The grain used in biogas production is generally coarse grain. However, the anaerobic digestion of coarse grain often leads to excessive foam formation in biogas reactors. Comprehensive foaming experiments using six sample grain species, namely, triticale, wheat, rye, barley, oats, and millet, were carried out in order to investigate the reasons for grain-based foam formation and to develop methods for minimizing foaming problems. It was found that the intensity of foam formation depended not only on the grain species, but also on the processing of the coarse grain: the finer the grain was ground, the higher the foam content in the test bottles. The most intensive foam formation was observed for wheat and triticale. The addition of soybean oil to coarse grain led to a reduction in foam intensity.