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New wine research busts tannin additions myth
Friday, Jan. 27, 2012
By Brian Clark, College of Agricultural, Human and Natural Resource Sciences
Enologist Jim Harbertson, center, with research winemaker Richard Larsen, left, and
doctoral student Frederico Casassa.
doctoral student Frederico Casassa.
Downey said his and Harbertson’s research programs "are complementary rather than competitive.”
"The knowledge earned from scientific research doesn’t give you a competitive advantage,” he said. "Rather, it’s how growers and winemakers use that knowledge that gives the advantage.
"Working together actually achieves more for our respective industries,” he said. "By collaborating and sharing the load, the Washington industry gets more research outcomes for the same research dollar invested - and so do we.”
Indeed, Harbertson and Downey plan to continue their collaborative research. Among other things, they will be investigating the effects of aging red wines in oak barrels. The role of oak and oak’s contribution of tannins to wine quality is assumed but not well understood.
This and other questions have led the scientists’ respective institutions to sign a formal agreement, allowing them to collaborate over the long term in ways that would not otherwise be possible.
PROSSER, Wash. - If you’re using tannin additions in your red winemaking process, you may well be wasting your money, according to recently published research by Washington State University enologist Jim Harbertson and Australian wine and grape researcher Mark Downey of Victoria’s Department of Primary Industries.
Harbertson, Downey and colleagues analyzed commercially available tannin additives and found them to be, at best, an unnecessary expense for red wines made from Washington-grown grapes.
Many winemaking manuals recommend adding tannins in the belief that the additions help bolster mouth feel and improve color in red wine. A red wine’s mouth feel is the result of a range of chemicals causing astringency; it is described with a variety of words ranging from "velvety” to "drying.”
"At the recommended dosage, these additives are, at most, giving a slight tweak to astringency,” Harbertson said. "In higher doses, you get some aroma shifting and a negative impact on sensory character. It made them earthy tasting and turned the wine brown.”
Mouth feel differs from taste
Harbertson and Downey collaborated with renowned sensory scientist Hildegarde Heymann, professor of enology at the University of California-Davis, and her Italian post-doctoral student, Giuseppina Parpinello, to conduct sensory analyses of merlot and cabernet sauvignon wines made with tannin additions.
"In a collaboration with (Washington winery) Chateau Ste. Michelle, we added commercial tannin products to both barrel-aging merlot and to cabernet sauvignon after pressing the grapes,” Harbertson said. "We used a range of concentrations and a variety of commercially available additives to get a sense of what is going on when these products are added to Washington wines.”
Harbertson explained that there is a crucial difference between taste (flavor, aroma) and astringency, or mouth feel.
"Mouth feel is a tactile sensation,” he said. "It’s basically the removal of the lubricating proteins that naturally occur in the mouth. Aroma and flavor, in contrast, are receptor-based and are caused by our taste buds being stimulated by the flavor and aroma molecules in wine.
"Astringency is thought to be a result of chemical precipitation in which tannin molecules bind the lubricating proteins in the mouth, thus taking them out of action,” he said. "That’s why some wines have a drying or ‘spikey’ mouth feel, as the overabundance of tannins robs the mouth of its lubricants.”
Plenty of natural tannins
Not only did the additives have a limited or negative impact on wine quality, analysis of the products revealed them to be, at most, only 48 percent tannin.
"On the low end, we found some products to contain as little as 12 percent tannin,” Harbertson said. The products contain fillers that enable the additives to go into solution more easily.
"The bottom line for Washington red winemakers is this,” Harbertson said. "We have plenty of naturally available tannins in red grapes grown here. In an industry with tight margins and dealing with global competition, we are suggesting that the extra expense of adding tannins is simply unnecessary.”
White, ice wines might benefit
He speculated that tannin additions might control some problems faced by white wine makers, such as protein haze or botrytis fungus: "But this idea has not been scientifically tested,” he said.
Harbertson also mentioned that certain hybrid grape varieties, once grown in Europe for their resistance to diseases and pests, don’t produce much tannin on their own, so an additive is needed. However, most hybrids aren’t grown in Europe simply because they produce wine that is too acidic for most consumers.
Several hybrid varieties are still grown on the east coast of the U.S. and in Ontario, Canada, where they are popular as constituents of the ice wines enjoyed in the region.
The paper discussed in this article, "Impact of exogenous tannin additions on wine chemistry and wine sensory character,” will be published in the April 2012 issue of the journal Food Chemistry. The paper was published online Oct. 1; readers with access to a subscribing institution may access the paper by visiting http://bit.ly/wsutannins.