Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
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It is sometimes difficult to report a discrete OTR value for screw caps (Saranex™ and Saran/Tin) as product specification. In this respect, it is more appropriate to report a range of OTR values. Nevertheless, if proper QA procedures are in place, screw cap application should provide expected product consistency within a bottling event.
• Closure Application
Equipment for natural cork (which can also be employed for technical cork and synthetic closures) has been available for years, so technical assistance is easy to find when adjustments and repairs are necessary.
In contrast to the equipment built for insertable closures (naturals, technicals, and synthetics), the entrance of screw cap machinery into the wine industry is fairly recent and carries a higher degree of technical sophistication. Head block, thread, and skirt roller pressures, type and height of rollers, and exact dimensions and angles of glass bottle design in relation to the dimensions of the aluminum screw cap are all important factors to observe in order to achieve desired bottling results.
There are differences in performance across the range of natural corks and synthetic closures. Hence it is important that bottling conditions are optimized for each closure type. Otherwise issues such as “suck ins,” “push outs,” and leakage can occur. Improperly maintained equipment (particularly corker jaws) can result in closure damage during bottling leading to leakage and other problems.
Screw cap equipment is not only costly, but requires exact precision during application. Screw cap equipment with improper settings can not only lead to ugly external applications, but seriously compromise the sealing specifications of the delicate top liner. To make things more complex, these mistakes might not be apparent on bottling day but later during product storage. However, like other critical characteristics, these specifications can generally be controlled with good bottling QA protocols.
• Closure Robustness
The true quality of a wine closure is shown when it is submitted to abusive conditions while delivering the expected results. Specification deviation not only can occur as a consequence of the bottling event, but also during final product storage and transportation.
Proper bottling temperature, fill height (ullage), and final headspace pressure all need to conform to the specifications of each closure/bottle combination. In the case of inserted closures (natural cork, technical cork, and synthetic closure), appropriate bottle neck diameter and taper are required for an optimum seal.
Periodically, glass bottles with unexpected neck tapers appear in the market. These bottles can seriously affect the seal of some of the longer-length corks, resulting in closures with no or very low compression values at the bottom end, which can cause cork wicking.
It is always advisable to confirm neck diameter and taper with a bottle neck profile analysis. In the case of screw caps, besides the potential defects outlined under closure application, it is important to procure glass bottles with even neck rims and no top surface imperfections; otherwise partial liner compression and cut-through could occur.
If expansion due to elevated wine temperatures during distribution exceeds the headspace volume, seal failure will occur. When wine bottles are stored and/or transported at higher than recommended temperatures, natural cork typically shows signs of wicking or leaking, while synthetic closures often push up or leak. Bottles closed with screw caps require extra care during industrial handling so the top part/circumference is not dented. If so, the seal of the liner could be compromised, resulting in random premature wine oxidation.
• Environmental Considerations
One final consideration is the impact of the closure on the environment. Recently, this impact has been measured as the carbon footprint contributed by one (or one million) unit(s). Studies have indicated that the carbon footprint values of different closure categories claim varying results. However, it is generally accepted that natural corks contribute the least, followed by synthetic closures, and technical corks, with screw caps contributing significantly more.14,15
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12. Cork Supply USA (Internal Data).
13. Peck, Jim. G3 Enterprises (personal communication) 2009.
14. Forgues, C. September 2007 “Carbon Appraisal of the Different Methods Used for Closing Still Wines.” Aust. & New Zealand Grapegrower & Winemaker, 524.
15. Walker, L. August 2007 “Cork and Sustainability.” Wines & Vines.