Garnacha wines: the science of aging and aromatic degradation explored

Garnacha wines, native to the Mediterranean region, have historically been perceived as oxidatively unstable, often evolving into amber-hued beverages with sherry-like scents within a few months. Such wines were chiefly appreciated by consumers habituated to this specific category, which would today be termed dessert wines. However, a revolution in vitiviniculture—aided by technological advances and biochemical discoveries—has transformed the once unstable Garnacha wines into vintages that can age with grace, at least in terms of color.

One of the first breakthroughs in stabilizing Garnacha wines was the introduction of technology that limited the wine's exposure to air. This was coupled with the realization that tannins play a crucial role in stabilizing the natural pigments (anthocyanins) responsible for the wine's color. It was discovered that these colorants would condense with tannins in the presence of minimal oxygen levels, thus maintaining the vivid, reddish-blue hues characteristic of young Garnacha wines.

However, while color stability was being mastered, the intricacies of aroma remained a challenging frontier. Many wines, especially those from the Mediterranean regions, develop off-flavors as they age. These often manifest as notes reminiscent of cooked vegetables, raisins, honey, or simply as an aged, "rancio" aroma. Sometimes, the aromatic profile fades away, leading to a loss of freshness and fruitiness that was abundant in the wine's youth.

Over two decades of research led to the identification of two specific odorants, primarily derivatives of amino acids, that were primarily responsible for these aroma-related issues. The first is methional, derived from methionine, with an overpowering scent of raw potato. The second is phenylacetaldehyde, originating from phenylalanine, which smells like honey. Even at microgram per liter concentrations, these compounds significantly impact the aroma of wines and are formed through various biochemical pathways, complicating the understanding of their behavior.

Two key pathways were identified through which these odorants can form independently of direct oxygen involvement. The first pathway is during alcoholic fermentation, where these molecules act as biochemical intermediaries in amino acid synthesis. In the presence of sulfur dioxide (SO₂), a common antioxidant and antiseptic in winemaking, these odorants form an association that renders them odorless, at least temporarily. As wine ages and SO₂ dissipates, these odorants re-emerge, spoiling the wine's aroma. The second pathway involves a chemical reaction known as Strecker degradation, wherein these amino acids react with alpha-dicarbonyl molecules.

The key to extending the lifespan of wines lies in controlling these pathways. Ongoing research aims at optimizing fermentation conditions and yeast types to minimize the formation of these aldehydes and dicarbonyls. Furthermore, the optimal blend of grape varieties is being studied to inhibit undesirable reactions during oxidation. Preliminary laboratory trials confirm the possibility of completely avoiding the formation of aroma-degrading aldehydes, making wines more enduring if not eternal.

The advances in the understanding of Garnacha wines have come a long way in solving the issues of color and are making strides in the complex arena of aroma stability. With continued research and technological innovation, the future holds the promise of Garnacha wines that not only age gracefully in color but also in aroma.