Tamara asked me to post this recipe, I use it all the time now.
Peel two medium sized potatoes and grate them into a plastic bowl, pour 2 cups of boiling water in them and stir until sort of thich like. Cool to lukewarm. Then put two packages of yeast that you have dissolved into the mixture and stir.
Add 1/2 cup of sugar, stir in and set aside with a towel over the top. It will all bubble and when through bubbling take out all but one cup and use for the yeast called for in your recipe and put the left over cup in the fridge. The day before you are ready to make bread again, take out your cup of yeast and start over with the raw potatoes again and when this has cooled to lukewarm add the yeast that you saved, add 1/2 cup of sugar again and set aside to bubble. Always save a cup when you use it to keep your yeast active. You should keep this yeast fresh every couple of weeks at the least.
And there you have it. Any questions? I hope I explained it well enough for all of you who are interested.