Yeast Cakes

it can be kept for months.

From 1911:

Take one quart of fresh buttermilk and put it in a double boiler and heat to boiling point; carefully sift in enough white cornmeal to make as thick as gruel. Remove from the fire and cool to lukewarm. Have soaked two yeast cakes in just enough water to cover; when the gruel is lukewarm add the yeast cakes and let stand two hours in a warm place, being careful not to get too hot; at the end of two hours the mixture will be fermenting and then add sufficient cornmeal to make into cakes. Put it on the bread board and make a loaf, and then it can be cut in cakes all the same shape.
Place on a board and dry in the sun, being careful to bring in at night.
When thoroughly dry it is ready for use. Put in tin cans and it can be kept for months.