Destemming or separating the fruit from the grape stalk—also known as the rachis, to which each berry is connected through smaller stalks called pedicels— prior to fermentation is standard practice in modern winemaking, but the discovery of new compounds in wine grape stems has prompted researchers in Bordeaux to re-evaluate the benefits of including stems during this crucial stage of production.

Whole-cluster winemaking has long been associated with the nouveau wine style of Beaujolais, which relies on carbonic maceration for its juicy, primary flavors; stems are also traditionally employed in Burgundy, Côtes du Rhône, Corsica, and Barolo, but as destemming technology evolved, the practice fell out of favor in regions like Bordeaux.

The decision to include stems in a fermentation is often made with the intention of bolstering the tannin expression in wine, as phenolic compounds abound in stems. But as researchers at the Laboratoire Excell biochemistry lab in Floirac, France, have learned, there is far more to wine grape stem compounds than previously thought: It’s been discovered that they contain the salicylate family of molecules and Astilbin, which is shedding more light on how the inclusion of stems during fermentation impacts wine beyond the contribution of tannins.

Astilbin is a well-known compound in Chinese herbal medicine typically extracted from the flower Astilbe thunbergii (false goat’s beard). Studies have shown that it has anti-inflammatory and antioxidant benefits and shows potential in the treatment of kidney disease and obesity.

Stem compounds reduce alcohol

According to one of the researchers, Frédéric Massie, a technical consultant for wine-consulting firm Derenoncourt Consultants near Vienne, France, the addition of stems can decrease actual alcohol levels in wine: The stems can not only dilute the wine by releasing water but also absorb alcohol. Astilbin, meanwhile, reduces the perception of alcohol, as its presence contributes to the impression of sweetness, density, and texture.

“The perception of alcohol is the balance between the level of alcohol and the density of the wine. [When compared to another wine with] the same level of alcohol, a wine with more density will appear [more] balanced,” he says. Of the Merlot, Cabernet Sauvignon, and Cabernet Franc wines evaluated by the researchers, Merlot showed the highest concentrations of Astilbin by a significant margin.

The salicylate family of compounds, meanwhile, are of particular interest to perfumer and winemaker Cédric Alfenore of Biolandes, a flavor and aroma manufacturer in Le Sen, France, who also participated in the research study. He explains that ethyl and methyl salicylates contribute nuances of freshness to wine with aromas that include juniper needles; wintergreen-dominant medicinal aromas like camphor; vegetal notes of green pepper and tomato leaf; and cut grass, herbs, and white flowers.

These characteristics will be more or less perceptible depending on the concentration of salicylates: Higher levels mean more freshness.
In addition to the salicylates, Alfenore notes that there are floral terpenes (citronellol, geraniol, oxy rose); benzaldehyde (a compound that contributes notes of almond and cherry); and fatty acids such as myristic found in stems. While they are present in very small amounts and their concentrations vary depending on soil type, grape variety, and vintage, their presence results in a bouquet of aromas and incredible flavors.