To dehydrate it, simply feed it and spread it on baking paper when bubbly and at its peak. Let it dehydrate naturally with a baking paper sheet in top for 1-2 days. Once fully dried, blitz it - et voila! Next time you want to bake, simply mix a small amount with 3x parts water. Let it sit for 2h or so. Add the same amount of flour as water (1:3:3 ratio). Let it rise and feed again one more time before using. It will be as lively as it used to be!