Previous studies by the present authors and their colleagues (Tech. Q. Master Brew. Assoc. Am., 1992, 29(4), 122-126 and 1992, 29(4), 127-133) showed that the dissolved carbon dioxide content of fermenting wort, the rate at which it is liberated from solution and formed into bubbles, and the behaviour of the bubbles in the liquid all have significant effects on the fermentation process and the quality of the resulting beer. The present paper concerns the possibilities for controlling the formation and behaviour of carbon dioxide bubbles in fermenting wort as an aid to the control of the fermentation process. Normally, carbon dioxide bubbles do not form until the fermenting wort is supersaturated with carbon dioxide, but on the basis of the known physical laws governing the behaviour of gases in liquids in which the gases are soluble, the authors postulated that ultrasonic vibrations, which would increase bubbling by producing a cavitation effect, would reduce the dissolved carbon dioxide level from a supersaturated condition to the normal saturation point, while passing a stream of nitrogen gas bubbles through the fermenter might actually reduce the dissolved carbon dioxide concentration to less than the saturation level. Experiments are described which confirmed these predictions. It was also found that yeast growth, the rate of ester formation, the height of the foam head formed during fermentation and the effects of the concentration of certain constituents of the wort in the fermentation foam on the composition of the resulting beer can be controlled through these effects on carbon dioxide bubbling.
Keywords : carbon dioxide fermentation foam nitrogen process control solubility ultrasonic