The Cork of Wine Is Not an Accessory, but a Genuine Ingredient: Science Has Proven It
The Cork of Wine Is Not an Accessory, but a Genuine Ingredient: Science Has Proven It
Those accustomed to drinking wine, especially from a bottle, have likely encountered a plastic cork instead of the older and more traditional cork stopper at least once. For decades, the cork has been viewed simply as a sealing system to isolate the bottle's contents from the outside environment.
Of course, more experienced individuals already knew the differences between the two types, but for most people, the cork is merely a component of the bottle. Now, this theory has been definitively disproven by science: the cork is genuinely an ingredient that determines the properties of the wine.
A research study published in Science Advances proposes a much more nuanced understanding of its behavior. According to scientists at the University of Burgundy, cork directly participates in the evolution of wine by regulating the transfer of oxygen and releasing substances that modify the chemical reactions inside the bottle.
Oxygen represents one of the most important factors during the aging of wine. A limited amount encourages maturation, softens tannins, and contributes to the development of greater aromatic complexity. On the other hand, excessive intake accelerates the oxidation of alcohol and phenolic compounds, alters the color of the wine, and compromises its organoleptic characteristics.
However, studying these phenomena directly in a traditional 750 ml bottle presents numerous challenges. The volume of the liquid, the thickness of the glass, and the need to avoid any contamination with external air make it very complicated to measure the transfer of oxygen during aging precisely.
To overcome these limits, researchers designed a miniature experimental system, consisting of small glass vials that replicate the geometry of the necks of regular wine bottles. Each container was sealed with corks ranging from 6 to 42 millimeters in length, filled with a model wine or just gas, and equipped with sensors capable of precisely monitoring changes in oxygen concentration.
The reduction in volume amplified the changes, allowing researchers to observe phenomena that are much more difficult to detect in a traditional bottle. The experiment lasted 18 months and allowed them to identify four distinct phases of oxygen transfer.
The first phase occurs in the fifteen days following bottling. In this phase, the system reaches an equilibrium between the oxygen dissolved in the wine and that present in the small air chamber trapped during the insertion of the cork.
The second phase, extended for about six months, revealed the most interesting surprise. Most of the oxygen that reaches the wine does not come from outside the bottle but directly from the cork itself. Oxygen present in the microscopic cavities of the cork's cellular structure gradually diffuses into the bottle. The analysis also highlighted a difference between the various types of closures. Longer corks release a greater initial amount of oxygen simply because they contain a larger volume of material and thus a greater reserve of gas.
After about four months, an additional mechanism comes into play. The wine begins to extract phenolic compounds from the cork, such as gallic acid, ellagic acid, and protocatechuic acid. These molecules react with the oxygen previously released by the cork, in the presence of small amounts of metals like iron and copper, gradually consuming it. As a result, the cork not only releases oxygen but also helps to reduce its concentration through specific chemical reactions, taking an active role in the system's balance.
The fourth and final phase begins after about 15 months. At this point, oxygen from the external environment slowly passes through the cork and reaches the wine. Researchers observed that in samples sealed with corks longer than 30 millimeters, the transfer rate becomes extremely reduced, so that after 18 months, the variations are almost negligible.
The study does not include tasting tests, so it does not establish which cork produces the best wine from a sensory point of view. The goal is to accurately identify the physical and chemical mechanisms that regulate oxygenation during storage.
The research group believes that this information could have important implications for the wine industry. A deeper understanding of the behavior of different types of cork could allow producers to select the most suitable cork based on the characteristics of the wine and the expected aging period, thus controlling the evolution of the bottle more precisely over time.
Future studies will seek to quantify the contribution of each of the four observed phases and evaluate how different types of cork and various storage conditions can influence oxygen transfer. The ultimate goal is to develop methods that allow for predicting the oxidative potential of a wine right at bottling and choosing the most suitable closure system to achieve the ideal tasting moment.