Create durable "dry starter"

To conserve a starter and have a save backup, you can dry some of your sponge.  (before you mix it with salt or anything else than flour and water). That is very easy: just spread it very thinly onto a sheet of baking paper  and  leave it alone for a day or two until it is absolutely dry. DON'T dry it in the oven: it will get too hot and the yeast-organisms die. This is, how my "rye-dry" backup looked when it was dry:

and after breaking it into small peaces:

put that into a airtight jar at a dark, dry place and you can keep it for years.