Rye bread is a general category of bread containing various percentages of rye flour. Pumpernickel is a type of dark rye bread. Traditional European pumpernickel bread is made only with dark rye flour and sometimes rye berries and does not contain wheat flour. While wheat flour contains both glutenin and gliaden, rye flour only contains gliaden. That makes traditional pumpernickel more gummy and it lacks the elastic structure needed to trap the air produced by the yeast during fermentation. Traditional pumpernickel is, therefore, more dense.