Wine Arcana

Concept

Wine closures

Also known as Bottle closures, Screwcap, Screw cap

A wine closure seals the bottle and helps determine how the wine develops after packaging. Natural and technical corks, synthetic and glass stoppers, and screwcaps differ in construction and oxygen transfer. Their performance also depends on the bottle, correct application, and the wine's condition at bottling.

Oxygen already present and oxygen entering later

Wine carries some dissolved oxygen into the bottle; more may remain in the headspace or closure. This initial total package oxygen can consume protective sulfur dioxide. Subsequent oxygen entering through the closure adds a separate influence during storage.

The oxygen transmission rate, or OTR, describes that later entry. Closure types have different ranges, and individual closures of one type can also vary. Peter Godden's summary of Australian Wine Research Institute (AWRI) trials identifies both the transfer rate and consistency between bottles as important performance measures.1. Peter Godden, “Summary of AWRI closure trials and other investigations into closure performance,” pp. 6–12.

How screwcaps seal

A screwcap's metal casing holds a liner against the bottle rim. The liner and the quality of that contact form the seal. The external appearance therefore does not reveal all of its oxygen-transfer properties.

AWRI distinguishes commonly used Saran Tin and Saranex liners. The tin layer provides a stronger oxygen barrier, while other constructions allow greater transfer. Producers can choose a closure to suit a wine's composition and intended development. Application checks also matter: an incorrectly fitted cap cannot be assessed as though it formed the intended seal.

Taint, oxidation, and sulfur aromas

Cork taint is commonly associated with 2,4,6-trichloroanisole, or TCA. It can give a musty smell and suppress fruit aroma. The compound can also arise from sources such as contaminated oak, so a wine can show TCA character without a cork-derived contamination.

Oxidation is a different process. Oxygen exposure and the wine's reactive constituents determine the resulting loss of fruit, colour changes, and development. Some sulfur aromas associated with reduction are more likely to become apparent under very low oxygen entry when the wine already has a propensity to develop them. Closure and cellar preparation therefore work together.

Bottle development

Low oxygen transfer can preserve fruit and still allow bottle ageing. Reactions among compounds already in the wine continue after sealing. AWRI's trials and later comparative tastings show how different closures alter preservation and bottle consistency, with results tied to the wines and closures tested.

For the drinker, the closure supplies information about packaging and the producer's choices. Assessing ageability also requires the wine's composition, storage history, and the desired stage of maturity.

Sources