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.
There are many advantages associated with the use of sourdough in rye breads. Certainly one is that the presence of sourdough inhibits the starch attack and allows the baker to obtain good characteristics in the finished loaf. Another pertains to phytic acid, a substance found in the bran coating of cereal grains. Phytic acid interferes with the body’s ability to absorb calcium, zinc, iron, magnesium, and copper. Phytase is a thermo-resistant flour enzyme that is at its most active as dough pH reduces. When dough is acidified with a sourdough phase, the phytase virtually eliminates the effects of phytic acid, making the bound nutrients available and improving the nutritional profile of the bread.
Other benefits connected with the use of sourdough include the leavening power of a healthy sourdough culture, and the vastly increased storing ability of breads made with sourdough. This last is due to the correlation between the pH of a bread and its keeping quality. That is, as the pH decreases, the level of acidity increases, and the higher acidity in turn contributes to the increased life span of the loaf. Sourdough therefore provides the benefits of good eating quality, increased nutrition, good leavening ability, and good keeping quality. This commonplace miracle of nature has been of incalculable value over the centuries in lands where bread was the primary foodstuff and, being baked but once every three or four weeks, needed to be stored for lengthy periods.
Rye flour in Germany is categorized by its ash content. That is, a sample of flour is incinerated, the charred remains, or “ash,” is weighed, and the flour is labeled according to the percentage of ash it contains. The ash is almost all minerals, and the higher the percentage, the more whole is the flour. In this way, Type 610 rye flour contains .61 percent ash (in the United States, Type 610 would be labeled white rye), while Type 1740 has 1.74 percent ash (whole rye in the United States); in between are numerous gradations, each signifying ash content and the relative lightness or darkness of the flour. The amount of ash correlates to the degree of extraction; Type 610 is about 60 percent extraction, with Type 1740 being close to 95 percent extraction. Beyond these gradations of rye flour, there is another German category called Schrot, which is a form of chopped grain. It is available in a number of degrees of coarseness, referred to as fein, mittel, or gross (fine, medium, or coarse).
In the United States, the baker has access to quite a diminished array of rye flours, usually sold only as white, medium, dark, and whole. Extraction rates, ash content, and protein quantity are lowest in white rye and highest in whole rye. White rye flour has little in the way of flavor or color, and is generally a poor choice in bread making. Medium rye is substantially better, producing breads with better nutritional value and more flavor. And whole-rye flour is better yet in terms of flavor and food value (it is the rye flour of choice for most of the formulas in this book). Dark rye is the flour milled from the periphery of the grain, similar to the clear flour produced during the milling of wheat. It tends to be coarse and sandy, to absorb quite a lot of water, and in general is difficult to work with.
Pumpernickel rye, often called rye meal, is just that: a coarse meal rather than a flour; it is made by milling the entire rye berry. It can substitute for whole-rye flour, the main difference being the mealy consistency of pumpernickel. In any event, pumpernickel means that the entire berry has been ground, and from a milling perspective does not have anything to do with the artificially black breads known in the United States as pumpernickel. Filling out the rye list are rye chops (similar to the German Schrot in that the rye berry is chopped rather than ground), cracked rye, and whole rye berries. Although the rye spectrum available to American bakers is not quite as broad as that enjoyed by European bakers, we nevertheless have sufficient variety at our disposal to make breads of first-class character and quality.
Chapter 6, Sourdough Rye Breads, has more information on the unique requirements of rye, from mixing and handling through baking and eating.