Amish Friendship Cake Starter

Dissolve yeast in 1/2 cup water. Stir in 1 1/2 cups water, flour, salt and sugar. Beat until smooth. Let stand, uncovered, at room temperature 3 to 5 days, stirring 2 to 3 times each day. Cover at night. When ready, mixture should have a yeasty but not sour smell. Pour out 1 cup of the starter to use in friendship mixture. To keep this starter, to the leftover starter add 1/2 cup water, 1/2 cup flour and 1 teaspoon sugar. Let stand until bubbly and well fermented, at least 1 day, then store covered in t