Step 1: In a clean, liter-sized glass jar, combine 50 grams unbleached all-purpose flour, 25 grams instant mashed potato flakes, and 75 grams non-chlorinated water. Mix thoroughly with a non-metal spoon until no dry pockets of flour remain. The mixture will be thick and paste-like.
Step 2: Cover the jar loosely with a lid or plastic wrap, allowing some air to circulate (a coffee filter secured with a rubber band also works well). Place the jar in a warm spot (ideally 70-75°F / 21-24°C) away from direct sunlight. Leave it undisturbed for 24 hours.
Step 3: After 24 hours, check your starter for any small bubbles or faint activity. Discard about half of the starter (approximately 75-80 grams). This step is crucial for managing volume and concentrating the yeast and bacteria.
Step 4: To the remaining starter, add 50 grams unbleached all-purpose flour, 25 grams instant mashed potato flakes, and 75 grams non-chlorinated water. Mix well until smooth. Cover loosely and return to your warm spot for another 24 hours.
Step 5: Repeat the feeding process every 24 hours for the next 4-5 days: discard half of the starter, then add 50g flour, 25g potato flakes, and 75g water. Mix, cover loosely, and return to its warm spot. You should start seeing more consistent bubbling and rising around Day 3-4.
Step 6: By Day 7 (or sometimes sooner), your starter should be consistently doubling or tripling in size within 4-8 hours after feeding. It will be full of bubbles, smell pleasantly yeasty and sour, and pass the “float test” (drop a small spoonful into water; if it floats, it’s ready to bake with!).
Step 7: To maintain, if baking frequently, feed every 12-24 hours. If baking less often, store in the refrigerator and feed once a week (bring to room temp, feed, let activate 2-4 hours, then return to fridge).