These carbohydrates or sugars are the primary oxidation products of polyhydric alcohols and are composed of carbon atoms, OH groups and an aldehyde group. They are classified according to their molecular size into monosaccharides (single sugars), oligosaccharides (multiple sugars) and polysaccharides (chains of monosaccharides, such as starch and cellulose). Disaccharides (disaccharides) are a subgroup of oligosaccharides (there are also tri- and tetrasaccharides). The most important (disaccharide) sugar in grape must is sucrose.