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A Look at Metal Lug Closures

Also known as lug lids, lug caps, and twist caps, lug closures are the choice for a variety of products that are heat-processed and hot-filled in glass jars.

Sterling Anthony

Lugs are the equally spaced tabs around the skirt (under-rim) of the closure. Their purpose is to interlock with the interrupted tread of the container’s finish (neck). Due to that interlocking, lug closures can be applied or removed with less than a full turn. Continuous-tread (C-T) closures, by contrast, interlock with the continuous thread of the container’s finish and require at least a full turn to apply or remove.

On the inside of lug closures is a compound (typically plastisol), essential in effecting a hermetic seal. When the closure is applied, the compound compresses around the lip (land) of the container, filling any void between the container’s lip and the underside of the closure.

Heat-processed high-acid foods, such as sauces, soups, marinades, and jams/jellies/preserves, are heat-processed, hot-filled into glass jars, and crowned with lug closures. Processing, filling, and capping are components of a system for producing shelf-stable products. Processing and filling must be done under strictly controlled temperature setting to destroy harmful microorganisms. After that, the lug closure becomes the main agent in maintaining shelf-stability until the container is opened.

Lug closures fulfill all the functions of packaging: containment/protection, communication, and convenience/utility. Containment/protection has been addressed by preceding comments. Communication can be had with printing on the top and around the side, conveying brand name, product line variety, and promotional claims. Also under communication is safety information, such as refrigerate after opening. Another type of safety communication warns against purchasing the product if the center-located dimple/button has popped up (which happens when the hermetic seal has been broken). Convenience/utility accrues from the twist-on-and-off feature and can be enhanced with ribbed sides for better gripping.

Given that glass containers and metal lug closures are complete barriers, the most likely cause of lost sterility is a poor seal. When experienced on a large scale, lost sterility can result in rejected shipments or even a product recall. It behooves a brand-owner, therefore, to have quality-assurance measures geared to achieving quality seals.

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INTRODUCING! The Latest Trends for All Industries at PACK EXPO Southeast