Dissolve yeast in 1/2 c. Warm water. Let stand 5 minutes. Combine next 3 ingred. In a med. Sized nonmetal bowl. Mix well. Gradually stir in 2 c. Warm water. Add yeast mixture and mix well. Cover loosely and let stand for 72 hrs. In a warm place stirring 2-3 times per day. Place fermented mixture in refrgerator, and stir daily; use within 11 days. To use, remove sourdough starter from refrigerator and let stand at room temp. For at least 1 hour. Stir well and measure amount of starter needed for recipe. Replenish remaining starter with Herman Food, and return to the refrigerator; use within 2-14 days, stirring daily. Yield: about 2 c. Starter Herman Food: 1/2 c. Sugar, 1 c. Flour, 1 c. Milk