Suisun Valley Grape Growers Association is currently in the early stages of having Paul Skinner, the preeminent authority of terroir definition, work with them. As SVGGA’s publicist, this allows me to have more immediate access to Paul and his high-tech consulting firm Terra Spase.

[SNAPSHOT OF PAUL SKINNER: Ph.D. of Vineyard Investigations to offer GIS solution oriented consulting services to vineyard owners and wineries, Paul’s unique array of spatial information products include a powerful set of in-house tools and services which combine soil, weather, vine and wine data with statistical analysis, forecasting, and mapping tools.]

So, as the fires raged close to my neighborhood and in the Suisun Valley’s hills, I couldn’t help but wonder, “Are these grapes going to be picking up the flavors of the dust particles that are blanketing our atmosphere?” This has become (no pun intended) a hot topic, with even our Bay Area TV stations picking up the story. I called Paul, and he presented very interesting answers, as I would have imagined, and should be very helpful to anyone who grows grapes under these current fiery conditions.

The answer is, “Yes, if viticulturists don’t do something about it.” Unlike what the news has been carrying, which pretty much has to do with filtering wines, Paul presented the results of Investigations conducted during 2003 and 2004 into the nature and amelioration of taints in grapes and wine, caused by smoke resulting from bushfires. Authors of this report were Peter Godden, Ella Robinson, Leigh Francis, Kate Lattey, Geoff Cowey, and David Boehm from the Australian Wine Research Institute (AWRI), based in South Australia.

The above link will take you to the entire study. This paragraph begins to tell the importance of doing something, “The investigations, while by no means definitive in nature, indicated that exposure of grapes to bushfire smoke as early as veraison may cause levels of taint in the resulting wine which substantially reduces its commercial value. It is apparent that the taint compounds are present within the grape skin, and thus their extraction is difficult to avoid during winemaking, especially red-winemaking where extended skin contact is necessary. For white wines, winemaking treatments that minimize contact between juice and skin may be beneficial in reducing the intensity of any taint.”

Paul cited to the Suisun Valley board of directors that unlike filtration – not to negate filtration efforts – washing grape vines and leaves as soon as possible is an important step to keep the guaiacol concentration (“smoky” taint) in grapes and wine to a minimum – if at all present in minuscule amounts.

Interestingly, machine harvested fruit seems to be more impacted. Paul Skinner cited that that may be due to more leaves being involved in machine harvesting; therefore, there’s more contact with leaves that have residue on them. The grape growers stated that most of the machine harvesting they’ve seen takes the fruit from the rachus (part of the cluster that holds the berries in place) and keeps most leaves, stems, and rachus still on the vine after the fruit’s been harvested. Everyone, including Paul, was in agreement with this.

According to Skinner, regarding samples collected and analyzed from washed fruit in the study, “While it was obvious that some of them contained particulate matter, little or no guaiacol was detected in them. The Ovens Research Station (Department of Primary Industries, Victoria) examined bunches and leaves from the trial and ascertained that approximately 90% of ash and particulate matter had been washed off the grapes by the water washing treatments.”

These treatments included the following trials:

  • Cold water
  • Cold water plus wetting agent
  • Warm water, approximately 25° C (77° F) when contacting the fruit
  • Cold water + 5% ethanol
  • Milk

According to Terra Spase, “Washing grapes in vineyards seems all important in areas that are heavily influenced by the California fires. If machine harvesting is a necessity, leaf plucking followed by a high-volume, high-pressure cold water wash in the vineyard, and minimizing leaf matter entering the fruit bins during harvest should be employed.”

Paul Skinner can be reached at 707-967-8325, if you need further help with your vineyard this year, or a better understanding of how the 2008 vintage is going to be challenged.