Pour your sourdough discard onto parchment paper. Spread it thinly and evenly using a spatula or the back of a spoon. Try to maintain an even thickness throughout.

Place the baking sheet with the parchment paper and the starter trays with the spread sourdough starter into the oven. Leave the oven off and leave it in there for a few days. Check daily to see if it's completely dry and no wet or gummy starter is left. (make sure no one turns on the oven). Depending on the thickness of the starter, it can take up to a week to fully dry.

Break into small pieces and grind in your coffee grinder to a very fine powder like consistency.

Transfer the dehydrated sourdough starter powder into a clean, airtight container. Store it in a cool, dry place away from direct sunlight. Properly stored, dehydrated sourdough starter can last for several months to years. You can also store it in the freezer, in a airtight container.