While wheat flour predominates in the breads of southern Europe and the UK, rye flour plays a more important role in the breads of northern and eastern Europe. This is due to rye's superior ability to grow in the poorer soils and cooler, wetter climates of those regions.
Chemical differences in the proteins and enzymes found in rye present differences in how rye flour behaves when mixed with water to make dough, and these differences impact the use of pre-ferments, mixing, fermentation and baking when there is more rye than wheat flour in the dough.
There are a number of different types of rye products available. They vary in how much of the rye berry is included, just as whole wheat differs from white wheat flour. They also differ in how finely ground the rye is.
There are breads made with 100% rye flour, but many other breads are made with lesser percentages. The influence of rye flour on dough handling and on the resulting taste and texture of the bread varies according to the proportion of rye used.
Chemical differences in rye
Gluten is the primary protein found in wheat, and the methods of mixing dough made with wheat flour center on their impact on gluten development and structure. Gluten forms the framework of cells that trap the carbon dioxide generated by fermentation of sugar by yeast. This trapping generates the expansion of the dough (rising) and ultimately the texture of the bread's crumb.
Rye contains much less gluten than wheat, and the gluten rye contains is of poor quality when it comes to trapping air bubbles. Consequently, breads made with mostly rye flour do not expand as much as those made with mostly wheat flour. The crumb of breads in which rye predominates tends to be dense with smaller holes. On the other hand, rye has more free sugars than wheat, so rye dough ferments faster.
Rye contains a group of important complex sugars called “pentosans.” These are present in other grains, but rye has more of this substance. Pentosans are important to the baker for several reasons. They compete with the proteins that make gluten for water, and water is the substance that leads the proteins to combine to form gluten. This means that rye doughs often require a higher proportion of water than doughs in which wheat predominates. Pentosans break apart easily during mixing, and their fragments result in a stickier dough. Because of this, rye doughs require gentler and, usually, briefer mixing than wheat doughs.
Rye is higher in the enzymes (amylases) that break down starch into sugars. Starch is needed to form the structure of the crumb, and if too much starch is split up, the texture of the bread suffers and becomes gummy. Traditionally, this is prevented by acidifying the rye dough, which slows down the action of amylases. This is why breads with a high percentage of rye flour are made with rye sour (rye-based sourdough starter), even if commercial yeast is added.
Acidification of rye dough has other nutritional advantages specific to rye bread which may also be of interest to the home baker, as well as the advantages that also apply to wheat-based sourdoughs.
Rye products used in baking bread
Whole rye berries may be used in bread, after soaking, to contribute flavor and texture. Rye berries are also used after breaking them into smaller pieces in the form of rye chops, cracked rye, rye flakes, and so forth.
The rye flours you may find include the following:
In Europe, especially Northern Europe, a much wider range of rye flours is available, encompassing different grinds as well as a variety of percentages of bran and germ.
Rye flour that contains the oily germ (pumpernickel, dark and medium) spoils very quickly, so try to buy the freshest possible and store it in the freezer.
Rye flour used together with wheat flour
A small amount of rye – 5-10% of the total flour by weight – has a definite effect on the flavor of the bread. The distinctive flavor of the rye itself may not be noticed, yet the bread's overall flavor seems better. This may be due to the action of the amylases in rye releasing more sugars. This small addition of rye is what defines a French pain de campagne. These breads are often sourdoughs, but the rye may be added with the rest of the flour rather than as a rye sour. There is so little rye in the dough, that it's behavior during mixing and fermentation and its texture when baked may be indistinguishable from a purely wheat bread.
Breads containing up to 40% rye flour are usually called “rye bread.” Jewish Sour Rye (New York Rye, Deli Rye) is a familiar example. The rye flour is in a large enough proportion so that it is advisable to add all or most of it as a rye sour. There is enough rye so that a distinct rye flavor is tasted. However, there is enough wheat flour to provide gluten to form the kind of crumb we associate with wheat breads.
The dough in these breads will feel different during mixing, tending to be stickier. The temptation is to add more flour, but this should be resisted. When hand kneading sticky rye doughs, using rapid, light strokes - minimizing the time your hands are in contact with the dough - decreases the amount of dough that will stick to your hands. You may also find that wetting your hands with water or lightly oiling them helps.
Breads with over 50% rye flour are another story. All the special considerations due to the chemical differences in rye become more important as the proportion of rye increases. Typically, these breads have a short bulk rise and, once baked, should be allowed to rest for several hours before slicing, so the crumb can set up properly. In the case of breads with 70% rye or more, a rest of 24 hours, even up to a couple of days, may be required.