The keeping and the preparation of fresh produce after harvest affects its nutritional value in several ways, for example:  Dry-matter content (the energy supply) is reduced with time as the continuation of living processes within the produce uses up stored food reserves.  Vitamin C content decreases with time after harvest, and little may remain after two or three days.  Cooking partially destroys vitamins C and B1. Raw fruit and vegetables are particularly valuable provided they are grown and handled hygienically.  Peeling may cause significant loss of food value, especially in potatoes, where the protein content is just beneath the skin.  Water used in cooking vegetables or fruit contains the dissolved minerals and trace elements of the food and should not be thrown out but used in soups or in preparing other foods.