The Collaborative International Dictionary of English v.0.48:

Press cake \Press cake\
   A cake of compressed substance, as: in gunpowder manufacture,
   the cake resulting from compressing the meal powder; in the
   treatment of coal tar, the pressed product at various stages
   of the process; or, in beet-sugar manufacture, the vegetable
   residue after the sugar juice has been expressed.
   [Webster 1913 Suppl.]