Winery (Oakville, CA) offered premium Cabernet Sauvignon in bottles
sealed with screwcaps in the late 1990s. Since then, PlumpJacks
continued success has opened a lot of eyes, and the premium wine
industry has begun to consider use of screwcaps.
Another winery shifting to screwcaps is Hogue Cellars (Prosser,
WA). David Forsyth (director of winemaking) stated in June 2004
(after completing a 2 1/2-year closure study), Bottling our
wines with screwcaps will yield tremendous benefits: elimination
of cork taint, consistent and appropriate ageing, lower SO2
levels at bottling, and greater ease in opening bottles.
Screwcaps, however, are not new. Threaded aluminum ROTE (Roll-on,
tamper-evident) or ROPP (Roll-on, pilfer-proof) closures were introduced
in the 1960s. Researchers at Dow Chemical in 1933 discovered polyvinylidene
chloride, the main material in the liner-seal that is in contact
with wine, subsequently branded as Saran and Saranex
(Saran sandwiched between layers of polyethlylene or polyethylene-vinylacetate).
When a tin/saran liner is used, it is the tin layer that creates
a barrier to oxygen ingress.
Wineries such as E&J Gallo (Modesto, CA) have been producing
wines with screwcap in their economy and beverage categories for
more than 30 years, notes Mary Wagner, chief technical officer.
In Finland, Norway, Sweden, and Switzerland, wine under screwcap
has been popular for more than 30 years, reports George Thomson
(Crown Cork/United Closures & Plastics [UCP] in the United Kingdom).
With an increasing demand for screwcaps, more suppliers are entering
the marketplace. This report will examine quality control factors
and standards for the three critical legs in screwcap usage: screwcap
suppliers and manufacturers, critical factors in glass bottles,
and screwcap application at bottling.
Suppliers / Manufacturers
Pechiney (now Alcan Packaging), with its Stelvin brand, was one
of the first suppliers to offer a long skirt (30mm x 60 mm) screwcap
for premium wines. Scott Laboratories offers the Alplast brand.
More recent entries are Cork Supply USA with SAVin from Metal Closures
Group in South Africa, Oeneo Closures (formerly Sabaté) with
the S-Cap, G-3 Enterprises (exclusive U.S. manufacturer of Royal
90), Richards Packaging (representing Crown Cork/UCP),
Alcoa, Auscap (Australia), and the Guala Closures Group.
Some of these suppliers are divisions of larger international closure
groups, while others contract to have screwcaps made to their specifications.
In most cases, the fabrication plants are already making closures
for other food and beverage industries and abide by, or utilize,
several quality control certifications.
Certifications include ISO-9000 (certified by the International
Organization for Standardization), HACCP (Hazard Analysis and Critical
Control Point) typically used for food and food product production,
American FDA compliance, and European regulations, including those
applicable to the use of heavy metals. Ask your supplier for current
confirmation of these certifications.
Closure liners must comply with U.S. FDA CFR 21 reg. 177.1210
and the internal coatings must comply with U.S. FDA CFR 21 reg.
175.300, explains George Crochiere, Crochiere & Associates,
packaging consultants, (Pepperell, MA). Compliance does not
guarantee good flavor, sealing, or barrier properties.
While certifications and compliance activities are not an iron-clad
guarantee against defects, they certainly minimize problems. Many
winemakers agree with the assessment of Aron Hess, executive winemaker
at Rex Hill, (Newburg, OR), who suggests that the few problems he
has experienced have generally not been the fault of the cap manufacturer.
Wineries should only obtain closures from manufacturers who
produce screwcaps under statistical process control, notes
Thomson (Crown Cork/UCP).
Manufacturing of screwcaps
The manufacturing of aluminum screwcaps starts with the coating
or painting process, says Crochiere. The flat aluminum
sheet has a total of two to five individual coatings applied to
the inside and outside. The coatings provide corrosion protection,
lubricity for manufacturing and removal torques, improved adhesion
for the inks, and decorative color.
The aluminum is cut into discs and drawn into the closure
shape. Depending on the cap and process, this is accomplished in
one to three operations; the result is a cap shell with smooth sides.
If the cap is to have decoration or a logo applied, this is
done next with inks and a clear protective varnish. In this process,
each cap is handled, registered, and printed individually whereas
short screwcaps (used on beer or water) are typically printed during
the coating process.
The last metal operation trims the cap to its specified length,
applies the knurling and liner-retaining feature, and makes the
cuts for the pilfer-band bridges (breakaway feature).
The final manufacturing process is insertion of a liner; these
are either provided as cut discs or as a roll of material that is
cut in the insertion process.
The screwcap manufacturer conducts quality checks at each
stage of this process. Final quality control process should include
but not be limited to: closure application, sealing, pilferband
operation, removal torques, correct liner material, and coating
and ink application, color, placement and adhesion.
Seal manufacturing processes
The actual sealing discs, and their layered materials, are normally
made by companies other than the cap manufacturer. The seal material
is made by a combination of extrusion, co-extrusion and/or lamination
processes. The material is shipped to the cap manufacturer either
in sheets, which the cap manufacturer cuts to size as they are inserted
into the cap, or as pre-cut discs to save on shipping and scrap
It is important to understand the potential areas for contamination
in the supply chain of screwcaps and liners. As noted, the seals
are normally manufactured in different plants from where the screwcap
Trucks and containers carry all sorts of products and chemicals
(some of them volatile), which could be absorbed by the plastics.
Again, as part of the cap manufacturing process, inspection of incoming
raw materials should be part of the quality control process. (More
on this in the Bottling line application section below.)
Sealing material options / selection
Seals are made to provide a compromise of resilient softness
for sealing properties and barrier properties, says Crochiere,
to minimize oxygen ingress, carbonation loss, loss of volatiles
and flavor neutrality; typically these are opposing properties for
polymers. Seals are made in three different ways; formed in place
PVC, single material discs, and multi-layer discs of resilient cushion
layers and barrier material layers.
The oxygen transmission rate for Saranex is only slightly
greater than tin-saran or aluminum-saran, says Jim Peck, G-3
Enterprises (Modesto, CA).
Each sealant material and configuration has its own sealing,
flavor, and barrier properties, adds Crochiere. Changes
in closure and/or liner supply should be carefully evaluated. In
addition to the sealant material, the closing conditions also affect
the barrier properties as different closing conditions can increase
the length and reliability of the seal on the bottle.
Based on work started in the beer industry in 1982, the sealant
industry has developed barrier materials and techniques to evaluate
them under commercial conditions for oxygen ingress, carbonation
loss, and the ingress of TCA, TeCA, and other undesirable contaminants.
The methods are now being used for wine packaging.
An oxygen permeability coefficient will tell you how many
micro-grams of oxygen permeate through a given package component
per day. Combined with the volume of the package, an ingress rate
in ppb of total package oxygen per day for a closure/liner type,
closing condition and bottle size can be determined. These units
are the same as those used to measure oxygen levels at filling and
can be added together to determine the total oxygen in the package
from filling and ingress over time. Versions of this test are also
used to evaluate the performance of closures when exposed to abuses
like warehouse stacking, transportation, temperature changes, or
impact on the closure.
Another term for oxygen permeability coefficient is oxygen
transmission rate, which would include not only permeation but any
micro-leakage, notes Jim Peck.
When selecting a new closure and liner, a comparison of oxygen
ingress coefficients or rates to existing closure types will help
predict the shelf-life and development of the wine with the new
closure, adds Crochiere. In addition, comparison of
TCA or TeCA barrier properties can minimize the risk of cellar or
transportation contamination. Typically, the better the barrier
properties, the higher the cost.
A chart of oxygen permeability coefficients for some typical
wine closures is in Table I. These numbers have been generated from
numerous tests over the past seven years and should only be used
as an indication of what is possible.
The choice between Saran/Tin or Saranex seals generally reflects
the winemakers decision on whether to seal the bottle completely
for a short-lived wine, such as Sauvignon Blanc, Riesling, or Pinot
Grigio, or to allow some permeability, for ageing red wines. However,
both Patrick Pickett, (winemaker for Pepi, Oakville, CA), and Aron
Hess, have observed relatively little difference in the actual taste
of wines using either of these two seal types with whites or reds.
It is a huge debate on how much oxygen, says Thomson
(Crown Cork/UCP). The technology is available; unfortunately
Crown Cork/UCP does not have a fix on the quantities required over
Wineries using screwcaps are trying to get a fix on
the right amount of oxygen for their various wines. Hogue uses the
Saranex seal for both red and white wines, while John Conover (general
manager at Plump Jack Winery), reports using the Saran/Tin seal
for their reds, and some of their white wines. All of which suggests
that the Saran seal for whites and Saranex seal for reds guideline
can have many exceptions.
Your supplier should have an inspection procedure for all incoming
products from its manufacturers. This should provide a second line
of defense against possible manufacturing errors. All suppliers
contacted for this report did have a receiving inspection procedure
in place. These include checks for the cap artwork and colors, that
the correct seal-disc has been properly inserted, and that the packaging
integrity has been maintained. If you are using a new supplier,
it would be worthwhile to ask what checks are included in their
The distributors inspection procedures should also include:
inspection of the packaging for damage (especially crushed contents,
but also rips and tears); any odd odors; sample inspection of the
caps to ensure they conform to size, thickness, skirt length, and
style; sampling of the seals to ensure they are the correct type
and inserted correctly (since the layers in the saran/tin-type seals
are not symmetrical, they must be inserted with the saran side to
face the wine); proper printing, and embossing. Colors should match
between the top and skirt (they are printed separately), and should
match the customers specifications. Break points (bridge line)
must be properly perforated; and general cleanliness of the caps
and their packaging must be assured.
Screwcaps and glass bottles
Not all screwcaps are compatible with all styles of glass bottles,
and vice-versa. The bottle finish design and corresponding neck
diameter must be compatible with the screwcap and closing equipment.
Cap manufacturers and distributors want to inspect a bottle sample
the winery proposes to use to make sure their cap will fit properly,
or can supply design specifications for a glass manufacturer. Aron
Hess emphasizes: Screwcap manufacturers who do not insist
on matching their cap to a specific bottle/finish tend to supply
more problematical caps.
This problem was echoed by another winemaker, Tony Bish (Sacred Hill
Wines in Hawkes Bay, New Zealand), who received a shipment of
bottles with a slightly elliptical neck, some outside the range of
specifications. The screwcap would not fully descend onto the bottle.
The capping head would come down and impact the closure and tighten
onto the bottle, resulting in many broken bridges on the cap, compromising
the tamper-proofing aspects. The caps did seal correctly, but the
result was unsatisfactory due to sharp edges where bridges were broken
and unsightly appearance.
A different brand of screwcap worked better, because the caps had
a slightly wider skirt to allow more caps to fully seat on the bottle-neck
before the capping head was applied. Also, the inside surface of
the caps was smoother and the reduced friction allowed caps to seat
better. However, since the bottles were out-of-round due to forming
irregularities, even this did not fully correct the problem.
The Sacred Hill problem was only solved by disgorging some bottles
and re-bottling in new bottles within specifications. Given the
tight tolerances required for a proper seal and tamper-proofing,
all screwcap suppliers and winemakers recommend that great effort
be taken to ensure that the screwcap and glass bottle styles be
Richards Packaging has had several experiences with matching
of bottle and closure, reports Bob Boord. The Glass
Packaging Institute (GPI) provides neck finish specifications, but
many small deviations have crept into bottle neck finishes over
the years. In addition, molds wear. The result is that constant
attention needs to be given to the proper matching up of neck finishes
on bottles with the closure specifications.
In one situation, a customer used seven different glass bottles.
Analysis found that there were seven variations of the GPI neck
finish, and some of those deviations were serious. In another situation,
a glass manufacturer built new neck finish inserts, but the new
specifications changed the fit of the closure on the bottle.
Manufacturers of bottles and closures do not communicate well
with each other, so it becomes important for the winery-buyer and
the distributor salesperson to work together to provide bottle samples
to the closure manufacturer for testing to assure good fit. Whenever
a new bottle is introduced or existing bottle molds are rebuilt
or modified, samples of all cavities should be sent to the screwcap
manufacturer for analysis.
The actual sealing of the screwcap is achieved at the top of the
outside rim radius of the glass bottle. Therefore, this rim must
be smooth and correctly curved. The glass thread must start a specified
distance below this rim to accommodate the seal.
The holding power of the cap is achieved by the threads, while
the pilfer-band locks the cap in place, explains Crochiere.
In addition to the proper surfacing at the top edge, the thread
and pilfer band ridge below the thread tolerances are relatively
tight, thus the need for coordinating the bottle and cap specifications.
Bottling line application
Prior to and at bottling, a number of inspections and checks must
be made. Most of the caps are packaged bulk in plastic bags and
shipped in cardboard boxes. The boxes must not show any evidence
of being crushed, which could dent or deform the caps; nor should
the plastic be ripped or torn, in order to keep the caps clean and
protect them from odors. Clean, dry storage in the winery is essential.
Bottles should be inspected for straight and concentric necks
in addition to dimensional checks to insure that the sealing area,
threads, pilfer step and neck comply with specifications,
says Crochiere. Bottles should also be inspected for manufacturing
imperfections or damage (glass flash or slivers at the mold-parting
lines) that could result in unacceptable performance of the screwcap
sealing system. Dont forget to check for cleanliness and off-odors
in the bottles and cases.
Alignment of the capper is absolutely critical. Kristi Koford (winemaker
at Napa Wine Company, Oakville, CA), notes that one screwcap manufacturer
insists on inspecting the head set-up for first-time users. She
appreciates this service since they have previously experienced
a brand that wouldnt seat on the bottles and then jammed the
The capper is a complex piece of machinery with a precisely-shaped
head (pressure block) and several sets of rollers designed to mold
the screwcap in a specific manner. Precision springs apply a pressure
of around 400 lbs. force (28.12kgf/cm2) to the pressure block. This
squeezes and forms the screwcap on the bottles top sealing
edge, forming the seal. This part of the sealing is referred to
as a reform or redraw. The capper should be set to the particular
screwcap manufacturers settings.
Wineries should consult with Alcoa, Zalkin, Silgan, Arol, Bertolaso
or other capper manufacturers to determine top pressure in a capper.
There are three general types/ shapes of pressure blocks,
explains Crochiere: 1) a flat surface that produces a top
seal only, 2) a partial or slight curved block that produces a slight
corner seal, and 3) a full reform that draws or wraps the closure
and liner around the top of the glass and seals 1.5 to 2.0 mm down
the outside of the bottle.
The rollers that form the threads need to be exactly aligned and
moving at a speed that will allow them to be inserted and released
at the proper time.
Steve Rasmussen (owner of S.L.O. Bottling Services), notes that
the capper head needs to move slow enough in order to allow these
rollers to accurately form the threads. If speed is essential, more
heads should be installed.
The second set of rollers simultaneously crimps (undertucks) the
aluminum closure under the pilfer ring and smooths the skirt to
complete the seal and hold the cap in place. The head and screwcap
manufacturers recommend specific pressures for each of these sets
Another important factor is the head space to allow for wine expansion
without creating excessive internal pressure in the sealed bottle.
Generally, screwcap manufacturers suggest around 2% of the wine
volume. This fill level should be checked periodically throughout
the bottling process.
As more winemakers become familiar with using screwcaps, one current
debate is on sparging with either nitrogen or CO2
prior to cap placement, to displace any oxygen. Some winemakers and
bottling line companies use nitrogen gas, while others are using liquid
nitrogen. Patrick Pickett (Pepi Wines), uses liquid nitrogen that
requires little time to displace the oxygen.
The total packaging oxygen (TPO) exposure to the wine is
the sum of the oxygen pickup during transfer to the filler,
explains Crochiere, pickup as the wine is being filled into
the bottle, the oxygen added from the head space, and the oxygen
ingress through the package (closure) during the life of the product.
Typically the two largest contributors are the head space and the
Figure I illustrates the amount of oxygen added to the filled product
as a function of volume of head space. The chart shows two relationships,
one with a complete flush as with liquid nitrogen, the other with
If you use inert gas, adds Crochiere, the head
space flush will not be as thorough due to air turbulence and allowed
time. When using liquid nitrogen, there should be excess added so
that bottles are sealed with 10 to 15 psi nitrogen pressure.
Selection of the sealing liner and optimum reform will minimize
ingress as illustrated by the oxygen permeability coefficients and
ingress rates in Table I. The use of inert gas to flush the empty
bottle before filling (with or without alternating vacuum) would
optimize the filling line for minimum oxygen pickup.
David Wright, production manager for Pacific Wine Partners (Gonzales,
CA), uses CO2 which, being heavier, displaces
oxygen. Hogue Cellars quality supervisor, Mei Yeung, notes
that because screwcaps allow for relatively large head space, when
compared to cork closures, the use of nitrogen, carbon dioxide,
or argon is necessary to remove the oxygen from that space. Hogue
uses liquid nitrogen. On the bottling line, the gas (regardless
of type), is delivered just after filling and before cap application.
Quality control of the caps does vary. Jose Mendez, the bottling
line supervisor for Ultima Mobile Bottling, has, on occasion, seen
a difference in skirt lengths of 1 to 2 millimeters. The longer
ones can block the cap feed. He also watches for the seal discs
falling out of caps as they move through the cap feeding system.
After bottling, case storage is recommended at no more than three
pallets high, in order to prevent excessive compression on the caps.
PlumpJack Winery solves the problem by shipping bottles horizontally
in six-bottle wooden boxes. Hogue Cellars stores screwcapped wine
without pallets four-cases high for even distribution of vertical
Testing on bottling line
As a basic method to ensure that bottles are properly sealed, most
suppliers recommend periodic testing of the torque required to remove
a screwcap. Several supply a torque tester to accurately and easily
perform this test. Frequency of this testing is up to the winery,
although one bottle, every one to two hours per capper being used,
is a commonly mentioned standard.
Wright suggests that the torque specifications should be in the
range of 5 to 15 inch-pounds. The test is conducted with two twists.
The initial twist breaks the seal and should be on the higher side
of the range. The second breaks the aluminum bridges
connecting the threaded portion to the lower skirt, and should be
no less than the lower number in the range. (Normally the wine consumer
would unseal and break the bridges with one motion.)
A pressure test is used by Wright to test the seal. This consists
of injecting CO2, to apply pressure into the
bottle via a threaded needle, while the bottle is under water. As
the pressure is increased, an operator watches for bubbles escaping
from under the cap. Normally the cap should hold a minimum of 20
lbs/in2 of pressure for still wines. Wright
emphasizes, This is an important test as the internal pressure
in the head space of a bottle can vary drastically due to elevation
and temperature changes.
The Secure Seal Test (pressure test) injects any pressurized
gas at a controlled rate into the bottle via a threaded piercing
needle, says Crochiere. The specification of 150 psi
is for carbonated soft drinks, beers should hold about 100 psi,
still products like wine only need a closure that holds 40 to 50
psi. This is the force required to compress the liner material and
allow the air to vent. A closure that is applied incorrectly can
leak at very low pressures.
Several companies supply testing equipment for these checks. Contact
your screwcap supplier or these testing equipment suppliers: Secure
Pak or Dillon.
Additionally, a bottling line worker should make a visual inspection
of the caps; noting the smoothness of the threads, any deformation
or bulges at the top, and a clean crimp line. When the top of the
cap is removed, it should separate cleanly at the bridges,
with no torn or sharp edges to cut the openers fingers.
Inspection should also include the coatings and inks
the more decorated the cap, the more likely there will be paint
and ink dust generated in the screwcap hopper, adds Crochiere.
This can be unsightly, but more important, the dust will collect
inside the caps and contaminate the wine. In addition, check for
coating lifting at the cut edges of the pilfer bridges and the bottom
of the cap. Dark color caps show scratches much more than light
color caps as the exposed aluminum makes a sharp contrast.
issues for further research
In 1999, Peter Godden and colleagues at the Australian Wine Research
Institute (AWRI) undertook an extensive research project on closures
for wine bottles including the use of corks, synthetic corks,
and screwcaps. One result of their testing was that screwcaps showed
the least reduction in free SO2 of all closures
Having noted a similar maintenance of SO2
levels by screwcaps, several winemakers interviewed for this article
including Shaun Richardson, vice president and winemaker at Clos
Pegase (Calistoga, CA), are looking into the possibility of reducing
the SO2 level at bottling.
However, the AWRI closure research project also indicated, through
sensory testing, that the screwcap closure had the highest reduced
aroma. It was described as struck flint or rubbery.1
The authors reporting the study subsequently note that, after 36
months in the bottle, the same wine sealed with the corks also exhibited
similar aromas. Further exploration of the causes and/or relation
between the SO2 levels and reduced aromas
issues will be required.
Perhaps associated with this reduction are the yet-to-be totally
defined differences in permeability of sealing materials in discs
of various screwcap brands. While Conover indicated that he does
not want breathability with the PlumpJack Cabernets and hence uses
the Saran/Tin seal, Richardson uses the Saran/Tin for the Clos Pegase
Sauvignon Blanc wines, and Saranex disc seals for the Chardonnay,
in order to allow some oxygenation during ageing. The jury appears
to still be out on the issues of seals and wine type, with more
experimentation and experience necessary.
Screwcaps have a history of use in many industries. They are relatively
new as a premium wine closure, but have a long history of use with
low-priced wines. The technology and materials are well-tested and
appear to be suitable for wine. If winemakers make sure their caps
and glass are compatible, are cautious with new suppliers, and test
frequently with the first bottlings, screwcaps should have a positive
impact on wine, by providing, as Patrick Pickett notes, consistency
bottle to bottle.
- Francis, L., J. Field, M. Gishen, A. Coulter,
P. Valente, K. Lattey, P. Høj, E. Robinson, P. Godden.
(2003, August). The AWRI closure trial: sensory evaluation
data 36 months after bottling. Australian & New
Zealand Grapegrower & Winemaker, 475, 5964.
- Godden, P., L. Francis, J. Field, M. Gishen,
A. Coulter, P. Valente, P. Høj, E. Robinson. (2001,
September). Results of an AWRI trial investigating
the technical performance of various types of wine closure:
Part II Wine composition up to 20 months post-bottling.
Australian Grapegrower & Winemaker, 452, 8998