(Container for mixing starter should be large enough to allow mixture to double in bulk. Always use a nonmetal container and plastic or wooden spoons. Metal containers and utensils produce an undesirable flavor.)
In a large nonmetal container or bowl, dissolve yeast and sugar or honey in water. Let stand until foamy, 5 to10 minutes. With a wooden or plastic spoon, stir in milk powder and flour. Small lumps in batter will be dissolved by fermentation process. Cover container with 2 to 3 layers of cheesecloth; secure with an elastic band. Set in a warm place free from drafts. Stir mixture several times each day. (Clear liquid that rises to the top of the starter should be stirred back into it several times a day.)
Let stand 3 to 5 days until starter has a pleasant sour aroma and is full of bubbles.
Notes
Note: If starter turns orange or pink, undesirable bacteria have invaded it. Mixture must be discarded.To use starter, remove amount called for in recipe; bring to room temperature before preparing sponge.Once starter is made, it may be refrigerated indefinitely,as long as it is replenished every 2 weeks.To replenish starter, add equal amounts of flour and water. For instance, if you use 1 cup starter, replenish by adding1 cup flour and 1 cup water. Cover and let stand in a warm place overnight. Cover and refrigerate.If refrigerated starter is not used for 2 to 3 weeks,remove 1/2 cup and discard, or give it to a friend. Replenish as directed above.