As the climate strains, wine complexity wanes

Wine professionals use the markers that differentiate grape varieties as
guideposts when assessing quality and style and/or when blind tasting. Wine enthusiasts relish the complexity of their favorite expressions, a factor that contributes significantly to their enjoyment.

Wine is one of the foods richest in volatile aroma compounds, linked to as
many as 1,000 of them. That said, only 80 or so—including the monoterpenols responsible for the floral notes in Muscat (among other varieties) or the thiols that impart passion fruit and grapefruit aromas
to Sauvignon Blanc—have been widely studied.

“Now the days of comparing a

glass of Northern Rhône Syrah to

a strip of peppered bacon appear

to be coming to an end.”

In fact, the molecule responsible for the pronounced peppery notes found
in several French grapes—including Syrah from the Northern Rhône; Gamay from Beaujolais; and Duras, Fer, Négrette, and Prunelard, grown in the southwest—was only recently discovered.

Until 2008, knowledge of the aromatic compounds that account for the varietal character of red wines, especially free compounds directly extracted from grapes,was limited to methoxypyrazines, the culprit responsible for undesirable green notes in Bordeaux varieties. The discovery in an Australian Syrah of rotundone, a sesquiterpene responsible for those peppery notes, shed new light on its sensory significance.

Rotundone had been hiding in plain sight; it had remained undetected by
researchers in not only wine but food products such as Piper nigrum, or black
pepper, which has more than 50 volatile compounds. These researchers speculate that several factors complicated its detection, including the fact that 1) the molecule appears late during sensory evaluation sessions, when judges no longer expect to encounter any molecules of interest and therefore may be less attentive, and 2) there is a specific anosmia for it, with 30% of tasters unable to detect it.

But now the days of comparing a glass of Northern Rhône Syrah to a strip of
peppered bacon appear to be coming to an end: Researchers at the École
d’Ingénieurs de PURPAN in Toulouse, France, anticipate that the peppery notes attributed to rotundone in Syrah grown in warmer climates will be lost due to increased temperatures and less precipitation during the ripening stage.

Unlike other aroma compounds in grapes that are derived from odorless precursors released during production or formed during fermentation, rotundone is directly extracted from berry skins during winemaking. In the context of climate change, strategies are being proposed in both the vineyard and the winery to help produce wines with consistent rotundone levels.

In addition to developing drought-tolerant rootstocks, the Toulouse researchers have identified specific clones that produce higher concentrations of rotundone, including Duras clones 554 and 654; they are also focusing on later-ripening clones of varieties like Tardiff, because later picking dates appear to be another significant factor in maximizing rotundone in wines (as do extended macerations in the cellar).

If we lose the peppery notes that we know and love in Syrah and Gamay wines, producers will have the option of recreating those characteristics by blending with wines made from varieties such as Duras and Tardiff.

Loss of complexity is just one indicator of the impact that climate change is having on the characteristics that we associate with benchmark wine styles. And this unfortunate scenario isn’t confined to the warmest growing regions of France. It’s hard to imagine tasting Grüner Veltliner without its characteristic notes of white pepper or losing the fragrant green peppercorn
that is found in Cabernet Franc. Without them, differentiating between
grape varieties will become increasingly more difficult, and consumers will be
forced to look elsewhere for their favorite complex flavors.