Drying grapes naturally and calculating product yield

Grapes must be picked from twigs, sprinkled on a wire rack in one layer and left in a sunny place. The drying process lasts up to three weeks, depending on the weather. The finished product has a moisture percentage of not more than 20%. The disadvantage of drying in the sun is that the grapes lose their original color and become dark brown, the aroma also becomes dull.