Gerstel is an Austrian drying method to better keep your rye sourdough when not in use. It calls for mixing your sourdough with three times the amount of rye flour, then storing it in a mason jar. It will keep a week or two. To reactivate, try what's known as a "Detmolder 3-stage Process," as described in 2006 by this generous commentator on Sourdough. When you need to transport your sourdough, or give it to a friend, don't go with a messy bubbling sample. Dry and refresh it.