Originally Posted by edwmax

Here is a recipe from a 1880 Cookbook;



"GOOD HOME-MADE YEAST
Grate six large raw potatoes, have read a gallon of water in which you have boiled three handfuls of hops. Strain through a fine hair sieve, boiling hot, over the potatoes, stirring well, or the mixture will thicken like starch. Add a small cup of sugar and half a cup of salt. When cold, add a cup of fresh yeast. Let it stand until a thick foam rises on the top. Bottle in a couple of days. If kept in a cool place this yeast will last a long time . Use one cupful of yeast for one large baking. In making it, from time to time, use as bowl of the same to raise the new yeast with."



As in most cases you start with a small amount of yeast of some form.