The grape starter is from Julia Child's new Master Chef book($17.95 Retail). It is a recipe given by Nancy Silverton. It takes 10 days to complete but is then yours for life.
Wrap the grapes in well washed cheesecloth, tieing the corners to form a bag; lightly crush them with a rolling pin (to release the sugar to mix with the natural yeast on the skins; just like making wine!) and immerse them in the flour water mix. Cover tightly with a lid or plastic wrap secured with a rubber band. Leave at room temperature for 6 days, stirring once or twice a day for the six days.
The bag of grapes will eventually appear inflated, and liquid will begin to separate from the flour base. The mixture will begin to taste and smell slightly fruity, and the color will be strange. That is as it should be. By the sixth day the bag of grapes will have deflated, the color will be yellow, and the taste pleasantly sour; the fermentation is complete. The starter is living but weak, and it needs to be fed.
Remove the grapes and squeeze their juices back into the starter. Stir it up thouroughly and transfer it to a clean container. (Although you can use it after just one feeding, the starter will be stronger and healthier with the full treatment) You can refrigerate it until you're ready to proceed.
Three days before you plan to use it, stir 1 cup flour and 1 cup water into the container, blending well. Let stand uncovered at room temperature until it bubbles up - 3 to 4 hours - then cover and refrigerate. Repeat this for the second and third day.
Store the starter tightly covered in the refrigerator where it will keep perfectly for 4 to 6 months.- after which it's a good idea to pour off all but 2 cups and give it another feeding. Before using the stored starter for bread, however, give it the full 3-day feeding schedule once again to restore it and to tone down excess sourness.
This is the starter for Nancy Silverton's Olive Bread recipe. From: Richard Taylor