It is one of the classical grains of ancient times. The cooking characteristics of rye flour are remarkably different from those of wheat flour. This is mainly due to the fact that in rye mixtures, the molecules of gluten (a sticky protein) cannot build any adhesive structure to trap gas because of the presence of pentosans (viscous substances). In rye these viscous substances carry out the same function of gluten in wheat. They are important to bind and retain water during the preparation of the dough and in cooking. Rye bakery products - unlike wheat products - are characterised by a darker, hard and aromatic dough. Rye bread is mainly made up of gelified starch; its crumb is more compact and it contains fewer holes, therefore it is less airy than in wheat bread. Rye flour is often used in multi-grain and wholegrain bread. From a nutritional point of view, rye is low in carbohydrate compared to other grains (65%) and high in protein (16%). It contains good amounts of lysine, an essential amino acid that is low in other grains. It has a fairly low amount of fat (2.6%).