How to make a sourdough starter from scratch

To make a sourdough starter, mix equal weights of flour and water in a jar, then feed it fresh flour and water once a day for roughly two weeks. Wild yeast and bacteria already living on the flour do the work. You are just giving them food and time. Expect 10-14 days before it can raise bread, sometimes longer in a cold kitchen.

What you need

• A clean glass jar, around 500ml, with a loose lid or a cloth on top
• A kitchen scale that reads in grams
• Whole rye or whole wheat flour to start, then plain white bread flour
• Lukewarm water, ideally filtered or left to sit overnight if yours is heavily chlorinated

That is the whole kit. Whole grain flour gets things going faster because it carries more wild microbes than white flour, so I use it for the first few days.

Day by day

Timings here are estimates. A warm kitchen (around 24C / 75F) moves fast. A cold one (18C / 64F) drags. Judge by what the starter does, not by the calendar.

Day	Feed	What you should see
1	50g whole rye + 50g water	Nothing yet, just a shaggy paste
2-3	Keep 50g, add 50g flour + 50g water	A few bubbles, a sour-funky smell
4-6	Switch to white bread flour, feed 1:1:1	Rise then fall, maybe a stall
7-10	Feed once daily, 1:1:1	Steady rise, doming, tangy smell
11-14	Feed once or twice daily	Doubles in 4-6 hours

Day 1: combine the rye and water in the jar, scrape down the sides, cover loosely, and leave it on the counter.

Days 2-3: discard all but 50g, then add 50g flour and 50g water. You may see early bubbles and a smell somewhere between yogurt and nail polish. The smell is normal. It settles down later.

Days 4-6: move to white bread flour now. Keep 50g of starter, add 50g flour, add 50g water. This is a 1:1:1 feed by weight. A common dip happens around here where activity stalls for a day or two. Keep feeding. It almost always comes back.

Days 7-14: you should see a reliable rise and fall each day. Once the starter doubles within 4-6 hours of a feed and smells pleasantly sour rather than sharp, it is close to ready.

How to know it is ready

The float test is a quick check. Drop a spoonful into water. If it floats, the starter is full of gas and likely strong enough to bake with. It is not perfect, so I trust the rise more: a starter that doubles predictably and falls on a schedule is ready, float or not.

Other signs to look for:

• Consistent doubling after every feed, day after day
• A network of bubbles through the jar, not just on top
• A clean tangy aroma, more sour cream than acetone

Common problems

• Liquid on top: that grey or brown layer is hooch, a sign the starter is hungry. Pour it off and feed.
• No activity by day 5: warm the spot, switch to whole rye for a feed or two, and check your water for chlorine.
• Pink or orange streaks or fuzzy mould: throw it out and start fresh. That is the one time to bin it.

Once your starter is active, keep it going with regular feeds. See feeding your sourdough starter for a schedule, and use the hydration calculator when you scale a recipe up or down.

After it is ready

When the starter doubles on cue, you can bake. Build a levain the night before by feeding a small amount and letting it ripen overnight. If you bake less often, move the jar to the fridge and feed it once a week. A starter is forgiving. Neglect it for a stretch, give it two or three feeds, and it usually wakes right back up.