ABSTRACT
A main disadvantage of macroscopically homogeneous, hard food products is that they are very difficult to break down by biting and chewing during mastication. The fracture stress of such products will be of the same order as that of the teeth or higher, so we can eat them only when they dissolve readily in the mouth or if they contain large inhomogeneities. The latter is the case in hard cellular solids such as biscuits and toast, where the sponge structure allows them to be broken down easily during mastication. Small pieces of hard solids will, in general, readily dissolve or contain large enough structural defects that humans can fracture them between the teeth (e.g., sugar crystals). Hard sweet candies are usually kept in the mouth and left to dissolve. Products such as dark chocolate bars consisting of cocoa solids and butter and sugar are not homogeneous solids because of the presence of some uncrystallized cocoa butter and amorphous and crystallized sugar. These products contain large inherent defects, which allow humans to bite a piece of a chocolate bar without endangering their teeth.
