The 4-cup batch of starter made by this recipe is enough to bake any of the rye breads requiring a rye starter, with enough left over to serve as the nucleus for another baking. When you "feed" leftover starter. . . which should be done every 2 weeks or so. . add a little rye flour and water, using 3 parts of flour to 2 of water. To build up a small amount of starter to a quantity large enough for baking, do the job in several steps, never adding a larger measure of flour than the amount of starter on hand. Let the starter stand at room temperature overnight or for up to 24 hours, until it is bubbly and no longer smells floury. To increase further, add more flour and water in the same proportions and again let the starter ferment until it is bubbly enough to use. Store leftover starter in the refrigerator between bakings and "feedings, " and for indefinite storage, freeze it. Thaw, then feed the starter and let it ferment at room temperature before use. Makes about 4 cups.
Dissolve the yeast in 2 cups of the tepid water, then beat in 2 cups of the rye flour, beating until no lumps remain. Add the onion, cover loosely with a cloth, and let stand at room temperature for 24 hours.
Remove the onion. Beat in 1 cup tepid water, then 1 1/2 cups rye flour. Cover with the cloth and let stand for 24 hours longer. The starter should now be pleasantly sour-smelling, almost beery, and bubbly. (Depending upon the temperature of the room, a slightly longer or shorter period of fermentation may produce this result. ) TO USE: The starter is now ready for use and can be refrigerated for up to 24 hours before use, without further feeding. If you must hold the starter longer before use, the night before it is wanted, add 1/2 cup tepid water and 3/4 cup rye flour and let is stand at room temperature overnight.