Conference Explores Science of Wine Terroir

Speakers at U.C. Davis say science supports link between climate and wine quality, but not soil-minerality link

by Jon Tourney
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Geologist Alex Maltman and climatologist Greg Jones discuss science and wine terroir at the Robert Mondavi Institute's Terroir 2012 conference in Davis, Calif.
Davis, Calif.—Exploring the topic “What Science Does and Doesn’t Tell Us about Terroir,” last week’s Terroir 2012 conference presented by the Robert Mondavi Institute (RMI) at the University of California, Davis, indicated that science shows terroir and wine character are more directly linked to climate than to soils or other vineyard site factors.

A panel session “New Research on the Terroir of Wine” included scientists who discussed terroir in relation to their studies in geology and climatology, and winemakers who discussed terroir based on their experiences with grapegrowing and winemaking.

Minerality in wine unsupported by science
Alex Maltman, professor of earth sciences at the University of Wales in Aberystwyth, U.K., and a grapegrower and winemaker, has published articles and lectured on the role of geology in wine, beer and whisky.  Maltman is known for his observation that science does not support the concept of “minerality” in wine. He said the term minerality, as a wine descriptor, is relatively new, but it has “exploded in the popular wine press (particularly over the past 10-15 years) and is now one of the most widely used wine descriptors.”

Maltman said, “It has taken off because it’s attractive, and it’s good from a marketing standpoint, but from a science standpoint it doesn’t really work like that.” He acknowledged that grapes grown in different locations have different soils and geological substrates, and they can produce wines with different characteristics. The idea that vines can absorb soil minerals and elements unique to their site may seem logical on the surface, but in reality the process is much more complex and difficult to predict or prove. Maltman explained that rocks and soil must undergo reactions, often water-driven, for elemental particles to become soluble. They would then have to be transported to a vine’s roots before being transported into various parts of the grapevine. Assuming these mineral elements make it into the grapes, they would then go through fermentation and other wine-processing operations that would likely offset or mask any character the minerals could have.

Maltman concluded, “Any minerals that could make it into the wine are in amounts too small to be tasted, and they are pretty much tasteless anyway.” He explained that inorganic minerals are non-aromatic. He also noted that there is no mention of minerals or minerality in the most commonly used reference books about wine flavor chemistry.

Since published articles in the past have erroneously reported Maltman “debunking” the concept of terroir, he was clear in stating, “I’m not saying that vineyard soils, minerals and geology are unimportant in vineyards, nor am I debunking terroir. But the connection between vineyard geology and wine character has to be very indirect, and it’s very complex, with no literal, direct connection.” He summarized, “Whatever minerality is, it is not the taste of vineyard minerals.

“The term minerality is now entrenched, so it’s too late to turn back the tide, but the term should be used as a metaphor, not as something directly derived from soil minerals where the vine is located.”

In a panel discussion later in the day, conference speakers were asked what research they would like to see regarding terroir. Maltman suggested a project that would collect soil types from different locations, place the soils in separate but uniform containers, then plant grapevines in each soil type with all vines in a greenhouse with the same growing conditions.  “Having all vines growing in the same environment, we could then make wines and see if there are differences specifically due to different soil types,” Maltman suggested.

Climate data can define, identify vineyard terroir
Dr. Greg Jones, professor and research climatologist in the Department of Environmental Studies at Southern Oregon University, admitted his bias as a climatologist, but stated, “Geology is important in terroir, but not as important as climate.” Jones has done research and consulted on projects globally to look at spatial climate data to better define wine regions and determine the varieties best suited to plant in specific sites. Of the major factors influencing wine character and quality, Jones believes the grape variety is the most important factor, followed by climate, then landscape and soil.

Jones observed, “Some vineyards consistently produce fine wine, but when the weather is just right during the growing season, these sites produce exceptional wine, and those vintage differences have nothing to do with the soil.” He also listed characteristics associated with wines grown in each of three major types of growing climates: cool climates, intermediate to warm climates, and warm to hot climates. He said, “Grapes grown in these three types of climates each produce common wine characteristics within each climate category.”

Referencing other wine-related research, Jones said science to date has identified about 400 aromatic compounds in wine. Most of these result from fermentation and yeasts, or from the grape variety, not from soils and geology.

Jones advocated for better spatial climate data worldwide, which will be useful for all scientists and human activity, useful for making decisions in agriculture and development, and useful for long-term planning for climate change. Jones summarized: Viticulture and wine production are extremely environmentally sensitive. Finding the best terroir requires spatially appropriate data in all forms, which is becoming more available. Understanding climate structure differences between locations helps define cultivar suitability for planting, and wine style and quality.

The human aspects of terroir
Napa Valley winemaker Andy Erickson, a consulting winemaker and co-owner of Favia Wines took a more philosophical approach saying, “Terroir is a cultural term, not a scientific term. It’s something we can debate. It’s an idea and a concept, not something to be proved or disproved.” He acknowledged that terroir involves geography, geology, climate and people. He focused on the people aspect of terroir. “My job as a winemaker is to maximize terroir,” he said. He listed the human factors and practices he feels are important to maximize terroir: variety choice, clone and rootstock; organic farming (better expresses site with lower inputs); water management; canopy management; crop load; harvest date/parameters; add yeast or allow native yeast fermentation, and clean winery practices. Erickson observed, “As a purist, I like to use native yeast for fermentation. I think it allows the wine to better express the fruit from the vineyard.”

The RMI conference also included academic and industry experts speaking about terroir in relation to other foods and beverages such as cheese, tea and oysters. In the conference’s final session, panelists debated whether or not terroir should be more clearly defined in order to establish parameters to differentiate products. One argument was that without a definition, terroir is mostly a marketing term rather than based on facts. Although defining terroir may provide more consistency for its use, society also tends to dislike standardization and regulation that could occur. Most agreed that the terroir concept has more value today, as more consumers are moving beyond mass-produced and processed foods with a growing interest in products with unique origin and geographic variation.

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