xygen ingress after bottling causes quality loss in wine. Long-term trials are often carried out to assess the oxygen barrier properties of different wine bottle closures. At the commencement of these trials, bottles are filled with the same wine under the same conditions and sealed using different closures. Analyses are then performed at fixed time intervals after bottling (for example 1, 3, 6, 9, 12 months) to evaluate changes in the wine that are induced by reactions with oxygen, such as loss of sulfur dioxide, loss of ascorbic acid, and generation of brown color.

In these trials, however, it is often difficult to differentiate between the impacts of oxygen that has been included in the bottle at filling (dissolved oxygen in the wine, oxygen included in the bottle headspace gas, and oxygen contained in the closure) and oxygen that enters the bottle through the closure after the bottle has been sealed.

Negative control bottles can be used to assess the relative impact of oxygen included in the bottle at filling and oxygen that enters the bottle through the closure after sealing . These bottles are filled and sealed under identical conditions to the test bottles, but are treated after sealing to prevent oxygen entry through the closure. Testing of negative controls should be carried out at each time-interval throughout the trial. The wine in these bottles will only be affected by oxygen included in the bottle at filling.

In the past, a number of techniques have been used to prevent oxygen entry through inserted closures (corks or synthetic closures) during long-term trials. The Australian Wine Research Institute covered the tops of inserted closures with epoxy glue soon after bottling (AWRI Annual Report 2001). The Chambre d’Agriculture de Gironde covered the tops of closures with wax in a closure study reported in 2004 (C. Chassagnou, pers.comm.). E. Waters and P.Williams (1997) used bottles with a screw cap neck finish. After insertion of the closure, high-barrier screw caps were applied to bottles selected as negative controls.

An easily applied seal that provides an effective barrier to oxygen transfer through inserted closures has recently been developed. The technique uses epoxy glue and standard 50 mm diameter laboratory watch glasses. The following steps are used:

Wine is filled into bottles using normal commercial techniques.

Closures are inserted so that the top of the closure is 1–2 mm below the bottle rim.

The tops of the neck rims of bottles selected as negative controls are lightly abraded with sandpaper to ensure that they are clean and slightly roughened.

Two-pack epoxy gluewith a thick consistency (such as Araldite™ or Epiglue™) is mixed and placed on top of each closure, and on the rim of each bottle.

A 50 mm watch glass is then placed over the neck of each bottle. The watch glass is placed so that its convex (domed) surface is toward the bottle rim.

The watch glass is pressed down onto the bottle rim. Glue movement is observed through the watch glass to ensure that there is a complete glue seal between the bottle neck and the watch glass.

The bottles are left upright until the epoxy glue has cured.

When analysis of wine in the negative control bottles will be performed, heat is applied to the upper surface of the watch glass using a gas flame or hot air gun until the epoxy glue softens. The watch glass can then be removed from the bottle.

A corkscrew can then be used to remove the closure in the conventional manner.

This technique can also be used to provide negative controls during oxygen transfer rate testing of inserted closures using luminescence systems such as PreSens and Oxysense. The use of secure negative controls ensures that clear differentiation can be made between oxygen already in the bottle at filling, and oxygen that enters the bottle through the closure after sealing has been completed.

2. Waters, E. and P. Williams (1997). The role of corks in the random oxidation of bottled wines. Australian Wine Industry Journal 2: 189–193

Closure inserted into the bottle neck

Gas flame applied to the watch glass

Watch glass applied to the bottle rim

Closure and bottle rim covered with epoxy glue