Cork Stoppers. Storing. Bottling. Shipping

Whenever possible, cork stoppers must be used soon after being received. Long periods of storage should be avoided. The maximum advisable period is up to 6 months, in the appropriate storage conditions. 

Stopper packaging should only be opened when stoppers are to be used. Stoppers are generally packaged in bags containing SO2. This gas acts both as an anti-septic and antioxidant, protecting the stoppers.

Unused stoppers should be returned to packaging in bags with SO2 (between 0.5 g and 4 g of SO2 per bag of 1000 stoppers).

Storage of the stoppers should be:

• In ventilated and dry places with a mild and stable temperature between 15ºC (59F) and 20ºC (68F) and a relative humidity level between 50% and 70%;
• In places free of smells and without mould, away from any type of fuel, or products containing chemicals, such as cleaning products or paints, for example;
• In places where there is no wood treated with chloride products (for example in structures with recently built roofs, or on shipping pallets);
• Compliance with all these recommendations is essential so that when bottling, the stoppers continue to have the same physical and chemical characteristics and are not subject to any kind of outside contamination.

The place where the wine is bottled is essential to the whole process. It should be:

• free of insects, especially wine moths;
• correctly ventilated using a powered ventilation/extraction system;
• at a constant ambient temperature of between 15 and 20ºC (59F to 68F).

Other precautions to take into account when bottling:

• The bottles should be removed from the palettes only at the time of bottling. Before bottling, the bottles must be well washed and thoroughly dried (almost all bottling machines do this automatically).
• Pallets with bottles should be kept in a warehouse at moderate temperatures and in a dry place, free of mould and free of chloride compound treated woods. The pallets should have planks which are not made of cardboard or wooden composite material to separate the bottles from other materials.
• Never wash the stoppers in water or wine before bottling. In the past this technique was used to clean the stoppers or to facilitate their insertion into the neck, but this meant that these liquids accumulated in the pores of the stopper, and developed tastes and aromas that could transfer to the wine. Stoppers are currently provided fully ready to be used, and need no treatment or any additional procedure. If it is necessary to clean the corks for any other reason, then a sulphite solution releasing SO2 is advisable.
• The interior of the neck of the bottle must be clean and dry. A damp neck has a thin incompressible liquid film which hinders the expansion of the stopper, as well as reducing its adherence to the glass.
• In standard bottles, the top of the stopper should not be more than 1 mm below the top of the neck. The stopper should ideally be +/- 0.5mm from the top of the neck. If the stopper is too far in, this may cause a rise in the internal pressure (when bottling by vacuum or CO2 is not used) and create a space between the stopper and the capsule which will only serve to promote the formation of fungus. If the stopper is too far out, there will certainly be problems when it comes to placing the capsule.
• Stoppers with humidity of less than 4% should undergo a process of rehydration at the supplier’s premises and stoppers with humidity of more than 9% should undergo a process of drying at the supplier’s premises and confirmation of sensory quality which may be compromised because of possible fungal development.

Making use of the compressibility of cork, the machine compresses the stopper so that it can be inserted into the neck of the bottle. Suitable compression is when the stopper is 2mm smaller than the diameter of the neck at the entrance, and compression greater than 33% of the diameter of the stopper is to be avoided. Thus, a stopper of 24mm in diameter should be compressed to 16.5 mm for insertion into a neck of 18.5mm in diameter.

Compression must never be more than 33% of the diameter of the stopper, as there is a risk that this could compromise its elasticity, with loss of part of the memory and consequent difficulty in the correct sealing of the wine in the bottle. Thus, for a stopper of 24mm in diameter, the recommended compression is about 8mm (which is equivalent to the 16.5mm as mentioned previously).

Making use of its elasticity, the stopper recovers its volume in the first 5 to 10 minutes after being corked, adapting itself to all the irregularities of the neck; and, after just one hour, a uniform force is exercised over the whole surface of the glass. It is therefore not advisable that the bottle be placed in the horizontal position soon after being corked.

In the case of bottling lines where corking comes immediately before the bottles are laid horizontally in the their boxes, the risks can be minimized by prolonging the time that the bottle remains on the production track from the corking machine to the labelling machine. All that is needed is to add more sections of track, making a tight “S” bend so that space is not wasted.

Bottled wine, except in rare cases, is not immune to environmental temperature variations during its transportation and even when it is in the distributors’ warehouse. These temperature variations are responsible for:

• changes in the diameter of the neck of the bottle due to the natural effects of contraction or expansion of the glass;
• changes in the volume of the wine. As a guide, wine expands on average about 0.2ml for each degree centigrade (33.8F) of rise in temperature, increasing the internal pressure in direct proportion.

Although the variations in diameter of the neck can naturally be compensated by the excellent elastic properties of the cork, the same cannot be said in relation to the variation in volume of the wine and consequent change in internal pressure.

To avoid this problem, the following recommendations should be followed at the time of bottling:

• Bottle the wine at an ambient temperature between 15°C and 20°C (59F to 68F) to obtain an appropriate volume of the wine;
• The bottling machine, with the correct selection of the length of the stopper, should be calibrated to allow at least a space of 15mm between the surface of the wine and the stopper (values for 750 ml bottles). This free space is essential to allow the expansion of the wine if the temperature rises during shipping or storage;
• This space should be greater for sparkling wines;
• To minimize the effects of alteration of the internal pressure which may lead to leakage of the wine, it is recommended that it be done in a vacuum or by injecting CO2. The CO2 is gradually absorbed by the wine and ends up creating a small amount of depressurization inside the bottle. Bottling under vacuum or with CO2 injection will better protect the wine against premature oxidation and may help to prevent microbial multiplication;
• The internal pressure of bottles that have just left the bottling line must be checked frequently to confirm that the vacuum or injection of CO2 system is functioning correctly. The internal pressures should be as close as possible to zero for still wines;
• In extreme conditions, high internal pressures hinder the perfect adaptation of the stopper to the neck after bottling and tend to force the discharge of wine in order for the internal pressure to obtain equilibrium. In these cases, the wine does not leak continually, but a few millilitres are expelled until the internal pressure is re-established. This is not a problem with the stopper, but rather with the internal pressure of the bottle.

Because of the adverse conditions that bottled wine is subject to during the long journeys to be made to arrive at its destination, it is recommended that bottles always be transported in the vertical position.

The use of thermally insulated containers is recommended and the cooler seasons of the year should always be chosen to ship wines, especially for wines which have to be shipped between continents.

If the wine is to be shipped in maritime containers, the last type of cargo used in the container should be informed. If the container is not clean, free of smells and completely dry, it must be rejected. If this is not possible, it should be cleaned with a solution of metabisulfite and then properly dried, for example. Humidity due to condensation during shipping leads to the appearance of fungi which may later lead to the formation of chloroanisoles or other compounds responsible for undesirable odours.

The expression “the cellar makes the wine” is as old as it is true. The temperature, humidity and hygiene of a cellar contribute to the final quality of the wine. The cellar should have the following characteristics:

• Room temperature between 15º C (59F) and 20º C (68F), without great thermal amplitude, during the day and throughout the year:
• Humidity between 50% and 70%;
• The cellar must be free of insects and rodents. This does not include spiders as they are excellent insect predators;
• The cellars must not have chemically treated wood;
• The cellars must be odour free;
• Chemical products, such as paints or cleaning products, must not be stored in the cellar;
• The bottles must be kept in a horizontal position so that the wine is in contact with the stopper and it keeps its excellent elastic properties.

Technical Cork Stoppers Manual click here.