Will mold grow faster on rye bread or pumpernickel bread?

Mold grows best on rye bread.

Mold requires certain conditions to grow: a food source, moisture, oxygen, and a warm environment. Rye bread and pumpernickel bread both provide a food source and moisture, but rye bread has a higher acidity level than pumpernickel bread. Mold thrives in acidic environments, so it will grow faster on rye bread. Additionally, rye bread typically contains more moisture than pumpernickel bread, which also contributes to the faster mold growth.