Reviews

Oxygen, closures and wine
«Vinnaya Karta» №8 (89) October 2007, "Vitrina" November 2007

Producer of artificial corks Nomacorc is known through its innovative research programmes which study various types of closures and their interaction with wine.

The company ran a series of seminars dedicated to influence of oxygen on wine and impact of various closures on the process.

Nomacorc is a leader on the market of synthetic wines corks. Founded in 1999, the company is the largest world producer in its class today. One of the key Nomacorc’s know-hows is a production technology that helps control air penetration in bottles with wine. The company spends money on research of chemical reactions in wine after bottling as it believes that oxygen penetration through closures is an essential element that influences wine’s quality and evolution. This year Nomacorc presented some findings of the research.

According to the statistics of The International Wine Challenge, 7,2% of all samples have various defects of which about a half is connected to closures. Thus closure problems can be found in one out of 28 bottles.

Wine corks and other closures serve several purposes. They must preserve quality of wine, prevent leaks and control air penetration. In the case of the former oxygen is usually meant as the most active element that causes changes in the chemical structure of wine.

When studying oxygen impact on wine, researchers use the term OTR, or oxygen transfer rate). This is the amount of oxygen that penetrates through a closure in a certain period of time.

Oxygen management involves all production stages from vinification to sale. Such factors as open or closed tanks, temperature, use of microoxygenation techniques, types and volume of aging vessels are important during fermentation and aging. Bottling is another critical moment where presence or absence of vacuum systems, choice of bottle and closure types play key role.

When the wine is in the bottle, its quality preservation depends on external and internal factors. Among the former are temperature, humidity, vibration, sunlight, etc. The volume of wine in the bottle is the internal factor.

It is widely accepted that the longer the cork, the less oxygen goes through and wine keeps better. Nomacorc research showed that it is not always the case. Much depends on a bottle neck. If a cork is long, but doesn’t fit tightly to the walls, real effectiveness is lower than expected. There are two solutions here — either to take bigger diameter corks to ensure a full contact between the closure and the bottle neck, or to buy shorter corks to fit bottles of all types (but then there is a problem of high OTR).

Which other winemaker’s actions can help preserve wine’s quality to minimize negative impact of oxygen? The bottling stage is critically important as this is when oxygen gets into the bottle. Sulphur is used to stabilize wine. It is now known that 4 mg of SO2 are needed to neutralize 1 mg of O2. It is not difficult to calculate ratio of sulphur to use with this ratio. A winemaker can also choose corks with various OTR depending on the wine’s projected shelf life.

OTR impact can be analysed from the technical and organoleptic points of view. Scientists present information in chemical formulas (mercaptans, pyrazines, volatile acids, etc.) while tasters talk about aromas and flavours (rotten egg, cabbage, vinegar, nuts, honey, caramel…)

Winemakers most often ask the following questions when choosing wine closures. How to preserve fruit without reduction (especially for Australian white wines where this issue occurs with screw caps)? What will the wine’s structure be like if oxygen doesn’t get in the wine?

New Zealand Sauvignon Blanc that is normally vinified in anaerobic conditions needs closures with medium OTR figure. It prevents reductive aromas and preserves Sauvignon’s characteristic bright aromas. For Merlot with a two-year shelf life a closure with a low OTR will suit best. The similar Merlot, but with the aging potential of 5 years, needs a closure with a very low OTR.

In general, the choice of closures with various OTR levels depends on the grape variety, vinification methods, contact with oxygen and its amount, a general wine’s style and aging potential. Oxygen transfer rate is one of the key aspects for wine’s preservation that demands closer attention from the industry and further research.