Rye flour

Rye flours differ from wheat flours in the type of gluten they contain, and an open Canadian baking textbook notes that rye dough traps little of the gas the yeast produces. For that reason, starch and pentosans, rather than gluten, give a rye loaf its structure.

Pentosans are gummy carbohydrates that swell when moistened and help give rye loaves their cohesiveness. Rye flour has greater water binding capability than wheat flour, because of its starch and pentosan content, so rye doughs are sticky and the crumb stays moist and dense.

The grade of extraction matters too: higher extraction flours have more ash, fiber and pentosans and less starch, which means darker flour with a stronger flavor. Because rye does not need to be aged as much as wheat flour, the textbook suggests it is good for about three weeks after milling when stored dry. Bakers often blend rye with wheat flour to get lift as well as flavor.