Overview
Rye bread is a type of bread made with various proportions of flour from rye grain. 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. Compared to white bread, it is higher in fiber, darker in color, and stronger in flavor. The world's largest exporter of rye bread is Poland.
Rye bread was considered a staple through the Middle Ages. Many different types of rye grain have come from north-central, western, and eastern European countries such as Iceland, Germany, Austria, Denmark, Sweden, Norway, Finland, Estonia, Latvia, Lithuania, Poland, Belarus, Ukraine, Russia, the Netherlands, Belgium, France, and the Czech Republic, and it is also a specialty in the canton of Valais in Switzerland. Around 500 AD, the Germanic tribe of Saxons settled in Britain and introduced rye, which was well-suited to its temperate climates.
Biochemistry
While rye and wheat are genetically similar enough to interbreed (resulting in hybrids known as triticale), their biochemistries differ enough that they affect the breadmaking process. The key issue is differing amylases, the enzyme which breaks starch down into sugar. While wheat amylases are generally not heat-stable and thus do not affect stronger wheat gluten that gives wheat bread its structure, rye amylase remains active at substantially higher temperatures. Since rye gluten (secalin) is not particularly strong, rye dough structure is based on complex polysaccharides, including rye starch and pentosans. As a result, amylases in rye flour can break down dough structure, inhibiting it from rising.
From Wikipedia (CC BY-SA 4.0).