In many modern breweries, the fermenters are so large relative to the capacity of the brewhouse vessels that several brews of wort must be combined to make one fermentation batch. Fermenter filling and pitching procedures vary considerably, and it is known that differences in these procedures and in the time taken to complete them can affect the course of the fermentation process and the quality of the resulting beer. Experiments are described in which laboratory fermenters were filled with wort either all at once or in two half batches, three thirds or four quarter batches at intervals of 6 hours between portions. Pitching rates and aeration also varied, but all the pitching yeast was always added with the first portion of wort. The effects on yeast growth, attenuation rate, FAN consumption and the composition of the finished beer were recorded. The results indicate that it is essential to provide additional oxygen (in the form of aerated wort) between 10 and 14 hours after pitching, when the yeast undergoes its second budding, in order to optimize the fermentative performance of the yeast.
Keywords : aeration brewers' yeast fermentation fermenter filling growth performance time