- Summer 1999 "Update" Newsletter Article -
Research shows promise for new resin applications
Copyright © 1999. All rights reserved.
New approaches to wine filtration tested by a Fresno State chemistry professor have shown that synthetic resins could be the next agent commonly used by wineries to clarify wines. Positive results in earlier tests prompted Professor Barry Gump and graduate student Joyce Huang to increase volumes of grape juice and white wines in the testing of three resins for protein and polyphenol removal.
Unstable proteins are the most common factor in the formation of haze in juice or wine, Gump writes in a new research report published by the California Agricultural Technology Institute (CATI). And since color and clarity are key factors in a wine’s attractiveness to the consumer, the issue of haze formation is of critical importance to any winemaker, he noted.
"Unstable protein can be removed by a variety of methods," Gump said. The general process is called "fining." The most common fining method is to mix a natural clay called bentonite in batches of wine. The bentonite absorbs proteins and other molecules which can lead to haze formation.
Unfortunately for the wine industry, new environmental safety regulations are making it more costly to deal with the relatively large amounts of solid waste material produced through the bentonite fining method.
"Wineries can distill the alcohol content out of lees. In the past, the solid waste would go back into the vineyard, as fertilizer," Gump noted. "Now anything containing alcohol is considered a hazardous waste and needs to be specially disposed."
Adsorbent resins are already used by the food industry for a variety of tasks, including to stabilize and decolorize sugar juices. "They are promising materials for replacing bentonite in the fining process," Gump said.
Tests conducted at the Viticulture and Enology Research Center (VERC), with support from CATI and the American Vineyard Foundation, focused on three commercially available resins. Wine and juice samples were pumped slowly through columns of resin, then heated and analyzed for haze formation, as well as for protein and phenolic content. Levels of pH, *brix, titratable acidity and metals also were measured.
All three resins were found to have "effectively stabilized the grape juices and wine," the authors found. Resin treatments did not affect pH or titratible acidity levels in the juices or wine, and the sugar content of the grape juice also was unchanged.
Sensory evaluations by a trained panel of wine tasters were conducted to compare the three resin-treated wines with a control sample of untreated wine and a sample filtered by conventional bentonite methods. While the control sample was ranked highest by the panel, one of the resin-treated samples ranked second and above the bentonite-treated sample. This "shows promise for resin applications in the juice and wine industries," the authors conclude.
Details of this experiment, including tables and charts of specific results, are contained in the new publication, entitled "Removal of Unstable Protein in Grape Juice and Wine by Adsorbent Resins." It is available for viewing on the CATI Internet web site. Single hard copies also may be ordered by using the publications order form on Page 7.
{ page top }