Jacob ben Asher thought that washing the mouth was not sufficient to remove all residue of cheese, and suggested that eating some additional solid food is required to clean the mouth.[106] Hard and aged cheese has long been rabbinically considered to need extra precaution,[107] on the basis that it might have a much stronger and longer lasting taste;[108] the risk of it leaving a fattier residue has more recently been raised as a concern.[109] According to these rabbinic opinions, the same precautions (including a pause of up to six hours) apply to eating hard cheese before meat as apply to eating meat in a meal when the meat is eaten first. Judah ben Simeon, a 17th-century physician in Frankfurt, argued that hard cheese is not problematic if melted.[110] Binyomin Forst argues that leniency is proper only for cooked cheese dishes and not dishes topped with cheese.[111]