A sourdough starter is just flour and water left to capture the wild yeast and bacteria already living on the grain and in your kitchen. You do not need a packet of yeast, a sourdough "sample," or any special equipment. You need a clean jar, a kitchen scale, and about a week of attention.

The seven-day plan - Day 1: Mix 50g whole wheat or rye flour with 50g lukewarm water in a jar. Stir, cover loosely, and leave at room temperature. - Days 2-3: You may see a few bubbles and a slightly sour smell. Discard all but about 50g, then feed with 50g flour and 50g water. - Days 4-6: Switch to all-purpose or bread flour. Feed once or twice daily, discarding down to 50g each time. The starter should start rising and falling predictably. - Day 7: It should roughly double within 4-6 hours of feeding, smell pleasantly tangy, and be full of bubbles.

How to know it is ready The classic test is the float test: drop a teaspoon of starter into water. If it floats, it is full of gas and ready to bake with. A reliable starter doubles in size and domes on top a few hours after feeding.

Keeping it alive Once established, you can store the starter in the fridge and feed it once a week. Pull it out and give it two feedings at room temperature before you plan to bake.

Common early mistakes Do not give up on day 3, when activity often stalls. This is normal as the bacterial culture shifts. Keep feeding on schedule, keep it warm, and it will recover. Cold kitchens simply take longer.