Chapter 12

Wine Packaging

Wine Bottle Closures

Until the early 1980s, natural cork was basically the only material used by the wine industry to close a bottle of wine. Cork was the only choice because it was considered the perfect material, unchallenged by centuries of winemaking practice. Today, producers and consumers can choose from many types of wine closures. In recent years, three types of wine closures have clearly dominated the market: natural corks, synthetic corks, and screw caps.

Natural Corks

Cork is a natural product from the bark of a type of evergreen oak tree, Quercus suber (Figure 12.3). Portugal produces over half the world' s cork. Cork has characteristics that make it very useful as a bottle closure. It is cheap, readily available, comes from a renewable source, is biodegradable, and is a good oxygen barrier. It is elastic, can be compressed, and will quickly regain its original size. It possesses an amazing anti-slip property which holds it in place without undue force from the cork itself.

Colmated

Colmated cork is natural cork that has been coated with waxes, silicones, paraffin, or other polymers in order to make insertion and extraction easier.

Technical Specifications

Corks are available in different sizes. Bottles are molded to a number of varying diameters, for which matching cork diameters are needed. A cork with a smaller or larger than recommended diameter should not be used. The smaller diameter cork will not exert enough pressure to prove an effective seal and may result in leaking or increased oxygen ingress.

Technical Corks

Technical corks are the result of natural cork production by-products converted into granules, which are conglomerated using an approved binder (e.g., polyurethane glue). This class includes agglomerated corks with larger granules (2-9mm), micro-agglomerated corks with smaller granules (0.5-2mm), and corks composed of a densely agglomerated cork body, with two discs of natural cork glued in one.

Synthetic Corks

Synthetic corks are produced through two different methods, namely polymer injection and co-extrusion. The materials used comply with the FDA food regulations. Synthetic corks have several technical attributes that make them an attractive alternative to natural cork. The corks do not contain as many volatile compounds as natural corks, and they are not susceptible to the growth of microorganisms.

Screw Caps

Screw caps are made up of two components - the aluminum-based outer cap and sleeve and the liner (Figure12.4). The liner (also known as the gasket or wad) is the most critical part of the screw cap in winemaking because it is this which is effectively the closure.

Liners

Two different liners are manufactured for screw caps used in the wine industry. The Saran-tin liner, composed of successive layers of polyethylene (PE), Kraft paper, tin or aluminum, and polyvinylidene chloride (PVDC), is almost impermeable, exhibiting the lowest oxygen transmission rate (OTR) values.

Oxygen Transmission Rate

Oxygen transmission rate (OTR) is a measure of the volume of oxygen that diffuses through a barrier over a given period of time. This is probably the single most important factor to consider during closure selection. Depending on the materials and technology adopted to produce the closure, OTR can vary to a large extent.

Post-Bottling Reductive Off-Flavors

Differences in the frequency and intensity of reductive offflavors post-bottling are attributed in particular to different OTR-values of bottle closures. Oxygen ingress through natural or synthetic corks helps in reducing the affect of reductive off-flavors.

Optimal OTR

Under commercial winemaking conditions, it is impossible to predict for each wine an optimal closure OTR, above which it would not produce a noticeable reductive flavor post-bottling. That OTR must be at least high enough to prevent the accumulation of sulfur compounds, based on sensory experience, but not too high as to trigger excessive oxidation.

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