Issue link: https://read.dmtmag.com/i/63248
WINERY Reducing Reduction Issues By Remi Cohen Technical considerations when bottling with screwcaps The use of screwcap clo- sures has increased dra- matically in the wine industry during the past decade, and recent studies have shown that consumers have become more amenable to pur- chasing wines with screwcaps. According to United Kingdom- based Wine Intel- ligence, acceptance of screwcap closures in the U.K. has risen to 85% of the regular wine- drinking population, com- pared with just 41% when the company first began reporting on this issue eight years ago. And similarly, Wine Intelligence found that the percentage of U.S. wine drinkers who like or accept screwcaps rose to 70%. That said, screwcaps have their issues, too, and as their use becomes more acceptable to the consumer, the wine industry contin- ues to work hard to eliminate some of the potential risks associated with the closures. These issues tend to relate to the ingress, or lack thereof, of oxygen into the bottle through the screwcap and its effect on the oxidation-reduction (redox) potential of wine. Dissolved oxygen in wine can react with phenolics and form acetaldehyde, a prod- uct of oxidation with aromas reminiscent of bruised and browning apples or roast- ed nuts. Detectable quantities of acet- aldehyde are considered to be a flaw in most commercial wines. In winemaking, sulfur dioxide (SO2) is added as a preservative to wine to prevent oxidation and microbial activity. SO2 can react 56 VINEYARD & WINERY MANAGEMENT MAY - JUNE 2012 with the precursors of oxidation and prevent the development of alde- hydes. It can also bind with alde- hydes and render them odorless. As wine ages, free sulfites bind with other compounds and there is a gradual decline in free SO2. When the level of free SO2 falls below 10 ppm, its binding capacity to acetaldehyde is lowered, and alde- hydes may start to appear at levels above sensory thresholds. On the other side of the spec- trum, if a wine is not exposed to sufficient oxygen during fermen- tation and aging, it can become reductive. The term "reductive" has been used as a broad gener- alization for when a wine is above sensory threshold levels of volatile sulfur compounds, such as sulfides and thiols (compounds containing the sulfhydryl –SH functional group and also referred to as mercaptans). These compounds tend to be highly AT A GLANCE Avoiding reduction in wines bot- tled with screwcaps begins in the vineyard. Minimize sulfur use in the vineyard and maintain healthy fermenta- tions to avoid excessive sulfide formation. Consider the intended shelf life of the wine when choosing the type of screwcap. Dissolved oxygen in wine is impor- tant to avoid reduction issues, but too much can lead to premature oxidation. Adjust levels of free SO2 based on your closure choice, shelf life of the wine, and the amount of dis- solved oxygen in the wine. WWW.VWM-ONLINE.COM Photo: Thinkstock