Raisins are sweet due to their high concentration of sugars (about 30% fructose and 28% glucose by weight). The sugars cancrystallise inside the fruit when stored after a long period, making the dry raisins gritty, but that does not affect their usability. These sugar grains can be dissolved by blanching the fruit in hot water or other liquids.Raisins are produced commercially by drying harvested grape berries. In order for a grape berry to dry, water inside the grape must be removed completely from the interior of the cell onto the surface of the grape where the water droplets can evaporate. However, this diffusion process is very difficult because the grape skin contains wax in its cuticle, which prevents the water from passing through.In addition to this, the physical and chemical mechanisms located on the outer layers of the grape are adapted to prevent water loss.