rye flour
Flour milled from rye, robust and slightly sour in flavour, the basis of dark Nordic breads.
In German-speaking countries rye flour is in every supermarket; in English-speaking ones it is more often found in health food shops, Eastern European grocers or by mail order. It forms almost no gluten structure, so pure rye doughs are usually made with sourdough and stay dense and moist.
Substitute:
Wholemeal wheat or wholegrain spelt flour come closest in flavour but give a lighter, milder result, and for pure rye breads there is no real substitute, because wheat behaves fundamentally differently in the dough.