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
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
• Closure Robustness
The true quality of a wine closure
is shown when it is submitted to abusive
conditions while delivering the
not only can occur as a consequence
of the bottling event, but
also during final product storage and
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
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