Choose a clean glass jar (quart-size works well) and a breathable cover (lid loosely set or cloth + rubber band)
Gather ingredients: whole wheat or rye flour (optional but helpful) and water (filtered or non-chlorinated if possible)
Day 1: Mix 50 g flour + 50 g water in the jar; stir until no dry spots; cover loosely
Day 2: If you see bubbles, discard half (about half the starter) and add 25 g flour + 25 g water; stir; cover
Day 3: Discard half; add 25 g flour + 25 g water; stir; cover
Day 4: Discard half; add 25 g flour + 25 g water; stir; cover
Continue daily feedings (discard half, then add equal weights of flour and water) until it doubles in size within 4–8 hours after feeding
If using white flour, switch gradually after bubbles appear (e.g., 25% whole grain at first, then increase)
Keep starter in a warm spot (about 70–78°F / 21–26°C)
If it smells very unpleasant (like strong acetone/solvent), feed more frequently (every 12 hours) until it stabilizes
Once ready: feed 1:1:1 by weight (starter:water:flour) and use when it reliably doubles in 4–8 hours
For storage: refrigerate after it’s established; feed weekly (discard and refresh), or feed every 1–2 weeks if very active
To use after refrigeration: feed 1–2 times at room temperature until it’s active and doubles predictably