On Day 1, combine 50 g whole-grain flour and 50 g water in a clean glass jar. Stir until no dry flour remains, cover loosely, and leave at room temperature for 24 hours.

On Day 2, stir the mixture and check for bubbles or a slightly sour smell. If there is visible activity, discard approximately half, then add 50 g flour and 50 g water; if activity is minimal, wait and continue feeding once every 24 hours.

From Days 3–7, once fermentation is clearly active, retain 50 g starter and discard the remainder. Add 50 g flour and 50 g water, mix thoroughly, scrape down the jar, and mark the starting level.

Repeat the feeding every 24 hours. If the starter rises and falls within 12 hours, feed it twice daily instead.

Use the starter near its peak after feeding, when it has doubled in volume and the surface is domed or just beginning to flatten. A float test may support your observations, but consistent rise and bubbling are more dependable signs.