The best sourdough starter I have ever used was made with green grapes. The natural yeast in the air and the sugar in the grapes produces the perfect super-sour-sponge, just like they make in San Francisco. Its so easy and fast to make this starter for bread, pancakes, and crepes. Simply wash and stem 1-pound of seedless green grapes, crush the grapes with a potato masher and place in a bowl. Cover with a muslin cloth or cheesecloth and let set on your kitchen counter for 2 days. Strain the liquid into a 2-cup measuring cup and add water up to the 2-cup level. Add 1-cup of flour and 1-cup of luke-warm water. Mix with a wooden spoon, pour into a quart jar or a large container with a lid. Loosely cover container with the lid and set out on kitchen counter for 24 hours. Feed the sponge again with 1-cup of flour and 1-cup of luke-warm milk (1%, 2% or whole milk is fine) and let set for another 24 hours. If the sponge is bubbly, its ready to use in your favorite recipe.
Replace the sponge used with same amount of flour and water. If your recipe calls for 1 cup of starter. Add 1 cup flour and 1 cup water or milk to the remaining starter and let set in a warm place for 24 hours.
Feed your sponge at least once a week. Remove a cup of starter and replace with 1-cup flour and 1-cup luke-warm water or milk.
Refrigerate if not using sponge within 24 hours of feeding.
Watch this video recipe from Harvest Eating: Sourdough Crepes