Rye bread is made from rye rather than wheat. Both are genetically similar enough to interbreed, but the biochemistry of rye makes the ultimate taste substantially different. Pumpernickel is a German style dark bread using rye and baked for long periods at low temperatures. This results in extremely dense and flavorful bread.
The traditional type is made using a sourdough starter and rye meal. The color can be manipulated from very light brown to very dark. Rye does not rise as much as wheat products, but is moister and lasts months rather than days. It is extremely popular in Northern Europe as an appetizer with smoked fish or caviar. It is also excellent for sandwiches. Multigrain wheat and rye breads predominate in Eastern Europe and in the south of Germany. One combination called sissel is seasoned with caraway seeds provides the primary bread used in Jewish delicatessens. In Scandinavia, these breads have added sweeteners or citrus, and are primarily used for festive occasions.
When this bread is baked without any leavening, it creates crisp thin bread which is considered a delicacy, and bears a relationship to hard tack. All of these breads have strong distinctive tastes.