Rye flour

One US cup of rye flour weighs 106 grams. Going the other way, 100 grams is about 0.94 cups.

Rye flour is milled from rye grain (Secale cereale), a hardy cereal grown widely in northern and eastern Europe where it thrives in colder soils than wheat tolerates. It is the traditional flour for pumpernickel, black bread, Scandinavian crispbreads, and much of central European rye baking. In American baking it appears most often in rye bread and Scandinavian-style crackers, and less often as a substitute for a portion of wheat flour in muffins and pancakes for a distinctive nutty flavour.

USDA FoodData Central publishes rye flour in three separate grades based on how much of the grain is retained:

- Light rye (FDC 168887) is essentially just the endosperm — the bran and germ removed. It behaves closest to all-purpose flour in colour and rise. - Medium rye (FDC 168886, this entry) is a middle grind that retains some bran and germ, producing a slightly tan colour and a fuller flavour. It is the most common commercial rye flour in the United States. - Dark rye (FDC 168885) retains most of the bran and germ, is dark tan to grey-brown, and has the strongest flavour. It is heavier per cup (about 128 grams versus 102 to 106 for medium and light) because the bran adds density.

King Arthur's chart publishes 'Medium Rye Flour', 'White Rye Flour' and 'Rye Flour Blend' all at 106 grams per cup. This is likely a rounded common figure across their retail products rather than a distinct measurement for each. The USDA figures show more variation across grades, with the pattern that darker rye is heavier per cup — the opposite of what one might expect, and driven by the fact that bran has higher bulk density than pure endosperm when milled to the same grind coarseness.

Rye differs from wheat in a way that matters for baking. Rye has less gluten and much more pentosan (a class of soluble fibre that absorbs several times its weight in water). A 100 percent rye dough is very sticky and dense compared with a wheat dough; the gluten structure that gives wheat bread its rise is largely absent, and rye breads rely instead on the pentosans to trap gas from fermentation. This is why traditional rye bread is dense and moist rather than airy, and why most 'rye bread' sold in American supermarkets is actually mostly wheat flour with a smaller proportion of rye for flavour and colour.

Related products this entry does not cover: pumpernickel flour, which is coarsely ground whole-grain rye (essentially dark rye ground more coarsely, sometimes with cracked rye berries included); rye chops and rye flakes, which are cracked or rolled whole rye grains used for hot cereal and multigrain bread inclusions (KA lists these separately at 120 and 124 grams per cup respectively); rye berries, the whole intact grain used for pilaf-style dishes; and rye malt, an ingredient in beer brewing rather than baking. Triticale flour is a hybrid of wheat and rye and measures between the two.

FDA identity standards for rye flour are addressed under 21 CFR Part 137 (cereal flours), which covers grade definitions and enrichment options. Codex Alimentarius does not have a specific rye flour standard; rye is covered under the general standard for cereals.

The category here is 'milled' because rye flour behaves like other fine milled powders in a measuring cup — it clumps, bridges over air pockets, and its density depends on scoop method. The 10 percent tolerance applies. Both sources sit well inside it.