Wine quality is often hampered by adverse weather conditions or incorrect fermentation procedures. Cold or rainy weather during the grape ripening produces musts with low sugar content so that wines with low alcohol level and poor taste are obtained. In this case reverse osmosis, nanofiltration or osmotic distillation can be successfully applied to the must concentration before fermentation in order to improve the wine quality. Conversely, sunny growing seasons in warm climate produce grapes with high sugar level. The wines are characterised by robust flavours and taste, but the alcohol content is often too high for many consumers. The problem can be circumvented by harvesting less ripe grapes, however this compromises the flavours these wines have been appreciated for. The partial removal of ethanol from bulk wine to adjust the alcohol level has become a preferred technique. This allows the winemaker to harvest the grapes at full ripeness, with all the benefits of enhanced flavour intensity and no problems about ethanol content. An additional frequent problem in wine making is the volatile acidity. Occasional spoilage or stuck fermentation result in poor quality and, for values exceeding 1g/L acetic acid, in the total loss of the production. Membrane contactors can be used to improve the wine quality when needed. In order to remove ethanol the wine is passed through a porous hydrophobic membrane and pure water is passed along the other side. The vapour pressure difference across the membrane gives rise to the diffusion of alcohol vapours towards the water side. Fig. 1 shows the results obtained by four membranes. The removal of volatile acidity from wine was performed by coupling the membrane module and an ion exchange column: a low volume of water was circulated in a closed loop downstream the membrane and rapidly saturated with respect to ethanol and other volatile compounds of the wine whereas only acetic acid was continuously removed. A mathematical model of the processes investigated is also presented. Reasonable flow sheets of the processes are developed and discussed both for alcohol adjustment and for high ethanol removal (production of low alcohol wines or alcohol free wines) as well as for volatile acidity removal. Finally the method is compared with existing technologies (stripping and reverse osmosis).
Membrane Contactors in Wine Processing / Bruni L.; Gostoli C.. - ELETTRONICO. - (2007), pp. 1-4. (Intervento presentato al convegno PERMEA 2007, Membrane Science and Technology Conference of Visegrad Countries tenutosi a Siofok , H nel 2-6 Settembre 2007).
Membrane Contactors in Wine Processing
BRUNI, LUIGI;GOSTOLI, CARLO
2007
Abstract
Wine quality is often hampered by adverse weather conditions or incorrect fermentation procedures. Cold or rainy weather during the grape ripening produces musts with low sugar content so that wines with low alcohol level and poor taste are obtained. In this case reverse osmosis, nanofiltration or osmotic distillation can be successfully applied to the must concentration before fermentation in order to improve the wine quality. Conversely, sunny growing seasons in warm climate produce grapes with high sugar level. The wines are characterised by robust flavours and taste, but the alcohol content is often too high for many consumers. The problem can be circumvented by harvesting less ripe grapes, however this compromises the flavours these wines have been appreciated for. The partial removal of ethanol from bulk wine to adjust the alcohol level has become a preferred technique. This allows the winemaker to harvest the grapes at full ripeness, with all the benefits of enhanced flavour intensity and no problems about ethanol content. An additional frequent problem in wine making is the volatile acidity. Occasional spoilage or stuck fermentation result in poor quality and, for values exceeding 1g/L acetic acid, in the total loss of the production. Membrane contactors can be used to improve the wine quality when needed. In order to remove ethanol the wine is passed through a porous hydrophobic membrane and pure water is passed along the other side. The vapour pressure difference across the membrane gives rise to the diffusion of alcohol vapours towards the water side. Fig. 1 shows the results obtained by four membranes. The removal of volatile acidity from wine was performed by coupling the membrane module and an ion exchange column: a low volume of water was circulated in a closed loop downstream the membrane and rapidly saturated with respect to ethanol and other volatile compounds of the wine whereas only acetic acid was continuously removed. A mathematical model of the processes investigated is also presented. Reasonable flow sheets of the processes are developed and discussed both for alcohol adjustment and for high ethanol removal (production of low alcohol wines or alcohol free wines) as well as for volatile acidity removal. Finally the method is compared with existing technologies (stripping and reverse osmosis).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
