Mix 1 cup of rye flour with apple juice or water enough to make a batter (I like to use apple juice). Add a slice of onion. Cover and let it sit for 2 or 3 days. When it begins to smell slightly alcoholic, and sour bubbles appear on the surface, it is ready to use. You can use it now or cover and place in a glass jar and refrigerate (remove the onion). Mix a few tablespoons of fresh flour and liquid into it every 7 days to feed it and keep it fresh and always bring the amount you are going to use to room temp before adding to a recipe. Usually letting it sit on the counter in the measuring cup for 20 minutes is perfect. Also, don't use it again within 24hrs of feeding it so if you need some remove it before you feed.