1. Prepare Your Workspace: Gather your sourdough starter jar, unbleached flour, filtered water, a clean spoon or spatula, and a kitchen scale for accuracy.

2. Assess Your Starter: Look at your starter. Does it have bubbles? Does it smell yeasty and slightly sour, like yogurt? If it’s been a while since its last feed, it might look a bit flat or have a layer of dark liquid (hooch) on top, which is normal.

3. Discard Excess Starter: This is a crucial step to prevent your starter from growing too large and to ensure it gets enough fresh food. Gently stir your starter. Measure out about 20-50 grams (or about 2-4 tablespoons) of your active starter into a clean jar. Discard the rest, or save it for discard recipes like crackers or pancakes.

4. Add Water: To your measured starter, add an equal weight of filtered, room-temperature water. For example, if you kept 30 grams of starter, add 30 grams of water. Stir well with a clean spoon or spatula until the starter is fully dissolved in the water and no lumps remain.

5. Incorporate Flour: Now, add an equal weight of flour to the mixture. If you used 30 grams of starter and 30 grams of water, add 30 grams of flour. Mix thoroughly until all the flour is incorporated and there are no dry spots. The mixture should be thick but pourable, like a thick pancake batter.

6. Scrape Down the Sides: Use your spatula to scrape down any flour or starter clinging to the sides of the jar. This keeps your jar clean and helps prevent mold.

7. Mark the Level: Place a rubber band or use a marker on the outside of the jar to indicate the current level of your freshly fed starter. This will help you visually track its rise and fall, indicating its activity.

8. Cover and Rest: Loosely cover the jar with its lid or plastic wrap. Do not seal it tightly, as the starter needs to breathe. Leave it at room temperature (ideally 70-78 F or 21-26 C) until it doubles or triples in size and is bubbly and active, typically 4-12 hours. Once active, it’s ready to use in your baking or can be refrigerated if you won’t be baking soon.