One of the most important processes in the production of cork stoppers is polishing and finishing. The objective is to give the final shape to the cork for the different types of wine, as well as to ensure its consistency and size. A poor finish means irregular insertion of the stopper into the bottle and possible difficulties when being extracted.
This is why it is important for cork stoppers to be finished perfectly to ensure that the consumer experience is as expected, and that the wine does not suffer external factors that could compromise its drinkability.
Common problems with cork stopper finishes
Although the quality of sparkling wine and the experience of drinking it depend to a large extent on a good cork stopper that ensures it is sealed correctly, the reality is that imperfect finishes sometimes occur that fail to meet this objective.
In this respect, there are different types of common problems that can occur in cork stopper finishes:
- Aesthetic problems, which in principle only affect the cork design itself, with no consequences for the quality of the wine. Usually problems caused by a poorly rolled stopper.
- Technical problems, caused by a poor stopper finish include possible gas leakage due to a scratched surface on the cylindrical part of the stopper; inadequate responsiveness in the bottling and uncorking process due to the cork being too rough; and finally, a misalignment on the line due to poor chamfer formation.
Polishing and finishing process
Several processes are involved in the polishing and finishing of cork stoppers in order to obtain an adequate result to ensure the quality and experience of sparkling wines.
Washing, sterilizing and drying
It is essential to wash the cork before the cork stopper is made.
Special environmentally-friendly processes are used to wash and sterilize the cork. This removes any microorganisms that could contaminate the product. It is then dried to rapidly reduce humidity and remove the risk of fungal growth. Cork humidity is monitored and kept within the appropriate parameters for preservation (between 4 and 8%). This process can be carried out with the use of heaters or well-ventilated stores.
Shaping and polishing
After the cork is ground into granules, it is unified again to form the body of the stopper through a compression process and bound with a special food grade glue.
This process is essential to give the stopper body a uniform composition and density to create the main body of the stopper to which the natural cork discs will be adhered.
In order for the stoppers to have the correct dimensions and a fully cylindrical shape, one or more polishing operations are required after final assembly. Poor control of the polishing process can lead to scratched or rough stoppers.
For a good surface finish it is necessary to polish the stopper in several stages, starting with smoothing down the surface of the stopper, through to the last stage of buffing the surface of the stopper with a very fine emery belt.
Chamfering
Sparkling wine cork stoppers have a chamfered top, which is made by special machines.
For proper chamfering, these machines are equipped with an abrasive belt angled at 45 degrees to the stopper’s axis of rotation. The stoppers are rolled through a guide and, as they reach the height of the abrasive belt, they are chamfered on one end.
The chamfer can be of various sizes, but the most common is around 4 mm.
Surface treatment
The final surface treatment is crucial to guaranteeing a smooth and fluid bottling process with regular compression and insertion forces vital for the proper functioning of the bottling line.
If the stopper exerts excessive resistance against the bottleneck during the bottling process, it may cause the stopper or the bottle itself to break.
To eliminate this friction, all sparkling wine stoppers are treated with a light layer of food grade silicone elastomer that allows the stopper to be gently inserted into the bottleneck.
This treatment can be adjusted according to the specific needs of each winery to achieve the exact finish desired. Remember that correct siliconization means the bottle can be uncorked properly, which is very important for a good consumer experience.
Key points to remember
Although work is being done to implement quality standards, the fact is that, at present, each manufacturer uses its own internal production processes, which do not always guarantee a perfect finish. This is why it is important to rely on a quality supplier with industry experience and sparkling wine stopper expertise.
At TESA, we implement the strictest quality controls when manufacturing and producing sparkling wine cork stoppers. The secret to our stoppers lies in our meticulous selection of raw materials and the quality controls to which they are subjected to at all stages in the process.
If you would like more information, please get in touch with us. We would be delighted to help you.