I try to keep 10 quart jars of starter. What I do I put a quarter cup of DME in each jar top it up with water. Put it in the pressure cooker with the lids on make sure you put the rings on loosely. Start the cooker going after it is up to temp cook it for 15 minutes. Once you can open the cooker tighten the rings. Now your starter is shelf stable. Just crack one open and shake it up. Pitch your yeast into the jar.