Using Rye Flour in Sourdough
Sourdough rye bread is a traditional bread throughout the Scandinavian countries, many parts of Central Europe, and Germany. In his book, Nutrition and Physical Degeneration, Weston Price mentions the diet of the people in the Loetschental Valley of Switzerland consisting primarily of hearty rye bread and cheese. There is something wonderfully satisfying about a good loaf of tangy sourdough rye bread. Rye has a delicious and bold flavor.
The gluten in rye is inferior to that of wheat, making rye a little tricky to bake with at first. The gas-trapping capacity of rye is less than that of wheat, making it unstable when used by itself, so most bakers mix rye with wheat flour to give the dough more structure. As in all adventures with sourdough, practice makes perfect. You can produce a great loaf of rye bread by understanding some of the properties of the flour.
Rye flour contains pentosans, which are polysaccharides (chains of sugars) similar in structure to starches and cellulose. When mixed with water these pentosans soak up the liquid to form a viscous gas-trapping gum. This viscosity tends to make rye bread dense and somewhat flat. Since a successful loaf of bread depends on the viscosity as well as the elasticity of the dough, adding wheat flour (which contributes elasticity) helps to balance the two. Viscosity is affected by mechanical mixing, pH, temperature, and percentage of salt. It is best to knead rye breads by hand, so as to not over-knead. Rye is very hygroscopic (takes on and holds water), allowing rye bread to stay fresher longer than wheat bread.
Rye and wheat grains both contain amylase, the enzyme that breaks down starches. The structure of a loaf of baked bread comes from starch having been gelatinized by the presence of water and heat. This gelatinized starch is susceptible to the action of amylase. Rye amylase is more heat-stable than wheat amylase, so a loaf of bread made with predominantly rye flour tends to be flat from the action of the amylase on the starch.
Adding wheat flour to the dough gives the finished loaf more structure since more of the amylase has been inactivated, leaving more starch to gelatinize. The acidic pH of naturally fermented dough also helps to inhibit the action of rye amylase. That may be why all traditional rye breads are made from sourdough. The starch is protected from the amylase until all of the amylase has been inactivated by the baking process. Salt inhibits the action of amylase as well. Using too little salt will contribute to a flat loaf.
Wheat gluten retains gas in the loaf until it is about half baked, somewhere between 125° and 165°F. Most of the “oven-spring” (rapid rising of the dough) is completed by that point. Rye dough, on the other hand, loses much of its gas early in the baking cycle (about 95°F) so there will be little oven-spring in rye breads. If you want a loaf with lots of volume you will need to increase the amount of wheat flour in the dough.
What is the correct proportion of wheat to rye flour? That depends of what kind of loaf you want to make. If you are looking for a fairly light sandwich-type loaf, you might want to limit the rye flour to about 20% of the total flour. Most traditional German rye breads contain around 30% rye, but they also rely on the fermentation process to lower the pH and thus inhibit the action of amylase. One of the traditional European rye breads, Vollkornbrot, contains 100% coarse rye meal. It has very long leaven and fermentation times and produces heavy, dense, and chewy loaves. They are delicious, although not generally what the American palate is accustomed to.
Hopefully, now that you know a little more about the properties of rye, you’ll feel comfortable experimenting with sourdough rye bread until you find the loaf that is exactly right for you.
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