Novel foam proteins, monoclonal antibodies specifically recognizing said proteins, a method for determining foam protein contents in beer samples by an immunoassay using said monoclonal antibodies, a method for determining head retention and head retention stability of beer, as well as a method for evaluating raw materials of beer and stabilizers for beer are disclosed. The novel foam proteins crucial for head retention of beer have molecular weights of about 40000 to about 48000 as determined by Western blot analysis.