A German ligature that originally stood for 'sz', but can be transliterated as 'ss'. It is never found in Swiss German. It looks like a B, but sounds like an S. Compare to the boring language known as English, which only has the ligatures Ã and Å, which are rarely used.
The only other flour used in traditional pumpernickel is wheat flour, which is used as an ingredient in the sourdough starter, a pre-fermented flour, water and yeast mixture that combines with the rye flour to hold the bread together.
This is the same reason that hard wheat flour is added to whole wheat and rye flours for bread. Soft wheat flours, from soft red winter wheat and white winter wheat are sold for family use for biscuit or cake flours. In commercial production it is used for crackers, cakes, cookies, and pastries.