Pumpernickel is a type of very heavy, slightly sweet rye bread traditionally made with coarsely ground rye. It is now often made with a combination of rye flour and whole rye berries. It has been long associated with the Westphalia region of Germany. The first written mention of the black bread of Westphalia was in 1450. While it is not known whether this, and other early references, refer to precisely the bread that came to be known as pumpernickel, there has long been something different about Westphalian rye bread that elicited comment. The defining characteristics of Westphalian pumpernickel are coarse rye flour—rye meal—and an exceedingly long baking period. The long slow baking is what gives pumpernickel its characteristic dark color. The bread can emerge from the oven deep brown, even black. Like most all-rye breads, pumpernickel is traditionally made with a sourdough starter; the acid preserves the bread structure by counteracting the highly active rye amylases. That method is sometimes augmented or replaced in commercial baking by adding citric acid or lactic acid along with commercial yeast.
Traditional German pumpernickel contains no coloring agents, instead relying on the Maillard reaction to produce its characteristic deep brown color, sweet dark chocolate coffee flavor, and earthy aroma (however, it is not uncommon to use darkly toasted bread from a previous batch as a coloring agent). Loaves produced in this manner require 16 to 24 hours of baking in a low temperature (about 250°F or 120°C) steam-filled oven. The bread is usually baked in long narrow pans that include a lid. Like the French Pain de mie Westphalian pumpernickel has little or no crust. It is very similar to rye Vollkornbrot, a dense rye bread with large amounts of whole grains added.
True German pumpernickel is produced primarily in Germany, though versions of it are sometimes made by specialty bakers outside its homeland. German pumpernickel is often sold in small packets of pre-sliced bread. It is usually found in markets aimed at an upscale clientele because German pumpernickel is often paired with caviar, smoked salmon, sturgeon, and other expensive products of the hors d'oeuvres tray. Because of its association with expensive hors d'oeuvres it can be found throughout Europe, including in the United Kingdom, in upscale groceries, as it is in the United States and Canada.
A separate pumpernickel bread tradition has developed in North America. The American pumpernickel loaf approximates the dark color of traditional German pumpernickel by adding molasses, coffee, cocoa powder, or other darkening agents. In addition to coloring and flavor agents, American bakers often add wheat flour (to provide gluten structure and increase rising) and commercial yeast (to quicken the rise compared to a traditional sourdough). Because of the ways in which American bakers have changed the original German recipe, and for economic reasons, they tend to eschew the long slow baking that is characteristic of German pumpernickel. The result is a loaf that resembles commercial American rye bread -- a bread made with a mix of wheat and rye flour -- but with darker coloring. Many bakers also add a significant amount of caraway seeds, providing an alternate flavor that is now characteristic of many American commercial pumpernickel (and light rye) breads.
American pumpernickel loaves are almost always baked without a baking pan, resulting in a rounded loaf. These breads do not have the dense crumb of a traditional German pumpernickel, and have a rather different flavor profile derived from the added darkening agents and the faster baking process.
The Philologist Johann Christoph Adelung states about the Germanic origin of the word, in the vernacular, Pumpen was a New High German synonym for being flatulent, a word similar in meaning to the English "fart", and "Nickel" was a form of the name Nicholas, an appellation commonly associated with a goblin or devil (e.g., "Old Nick", a familiar name for Satan), or more generally for a malevolent spirit or demon. See also the metal nickel, probably named for a demon that would "change" or contaminate valuable copper with this strange metal that was much harder to work. Hence, pumpernickel is described as the "devil's fart", a definition accepted by the Stopes International Language Database, the publisher Random House, and by some English language dictionaries, including the Merriam-Webster Dictionary. The American Heritage Dictionary adds "so named from being hard to digest." A variant of this explanation is also given by the German etymological dictionary "Kluge" that says that the word pumpernickel is older than its usage for the particular type of bread and may have been used as a mocking name for a person of unrefined manners ("farting nick") first. The change of meaning may have been caused by its use as a mocking expression for the (in the eyes of outsiders) unrefined rye bread produced by the Westphalian population.
The Oxford English Dictionary, however, does not commit to any particular etymology for the word. It suggests it may mean a lout or booby, but also says, "origin uncertain". The OED currently states the first use in English is from 1756. However, there is an earlier use. An eight page drinking song titled "Beef and Butt Beer, against Mum and Pumpernickel" was published in London in 1753.
There is, as well, an often quoted story of how Napoleon while invading Germany was brought dark German rye bread for dinner. He declared that he wouldn't eat it and said instead: "C'est pain pour Nicole!". In other words, it wasn't for him but for his horse, Nicole. "Pain pour Nicole" over time became Pumpernickel. However, according to The Straight Dope, the Napoleon story is an example of folk etymology.