The Research On Efficient Secondary Fermentation Of Beer

Beer has been industrial produced in China over one hundred years.Through the rapid development in recent decades,China has become the largest producer of beer around the globe.As we all know,during the beer brewing process,diacetyl and non-biological stability?cold haze?are two critical factors that can restrict storage time,quality,and stability of the finished beer products.In this paper,the continuous heat treatment was applied to treat beer post-fermentation liquid,accelerate the decarboxylation of ?-acetyl lactic acids?diacetyl precursor?into diacetyl.The fermentation liquid after heat treatment was cooled down to make diacetyl reduced into 2,3-butanediol,keep the TVDK content of finished beer in the low level,inhibit the recovery of diacetyl.In the meantime,low temperature storage at-3? was used to accelerate the precipitates of the sensitive polyphenols,sensitive proteins in the green beer,and ensure the non-biological stability of finished beer.The main research results are reported as following:?1?According to the studies of equipment and technical parameters of pilot trial continuous post-fermentation,the optimum condition of heat treatment for beer postfermentation liquid required temperature of 77? and treatment time of 20 min.Under the optimum condition,the ?-acetyl lactic acids,which is the precursor of the diacetyl,could be transformed into diacetyl to make the TVDK in finished beer at low content level.In this way,the increasing of diacetyl in the finished beer was able to be inhibited effectively.The studies also found that the heat treatment had no significant effects on TBA value,ethanol,ethanol,isobutanol,isoamylol,and other volatile subtances?p > 0.05?.?2?The immobilized yeast was applied into the continuous post-fermentation;the residence time of post-fermentation liquid staying in the packed bed reactor was extended longer.As the results,the TVDK content of post-fermentation liquid decreased firstly then increased,and reached the minimum value at 2.75 h.?3?The green beer was stored at-3-0?.the sensitive polyphenols,proteins,and cold hazes could precipitate more quickly with the temperature being lower.The kinetic equations of these compounds were:Sensitive Polyphenol Precipitate: K=7×10¹⁸e^-0.162/T?R²=0.968?Sensitive Protein Precipitate: K=3×10²⁹e^-0.249/T?R²=0.9718?Cold Haze Precipitate: K=1×10²⁰e^-0.168/T?R²=0.935??4?The finished beer had no significant changes in physiochemical indexes,sensory indexes,and the contents of flavor compounds under the optimum heat treatment condition?77? and 20min?.Based on the cold haze precipitate kinetic equation,the cold haze precipitating at-2 to-3? had 1.5 times quicker rate and a third times shorter storage time than that at 0 to-1?.