Make Jar Yeast

I found this recipe in a 1960's Amish cookbook:

"Pare one small potato and boil until soft, then mash it and have enough water with it to scald 2 tbsp. bread flour, 2 tbsp. sugar, and a pinch of salt. Let cool, then add 1/2 package dry yeast, in a little water, set aside to rise. When nice and light, put in jar with a little cold water.

This may be used instead of compressed yeast, always saving about 2 cups for the next baking. Store in refrigerator. This may be done for a long time, but occasionally a fresh starter needs to be made." ~ Mrs. Mary A Swarey