|Cellars have been debating the problems surrounding cork closures for many years. As a result, various alternative products have been devised.
Despite these alternative products, cork closures in different guises are still being used in all wine countries and cork suppliers have also launched innovative actions to improve their products. As a product, screwcaps have been subject to ongoing evaluation.
The first international screwcap symposium was held in New Zealand towards the end of 2004. At this symposium it was mentioned that certain countries, especially France, Italy and the USA, were reluctant to use screwcaps for their wines. New Zealand and Australia on the other hand were among the first countries who saw merit in the use thereof. Since screwcaps ensure the retention of more carbon dioxide in young wines, cellars should take care not to bottle wines with excessively high levels of carbon dioxide in this way (Hawkes, 2005).
One of the most important reasons for concern about bottle closures is the variations that occur among the same type of closure. Although this is a common phenomenon among cork closures, it occurs with other closures as well. This is especially true with regard to the oxygen permeability of bottle closures. Excessive exposure to oxygen via the bottle closure may result in accelerated maturation, whereas limited exposure to oxygen may result in a reductive character in the wines (Phillips, 2005).
The bottling of wines with screwcaps prevents cork spoilage, ensures constant and prolonged maturation, requires lower sulphur dioxide qualities at the time of bottling and it is also easier to open such bottles. Screwcaps have been used for many years. Aluminium closures, better known as ROTE (Roll-on-tamper-evident) and ROPP (Roll-on-pilfer-proof), were introduced as early as 1960. Already in 1933 researchers developed the most important liners for screwcaps. Well-known cellars such as Gallo have been using screwcaps for more than 30 years. However, the success of screwcaps is determined mainly by the suppliers, the integrity of the glass bottles and the application of the closure to the bottle.
There are various suppliers of screwcaps throughout the world and by complying with quality management systems such as ISO 9000 and HACCP and regulatory prescriptions, the suppliers’ integrity is largely ensured. The use of the correct closure lining is extremely important mainly to restrict the oxygen permeability. Compared to natural and synthetic corks, screwcaps have the lowest oxygen permeability by far.
All screwcaps are not compatible with all glass bottles and vice versa. It is of critical importance for the neck diameter of the bottle to be compatible with the closure and capping machine. One of the problems in this regard is that bottle and closure suppliers do not communicate well with each other. Before and during bottling different inspections must take place to ensure successful bottle closure. Screwcaps are usually supplied in carton containers and care must be taken that neither the containers nor the plastic bags in which they are packed, are damaged. Damaged cartons may result in the distortion of closures and open bags may cause dust and other undesirable matter to end up in the wine. Care should be taken that the bottles to be used have the correct neck specifications.
Alignment of the equipment that twists the screwcap onto the bottle, is critical. The application of the screwcap is a complex process and users must ensure that it is employed correctly. The fill height for bottles with screwcaps is extremely important to normalise the pressure in the bottle on the one hand, and to limit oxygen exposure on the other hand. In general 2% of the wine volume in the bottle was used as a safe calculation for the fill height. The possible uptake of oxygen is determined by the fill space and permeability by the screwcap. The former may be limited by using carbon dioxide, nitrogen gas or liquid oxygen to displace the oxygen. After bottling, cartons should not be stacked higher than three pallets, to limit unnecessary pressure on the screwcaps. Most suppliers of screwcaps also recommend that the torque required to remove a screwcap be tested regularly. It is equally important to test the tightness of the seal regularly (Work, 2005).
New Zealand can undoubtedly be regarded as the birthplace and home of screwcaps for wines. In less than 4 years it became the standard bottle closure for wine. Local critics of screwcaps contended that wines with such a closure display more sulphury flavours, while other panels claimed the exact opposite. It is not commonly known that screwcaps also allow oxygen to come into contact with the wine, although this occurs to a considerably lesser extent than with natural cork (Tudor, 2005).
Advocates of screwcaps contend that the elimination of cork taint and unpredictable oxidation in wines that were thus bottled, has made screwcaps the standard closure for wines against which all other closures should be measured (Jalfon, 2005).
Hawkes, G. 2005. The Screwcap Initiative. Vineyard & Winery Management. July/August 2005: 44 – 50.
Jalfon, J. 2005. Screwcap pioneer poses questions. Australian & New Zealand Grapegrower & Winemaker. March 2005: 82.
Phillips, C. 2005. The Science of Closures. Wine Business Monthly. September 2005: 16 – 23.
Tudor, P. 2005. Is This The Closure For Your Wine- Wine Business Monthly. July 2005: 16 – 24.
Work, H. 2005. Bottling Under Screwcaps. Quality control issues for premium wines. Practical Winery and Vineyard 27 (3): 33 – 48.