Rye bread is bread made with flour from rye grain of variable levels. It can be light or dark in color, depending on the type of flour used and the addition of coloring agents, and is typically denser than bread made from wheat flour. It is higher in fiber than many common types of bread and is often darker in color and stronger in flavor.
While rye and wheat are genetically close enough to interbreed (the resulting hybrids are known as triticale), there are some substantial differences in the biochemistry of wheat and rye that can drastically affect the breadmaking process. A key issue is amylases -- while wheat amylases are generally not heat-stable and have no effect on the stronger wheat gluten, rye amylase remains active at substantially higher temperatures. Since rye gluten is not particularly strong, the main structure of the bread is based on complex polysaccharides, including rye starch and pentosans, and the amylases in the flour can break down the resulting structure, inhibiting the rise of the dough.
There are two common solutions to that. The traditional manner, acidification, uses Lactobacillus cultures in a naturally-derived sourdough starter to inactivate the rye amylases, which cannot function in an acidic environment, and to help gelatinize the starches in the dough matrix. In areas where obtaining wheat has traditionally been impractical because of marginal growing conditions or supply line difficulties, this has been the most important technique to creating lighter breads. As a byproduct of this intentional cultivation of lactic acid and acetic acid from the sourdough bacteria, standard baker's yeast is not often used, since Saccharomyces cerevisiae is known to be rather intolerant of acid environments. (Commercial yeast can, however, still be used; recipes substituting citric acid or vinegar and commercial yeast for the sourdough culture are sometimes used in baking trades.)
In areas where high-gluten hard wheat is readily available, on the other hand, the need for a complex polyculture of bacteria and yeast can often be reduced or removed by adding a large proportion of hard wheat flour to the rye flour; the added gluten compensates for amylase activity on the starch in the bread, allowing it to retain its structure as it cooks. (The Jewish rye bread tradition in the United States is based upon this mixing of grains.) The use of high-gluten wheat flour also makes possible multi-grain breads such as the "rye and Indian" bread of the American colonies, which combined rye and wheat with cornmeal in one loaf.
Pure rye bread contains only rye flour, without any wheat. German-style Pumpernickel, a dark, dense, and close-textured loaf, is made from crushed or ground whole rye grains, usually without wheat flour, baked for long periods at low temperature in a covered tin. Rye and wheat flours are often used to produce a rye bread which has a lighter texture, color and flavor than pumpernickel. 'Light' or 'dark' rye flour can be used to make rye bread; the flour is classified according to the amount of bran left in the flour after milling. Caramel or molasses for coloring and caraway seeds are often added to rye bread (in the United States, breads labeled as "rye" nearly always contain caraway unless explicitly labeled as "unseeded"). Typically, rye bread recipes often include ground spices such as fennel, coriander, aniseed, cardamom, or citrus peel. In addition to caramel and molasses, ingredients such as coffee or cocoa (or even toasted bread crumbs) can also be used for both coloring and flavor purposes for very dark breads like pumpernickels.
A simple, all-rye bread can be made using a sourdough starter and rye meal; it will not rise as high as a wheat bread, but will be moister with a substantially longer keeping time. Such breads are often known as "black breads", partly from their darker color than wheat breads (enhanced by long baking times creating Maillard reactions in the crumb), partly from their perceived lower social status than the lighter, more expensive wheat breads. The German Vollkornbrot ("whole grain bread") is something of an archetypical example, containing both rye meal and cracked whole rye grains (which are generally soaked overnight before incorporating into the dough). It is used both as an appetizer substrate for such things as smoked fish and caviar and as a sandwich bread. (A very similar but darker bread, German-style pumpernickel, has an even darker color derived from toasted leftover bread and other agents.) Due to the density of the bread, the yeast in the starter is used at least as much for the fermentation character in the bread itself as it is for leavening.
As stated above, all-rye breads have very long keeping times measured in months rather than days, and are popular as storage rations for long boat trips and outdoors expeditions. Such breads are usually sliced very thin because of their density, sometimes only a few millimeters thick, and are sold pre-sliced in this manner.
It is fairly common to combine rye with other grains and seeds. In southern Germany and Switzerland, for example, it is not uncommon to find a variant of Vollkornbrot with sunflower seeds instead of the rye seeds, and some traditional recipes also substitute whole wheat grains for the rye grains. In the colonial era in North America, particularly in the United States, it became common to mix rye and cornmeal in what was known as "rye and indian" or, if wheat flour was added, "thirded" bread; the resulting bread, though less dense than a whole-rye bread, was still heavier than the more expensive wheat-only breads that later became commonplace.
Wheat-rye breads, particularly light rye (also known as "sissel") and American pumpernickel but also a combination known as "marble rye", are very closely associated with Jewish-American cuisine, particularly the delicatessen. The bulk of the flour is white wheat flour (often a less-refined form known as "first clear"), with a substantial portion of rye mixed in for color and flavor. The dough is often but not necessarily leavened, in whole or in part, with sourdough, but sometimes uses a small addition of citric acid or vinegar to achieve the lowered pH needed to neutralize the rye amylases; so-called "Jewish rye" is further seasoned with whole caraway seeds and glazed with an egg wash, and is traditionally associated with salted meats such as corned beef, pastrami, and (outside kosher circles) ham. High-gluten wheat flour can be used with rye flour to make a dough suitable for bagels as well. Jewish-style American rye bread is sometimes referred to as "corn bread" or "corn rye"; the term comes from the use of cornmeal as a coating and handling aid and does not necessarily imply the use of cornmeal within the dough itself as in Rye and Indian.
The Jewish-American variety has Eastern European antecedents, including Russian-style brown bread and Riga-style rye bread. In Scandinavia, similar breads are made, some of which also include sweeteners and/or citrus peel, as well as spices such as fennel or cardamom, when made for more festive occasions (such as in the Swedish limpa).
One of the largest producers of rye flatbreads, and one of the most prominent in overseas markets, is the Swedish-founded company Wasabröd.
Rye flour is sometimes used in chemically-leavened quick bread recipes as well, either batter-type or dough-type (similar to Irish soda bread). In such cases it can be used in similar applications as whole wheat flour, since an egg matrix often provides the bread structure rather than the grain's gluten.
In 500 AD., the Saxons and Danes settled in Britain and introduced rye which was well suited to cold northern climates. Dark rye bread became a staple which lasted to the Middle Ages. Many different types of rye grain have come from all over Europe such as Finland, Denmark, Russia, and the Baltic countries but rye bread originates from Germany. In Finland, Estonia, Denmark and Russia, rye is the most popular type of bread. A common saying in modern day Alaska is "eggs on rye" which is an expression used when something tastes delicious.
Rye is a popular bread for sandwiches. In the United States, pastrami on rye is particularly popular; it is considered a classic element of Jewish-influenced New York City cuisine.