Requirements of Rye flour

Appears in
top 1000Bread: A Baker's Book of Techniques and Recipes
Bread

By Jeffrey Hamelman

Published 2004

  • About
Rye flour is significantly different from wheat flour; in fact, from the growing culture of the grains, to the mixing, fermenting, proofing, steaming, baking, and even in the eating, rye differs from wheat. In order to produce rye breads of a consistent high quality, a thorough understanding of rye’s unique requirements is necessary:
  • The Gluten-Forming Proteins Glutenin and Gliadin exist in sufficient quantity in wheat flour to produce doughs that are at once extensible (this is an attribute of gliadin), and at the same time elastic (an attribute of glutenin). Combined, the glutenin and gliadin help provide structure to dough, and in combination they capture the carbon dioxide gases produced by the yeast fermentation, allowing the dough to expand to full leavened volume. Rye flour contains gliadin as well as the protein glutelin (which is similar to glutenin). However, due to the presence of pentosans (see below), gluten formation is not possible, hence rye breads will always have a denser structure than wheat breads.
  • Rye Flour is Higher in Bran and Fiber than Wheat, which means rye breads have higher water absorption. A poolish made with 10 pounds of water and 10 pounds of white flour will be as loose as pancake batter. A similar mixture of 10 pounds of water and 10 pounds of whole rye flour will be considerably thicker. Since rye holds more water, the dough yield from rye breads is higher. While this can be of economic benefit to the baker, the extra water-holding capacity will produce bread with a moist and pasty crumb unless proper care is taken.
  • The Higher Level of Bran and Minerals in Rye has another impact on the bread: As the mineral content of the flour increases, there is a corresponding decrease in bread volume. This is caused because the sharp shape of the bran pieces cuts the gluten network. This is least evidenced when white rye is used, and most visible as more and more dark rye is present in the formula. This cutting property of the bran has an identical effect on wheat breads, which is why the volume of whole-wheat bread is less than that of white bread.
  • Rye has More Soluble Sugars than Wheat, and therefore rye doughs ferment more quickly than wheat doughs. This trait, coupled with rye’s inability to form a wheatlike dough structure, means that rye doughs can quickly overferment and collapse.
  • Rye is High in a Substance Called Pentosans, a polysaccharide substance found in plants. The pentosan content is higher in rye flour (about 8 percent) than in any other flour. The pentosans contribute to the high water absorption of rye breads, and at the same time compete with the glutelin and gliadin in the flour for moisture. This serves to prevent the development of gluten in rye breads. Further, the pentosans are fragile and easily broken, with a resulting potential for rye doughs to become sticky as the flour unknits. As a consequence of this characteristic, rye doughs must be gently mixed (a standard rye bread mixer in Germany, called a Langsamkneter, or slow-speed mixer, rotates at only 25 to 40 rpms, roughly 25 percent of the rpms in a spiral mixer).
  • Rye is a Grain High in Amylase Enzymes (during humid growing seasons, the amylases can be in an advanced state of activity even before the time of harvest). A thorough understanding of the characteristics of amylases, and their potential to damage crumb structure, is essential for the baker of rye breads. Enzymes have one specific activity, and in the case of amylase, the activity it performs is the conversion of starch into sugar. Starches swell with water during the bake, and eventually form the crumb of the bread. Sugars, on the other hand, do not contribute to the formation of crumb structure; in fact, if they exist in too high a proportion in the dough, they have the effect of causing gumminess in the crumb. During the bake, when the internal dough temperatures are between 122° and 140°F, the starches in the rye begin to expand, absorb water, and gelatinize, and the crumb structure of the loaf begins to form. The amylases, however, are in a state of accelerated activity at these temperatures, and are not destroyed by heat until about 176°F. Therefore, they have an opportunity to wreak considerable havoc by breaking down the starch into sugar, and preventing the starch from forming a well-structured crumb. This is the dreaded “starch attack.” The result (unless the baker uses his or her skill) is bread with a gummy, pasty crumb. Wheat flour is exempt from these problems, first because wheat has less amylase than rye, and second because wheat starch gelatinizes at higher temperatures (beginning at about 158°F and ending at about 194°F), giving the enzymes less opportunity to damage crumb structure. The baker of rye breads has one great tool at his disposal to inhibit the decomposing activity of the amylase, and that tool is sourdough. In the presence of acid, the activity of the amylases is slowed down. Therefore, by using sourdough, the baker stabilizes the baking ability of the bread by inhibiting the enzymatic activity that would otherwise result in bread with a gummy crumb.