Food Protection Trends - July/August 2024 - 274

for each type of finish, allowing manufacturers and suppliers
to work with a variety of containers while maintaining the
integrity of the finish and closure. The metal closures or lids
are commonly made from tinplated steel or tin-free steel,
depending on the type of food product packaged. For further
protection of the metal under corrosive conditions, such as
when packing acidic foods, organic coatings may be applied
to the internal and external surfaces of the caps. The coating
must be compatible with the food and enable the application
of the plastisol gasket material (3).
The lug closure, also known as twist cap, is widely used in
the food industry because of the high speed achieved during
application, because this lid needs only a partial turn. The lid
provides a secure hermetic seal that can be opened by hand
and resealed by the consumer for further use. The lids have
a metal shell with a straight or fluted skirt and may have a
safety button (3). Depending on the type of lid, there can
be three to eight lugs that engage with the glass lugs of the
container, and the lid diameter ranges from 27 to 110 mm.
The lids are lined with plastisol to provide a hermetic seal
that can hold a vacuum. The closures need to be inspected at
regular intervals to ensure the integrity of the seals (2).
Based on U.S. Food and Drug Administration canning
regulations (11), shelf-stable, hermetically sealed food
containers must be inspected to ensure seal integrity. For
glass jars, the inspection program should include a visual
examination and a destructive (tear down) examination for
defects that could affect product and/or package integrity.
The visual examination should be made at intervals not >30
min, and the destructive evaluations should be conducted
at intervals not >4 h. Visual examinations for lug closures
include checking for obvious defects, misapplication of cap,
lid concavity indicating vacuum, and pull-up. Pull-up is a
visual check to measure the fit of the closure lugs on the lugs
of the glass jar and is defined as the " distance between the
leading edge of the cap lug and the vertical neck ring seam
on the glass finish " (3). Destructive evaluations include
measurement of vacuum, fill temperature, headspace, gasket
impression, removal torque, and security. Security, defined as
the lug tension of an applied closure, is the most dependable
measurement to ensure a good seal for lug closures. Adequate
pull-up and security values per type of container are specified
by the closure manufacturer (2).
For canned foods packaged in glass containers with metal
lids, the presence of vacuum ensures that a hermetic seal
has been achieved. A visual indication of vacuum to the
consumer is the depressed safety button, located in the
center of the lid, which also helps to indicate low- or novacuum
packages in automatic operations (1). The factors
affecting vacuum formation are headspace, product sealing
temperature, air in the product, and capper vacuum efficiency
when cappers are used. The required headspace differs
with the type of product, but a general rule of thumb is 6 to
10% of the container volume. Keeping all the other factors
274 Food Protection Trends July/August
constant, the higher the product temperature is at the time
of sealing, the stronger the vacuum will be after cooling. The
air in the product should be kept at a minimum to ensure a
good seal, product appearance, and product quality because
oxygen in the air will accelerate rancidity, browning, and loss
of nutrients (3).
The standard lug type metal lids made of steel can be
hard to open; thus, a new generation of aluminum lids was
developed with a push button (Fig. 1). The consumer applies
a firm push to the button located at the top of the lid to
release the vacuum in the container, thereby significantly
reducing the torque required to open the lid. The aluminum
lid was designed with the required strength to maintain
closure integrity throughout the shelf life of the packaged
food. If vacuum were accidentally lost, the lid would lose
concavity, similar to standard lug lids, indicating to the
consumer that the seal is compromised. The new vacuum
release aluminum (VRA) lug lids were designed to facilitate
opening of a glass jar by all consumers, including the elderly
and physically impaired individuals (4). One of the main
markets for glass jars is the tomato sauce industry. According
to a report by Grand View Research (6), the global pasta
sauce market is valued at USD 13.47 billion and is expected
to grow at an annual rate of 3.2% from 2020 to 2027. This
market segment is one of the main users of glass closures and
must have packaging that is sustainable and inclusive.
This study was focused on evaluating the performance of
VRA lug lids versus standard lug lids to render hermetically
sealed glass jars. To assess the proper application of the new
and regular lug lids, both nondestructive and destructive
tests were performed. The closure integrity on jars filled with
deionized water was tested by measuring pull-up, vacuum,
removal torque, and security. Main factors affecting vacuum
formation, such as hot-pack temperature and headspace, were
studied. Jars packed with tomato sauce and capped with both
lids also were evaluated for ease of opening by measuring
removal torque.
MATERIALS AND METHODS
Sample preparation
Glass jars (24 oz 710 ml) with lug finish and standard
lug lids (63 mm in diameter) with plastisol lining were
obtained from Giovanni Foods (Baldwinsville, NY). VRA
lug lids of the same diameter were obtained from Consumer
Convenience Technologies (EEASY Lids, Dayton, OH).
Both standard and VRA lug lids had the same number of
metal lugs and same plastisol lining materials, as shown in
Figure 1.
Sample jars were prepared based on the procedures
listed in Figure 2. Jars were filled leaving either 6 or 10%
headspace. The headspace was calculated using the weightby-weight
method. The weight of the glass jar was 329 ± 1 g,
as determined with a scale (model 12007333; Sartorius Ag,
Gottingen, Germany). When filled with deionized water up
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