The foam stability is one of the most important criteria to evaluate the quality of green draft beer.The fact that Lipid Transfer Protein 1(LTP1) is a kind of most important beer foam promoting protein fraction in beer has been proved.Proteinase A is a product of yeast Saccharomyces cerevisiae cells,encoded by PEP4 gene in yeast S.cerevisiae genome,the degradation of LTP1 by proteinase A could lead to the decline of beer foam stabilization in green draft beer