Types of Corks
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Cork stoppers are the most famous product of the cork industry. It is the most produced and most exported. More than 12 billion bottles of wine are closed every year with cork, keeping all the qualities of this drink intact for centuries. The cork stopper has been the closure par excellence of wine for many years, chosen by more than 70% of producers. Cork’s relationship with wine began in ancient Egypt as a closure for amphorae.
Unique Properties of Corks
The natural properties of the cork stopper afford the wine industry a stopper with incomparable characteristics. Lightness (a cork contains about 90% of air or similar gas), flexibility, elasticity and compressibility (given by the 750,000,000 cells) allow the cork stopper to regains its initial form, ensuring a perfect adaptation to the neck of the bottle. This adaptation is dynamic over time, as it accompanies the expansions and contractions that the glass undergoes due to variations in the temperature of the environment, ensuring that the bottle remains sealed. Impermeability to liquids, virtually impervious to gases and the imputrescible nature that ensures high resistance to moisture and thus to oxidation, are important features which make cork stoppers the preferred closure of producers and consumers.
The most common formats in the market are:
Natural Cork Closures
Cork stoppers ensure the sealing of wine in a glass recipient. If this sealing is prolonged over time it promotes the wine’s maturing, which is to say there is an evolution by means of numerous physical and chemical processes between the components or between these and the substances inside the bottle. This gradual evolution of the bottled wine occurs in an environment with a very low oxygen content, but which is necessary and sufficient for the correct ageing of the wine. Until now, only the natural cork stopper has been able to provide this perfect balance, allowing for the correct evolution of the wine and the formation of the much appreciated “bouquet.” The bouquet consists of a set of pleasant aromas, which develop during the maturation period of bottled wine. It is a valued element, which depends on the intrinsic quality of the wine and the conditions in which it matures.
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The hermetic quality ensured by the cork stopper is not only indispensable to maturing wines, but is also necessary for wines which will be consumed more quickly. Natural stoppers enable the excellent conservation of wines while preventing interference in the harmony of their components, conferring a sign of quality to the wine. Due to cork’s cell construction, compressibility and elasticity, it is the only closure capable of assuring this type of conservation in any type of wine.
Only natural material is able to adapt correctly to the internal irregularities of the neck, guaranteeing perfect sealing, even if the glass expands or contracts, which can happen when the ambient temperature changes during shipping or storage.
A perfect seal can be expected for decades. This sealing can be prolonged for even longer when high-quality cork stoppers are used, bottling rules are complied with and it is stored in ideal storage conditions (suitable temperature, pressure and humidity and without great variations in temperature during the day or seasons of the year).
The use of longer stoppers is common in wines associated with longer bottled maturing. However, it should be noted that the quality of the seal over time depends more on the appropriate choice of the diameter of the stopper than on its length. Ideally, a stopper should be used that is at least 6 mm wider than the smallest diameter of the neck of the bottle, taking care that it should not be compressed by more than 33% of its diameter when inserted into the bottle, as this may damage its cellular structure.
The most common formats in the market are:
Colmated Corks
Colmated stoppers are natural cork stoppers with pores (lenticels)that are filled with the cork powder resulting from the finishing of natural stoppers. A glue based on natural resin and natural rubber is used to fix the dust in the pores. A water-based glue is also currently used in this process.
This process is primarily used to improve the visual aspect of the stopper and its performance.
These stoppers are of quite homogenous appearance and have good mechanical characteristics. They are fabricated in the widest range of shapes and sizes. However the most common cylindrical form and sizes are those indicated below (length x diameter), although these may vary from one manufacturer to the next.
Champagne and Sparkling Wine Stoppers
These are stoppers, as the name suggests, especially designed to close champagne, sparkling wines and cider. The Champagne stoppers are considered to be part of the family of technical stoppers, as these are produced from a body formed by agglomerated granules of cork, to which one, two or three discs of selected natural cork are attached to one of the ends.
Champagne cork stoppers have a larger diameter than average corks. Their larger diameter is essential for retaining the high internal pressures in wine bottles containing gas. To obtain the best chemical and physical performance, Champagne stoppers are subject to careful fabrication and a tight quality control.
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Champagne stoppers come in alternative formats: 0+2 or 0+1, or just simple agglomerated or microgranules, without discs. Champagne corks on which discs are used basically fall into the following classes: Extra, Superior, 1st and 2nd, and are associated with the quality of the disc.
The most common formats in the market are:
Technical 1+1 Corks
Technical stoppers were designed for bottling of wines to be consumed, in general, within two or three years. These consist of a very dense agglomerated cork body with discs of natural cork glued to its top or both ends. Technical stoppers with a disc at each end are called 1+1 technical stoppers and those with two discs at just one end are called 2+0 technical stoppers.
Agglutinins approved for use in products that will come into contact with foods are used to glue the discs of cork to the ends of the cylinder of agglomerated cork.
This type of closure is chemically very stable and mechanically very resistant. They behave very well under the torsion to which they are submitted when bottling and uncorking. They have proven to be excellent stoppers over time (Australian Wine Research Institute, Wine Bottle Closure Trial), managing to maintain the necessary concentration of free SO2 in the bottle, preventing premature oxidation of the wine while not developing unpleasant reduction aromas.
As the body of these stoppers is agglomerated, the quality of the technical stopper is quite homogenous. However, the visual standard of the natural cork discs used at their ends varies. This standard is generally classified in 3 classes. This standard presumes an agreement is made by the producer and the user on the basis of a sample to be used as a benchmark.
The most common formats in the market are:
Agglomerated Stoppers
Cork stoppers manufactured entirely from cork granules derived from by-products resulting from the production of natural stoppers. Agglomerated stoppers may be fabricated by individual molding or by extrusion. The agglutinating substance used to bind the cork granulates in both of these methods is approved for use in materials that come into contact with foods.
Agglomerated stoppers are a cost-effective solution that ensure perfect sealing for a period that should not, in general, exceed 24 months. In addition to the economic advantage of lower priced wines and high turnover on the market, these stoppers also have the advantage of being completely homogenous within a batch. This product is the result of a highly industrialized process, and the categories are defined on the basis of the size of cork granule and final density of the product, whose characteristics are later adjusted with the surface treatment used.
Natural Cork Council requirements define cork stoppers to include a minimum of 75% natural cork material. This requirements allows the stopper to display physical behavior consistent with natural cork stoppers. Some unapproved agglomerated stoppers contain lower amounts of cork and must introduce plastic micro-spheres to provide resiliency.
Most common measurements:
27×20 mm 27×19,5 mm 27×18,5 mm 24×17 mm (20 cl bottles) 18×13,5 mm (miniature bottles)
Bar Top Corks
A capped stopper is a cork stopper where the end is placed in a cap of wood, PVC, porcelain, metal, glass or other materials. The capped stopper is generally used with liqueur/fortified wines or spirits which are ready to drink when made available for sale in the market. The major examples are port, Madeira sherry, Calvados, muscatel from Setubal, and also whisky, vodka, cognac, armagnac, brandy, liqueurs, and clear spirits.
This stopper is very practical for bartenders and consumers, as it allows for easy reuse, an important factor for bottles whose content is not consumed in one sitting.
The most common formats on the market have the dimensions for the most commonly used sizes of bottles. Note that with this type of stopper, it is not necessary that for it to have a diameter of 6 mm more than the internal diameter of the bottle neck. In fact, 2 mm is sufficient without compromising good sealing to allow for easy reuse in the bottle.