Mix ingredients well in a large crockery jar or nonmetallic bowl. Add 2-1/2 cups warm water; mix well. Cover loosely; let stand in a warm place (90-100 F) 2 to 4 days, stirring several times daily. To use, place in a large nonmetallic bowl; add 2 cups flour and 2 cups water. Cover loosely; let stand 12 to 14 hours. Remove amount needed and refrigerate remaining starter. To use again, add more flour and water and repeat the process.