Pressure fermentation and wort carbonation.

Nielsen, H., Hoybye-Hanse, I., Ibaek, D., Kristensen, B.J. and Synnestvedt, K.

Abstract
Fermentation can be controlled by the physical parameters of temperature, time, pressure and agitation, by wort composition, temperature, oxygen and carbon dioxide contents and by yeast strain, concentration, pre-treatment and pitching conditions. Although fermentation temperature and carbon dioxide pressure are only 2 of the 12 variables listed above they can give effective control of fermentation, yeast growth and beer aroma. Following a survey of previous investigations on the effects of temperature and carbon dioxide pressure, the possible effects of increase of temperature and pressure which are usually applied together are outlined. Thus an increase of temperature from 12 to 16 degrees C and of pressure from 0.1 to 1.2 atmospheres gives no significant change in pH or colour, but yields less hydrogen sulphide and dimethyl sulphide in the growth phase and less diacetyl in the beer. However there is poorer head retention in the beer and decreased cell viability and greater autolysis in the yeast. As a variation in procedure, wort has been carbonated to 0.3% before fermentation. The wort is aerated to 8 mg/litre oxygen and fermented without pressure at 15 degrees C. A flocculent yeast was used and it was found that carbonation of wort delays fermentation and yeast reproduction without altering the total quantity of yeast produced. Wort carbonation can be used in conjunction with pressure fermentation and is less stressful to the yeast than pressure fermentation alone.
Keywords : beer carbonation carbon dioxide fermentation inhibition pressure quality Saccharomyces carlsbergensis wort yeast