Can wine astringency be measured?

Astringency, often described as the dry sensation one feels between the tongue and palate after consuming wine, has intrigued both wine enthusiasts and scientists alike. The phenomenon is a complex interplay of various factors within the oral cavity, and understanding it is crucial for the wine industry. This article delves into the essence of astringency, the role of tannins, and the ongoing search for a way to measure this characteristic scientifically.

The Nature of Astringency

Astringency arises from the encounter between tannins, naturally occurring compounds in wine, and mucin, a protein in our saliva. Saliva proteins lubricate the mouth, ensuring it doesn't feel dry. However, when these proteins interact with tannins, the lubrication is disrupted, manifesting as the sensation of astringency. While red wines are generally associated with this dry feeling, white wines aged in oak barrels can also present a hint of astringency, thanks to tannins from the barrel wood.

Why Measuring Astringency Matters

Being able to measure astringency would benefit those who prefer wines with specific dryness levels. Just as one can identify a wine's alcoholic content or determine if it's sweet or dry, knowing its astringency level would be valuable. Several global studies have embarked on the quest to find a parameter for this measurement, with tribology emerging as a potential solution.

Understanding Tribology in Wine Research

Tribology, a branch of physics that focuses on friction between materials, including liquids, offers insight into this conundrum. In relation to the mouth, tribology considers the myriad interactions within the oral cavity, factoring in saliva, solid food, liquids, and the surfaces of the tongue and palate.

The Tannin Mystery in the Mouth

Researchers propose three hypotheses regarding the interaction between tannins and the mouth:

1. Tannin-protein aggregates attack the surface layer of saliva covering the tongue and palate, causing the dry sensation.
2. Precipitates, or solid phases of substances separating from a liquid solution, form from tannins and proteins. Their presence may cause friction between the tongue and palate, intensifying the sensation.
3. The astringent sensation may stem from the free tannins in wine interacting with the cellular membranes of tissues within the oral cavity.

The Role of Friction in Astringency

To determine a wine's astringency level, one must measure its coefficient of friction (COF) between the tongue and palate. This requires human saliva solutions, challenging to obtain and hence often simulated in labs.

Discoveries and Challenges Ahead

The quest for an astringency indicator began in 2016 using human saliva solutions. Lab-simulated saliva was introduced later, though results have been inconclusive. To date, a purely chemical indicator for measuring astringency remains elusive. However, researchers have identified a direct correlation between a wine's astringency and its COF. This understanding can inform the wine-making process, guiding decisions about the wine's intended astringency level and target audience.