in one go.
• Quick breads (banana bread, cornbread, biscuits): the discard replaces some of the flour and liquid. The acidity also makes biscuits and quick-bread cakes rise better when paired with baking soda.
• Pizza dough: a tablespoon or two of discard in a same-day pizza dough adds flavor depth without changing the rise.

Maintenance once it's established

After the starter is reliably active, you have two maintenance modes depending on how often you bake.

Counter mode — for baking 2+ times per week

Keep the starter on the counter and feed it once a day at the same time. Skip the discard step (or just discard less) if you're about to bake. The starter stays ready-to-use all the time, and the flavor stays mild and yeasty.

Fridge mode — for baking once a week or less

Move the starter to the fridge after a feeding. The cold slows fermentation to a crawl, so you only need to feed once a week or so. When you want to bake: pull the starter out, feed it normally, leave on the counter until active (usually 4-12 hours depending on how long it's been refrigerated), then build your levain. This is the most common home-baker pattern.

Refreshing the starter before a bake

A starter straight out of the fridge isn't ready to bake with. The cold slows the yeast so dramatically that even a peak-active fridge starter has only a fraction of the leavening power of a freshly-fed counter starter.

Before any bake: feed the starter 4-12 hours ahead at a 1:5:5 ratio (e.g., 10g starter + 50g flour + 50g water). Wait until it's domed, bubbly, and either floats or has clearly more than doubled. THEN build your levain or use it directly in the recipe. Skipping this step is the most common reason home sourdough doesn't rise, even when the starter itself is healthy.

The library's country sourdough recipespells this out as the explicit first step before the levain stage. For other sourdough recipes you find online, assume this prerequisite even when it's not stated — it's baked into how every professional sourdough timeline works.

The first bake

Don't test your fresh starter on an elaborate recipe. The country sourdough is the right first bake: it's forgiving, the timeline is well-documented, and any starter problems show up as obvious symptoms (a flat loaf means weak starter; a fast over-proof means starter was too strong). After two or three rounds of that, the starter's rhythm and your kitchen's conditions are familiar enough that anything else in the sourdough world is approachable.

Expect your first loaf to be imperfect. That's normal. By the third or fourth bake you'll know how to read your specific starter's timing and what your kitchen's temperature does to it. After that, the starter becomes the most useful single thing in your kitchen — endlessly renewable, freely scalable, and the source of bread that no commercial yeast can match.