Soften 1 package active dry yeast in 1 quart lukewarm water in a large crock or bowl. Add 2 Tbs sugar and 4 cups all-purpose flour. Beat to mix. Cover with a towel and place in a warm place to sour for 2 to 4 days. After mixture has reached desired sourness, keep in the refrigerator.
If starter is not used often, stir flour and water into it every 10 days to keep it fresh and active.