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Research
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Chemical engineering aspects of winemaking operations include studies of fermentation and reaction kinetics, crystallization, immobilized enzymes and cells, distillation, solute adsorption, membrane separations, and process modelling.
There are several aspects of wine fermentations, such as high initial levels of both glucose and fructose, final ethanol concentrations of 120 g/L, and significant cell death, which are not described by most models for alcoholic fermentation. Our studies focus on the substrate selectivity and death kinetics of wine yeast strains and data are interpreted with an existing wine fermentation model and the use of parameter estimation routines. On-line measurements of wine fermentations with very sensitive pressure transducers are in progress with subsequent parameter estimation for temperature and rate control.
Studies of the oxidation of gallic and caffeic acids, the formation of hydroxymethyl furfural, the binding of bisulfite to carbonyls, the cleavage of disulfides by sulfite, and the reaction of isocyanate with ethanol are of importance in wine aging and storage. The work is complicated by the need to measure low concentrations of often volatile components in the wine matrix by gas and liquid chromatographic methods. The kinetics constants are evaluated by nonlinear parameter estimation by using the modified Gauss-Newton and Davidson-Fletcher Powell methods.
The precipitation of potassium bitartrate and, to a lesser extent, calcium tartrate from wine are common physical instabilities. Wines are generally exposed to low temperatures in order to encourage the precipitation of these salts. Our studies involve the analysis of batch crystallization kinetics for the design of continuous, dense bed crystallizers and the development of rapid stability tests.
The modeling and advanced control of distillation columns for the production of brandies and whiskeys is based on the behavior of trace volatile components instead of the major components, water and ethanol. Multistage, multicomponent models for columns with multiple feeds and sidedraws have been developed for this, based on the volatility of ten of the more important trace components.
The use of natural products such as egg and milk proteins for the reduction of tannin in red wines is an example of batch solute adsorption as practiced in winemaking. There is a long-term effort in our group to find improved and alternative heterogeneous adsorbents that can be regenerated to minimize residues in the wine and solid waste disposal.
The batch delivery and processing of loads of grapes which are kept separate according to their type and source can be well described by event-driven simulation models. The continued development of such models, applicable to almost any winery size and type, is in progress. A PC-based simulation program is being used for the evaluation of winery designs, grape delivery schedules, and daily planning during the harvest.
Current research projects include the investigation of factors affecting the formation of hydrogen sulfide during wine fermentations; design and evaluation of a fluidized bed crystallizer for the recovery of tartrate salts from wines; reaction of hydrogen sulfide in model solutions and wines; and the determination of free sulfur dioxide in wine by capillary electrophoresis.
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Support
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| American Vineyard Foundation Industry |
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