Factors to Consider When Processing Canned Products

The system used to identify the lid is determined by the food manufacturer and is based on the granularity it needs to identify the product. What if you knew how to trace the product that was in question, but you issued the same code for it for the entire pack season? How would you know what was good and what was a potentially unsafe product? As a solution, food producers developed embossed codes to determine the food product and within what lot code (generally related to time frame) the food product was produced in. What defines a “lot” of food product? A rough definition from the food agency to the producer is, “How much food product are you willing to lose if we ask you to recall it and destroy it because we say it is unsafe for the general public?” The code system was developed to narrowly define a product lot in that situation. Emboss codes relied on skilled employees who could line up the “dies” used to punch the codes in the metal lids without misalignment, which could lead to a breach in the hermetic seal of the food container.

Problem Areas

The Grocery Manufacturers Association, or GMA, regularly receives cans from members seeking analysis of potential issues. GMA has identified several critical areas on a metal can that could be potential sites for failure; several are the responsibility of the can manufacturer. The can manufacturer not only produces the metal can body, but also both metal lids, one of which it seals on the can body as a base. The food producer has the responsibility of seaming the open end of the can with the lid provided by the can manufacturer. Assuming that there are no structural defects in the tinplate metal used to make the can body and lids, there are four critical areas for potential leakage sites: the can manufacturer’s double seamed lid, the food producer’s double seamed lid, the embossed code, and the side seam (soldered or welded).

There are several ways to reduce the number of critical areas. One way is to replace the emboss code system and use an inkjet coding system. Ink codes will eliminate one potential leakage site on the container. They can be readily changed and provide more information that can further define lot codes in case something bad happens. However, sometimes the ink codes are hard to read, smudged, illegible, or missed on fast moving lines. Cans might also be inverted prior to coding, which then makes it hard to differentiate the can manufacturer’s lid from the food producer’s lid.

The invention of the two-piece can further eliminated potential leak sites on containers. One type of two-piece can is the drawn and ironed (D&I), which is mainly used for aluminum cans and the carbonated beverage industry. Internal pressure of the carbonation is needed to keep the shape of the D&I container. The walls of the D&I container body are too weak to withstand the pressure exerted during thermal processing and subsequent vacuum formation during cooling of a typical heat process for a food product. Drawn and re-drawn (DRD) cans use thicker, stronger (tinplate) metal and can be used for heat processing foods. The solid can body and base eliminates one double seamed lid and the entire side seam. It also takes the guessing out of who put the one double seamed lid on the container.

Making Improvements

Chances are that the average consumer is not going to care if a metal container is two-piece versus three-piece. The average consumer is more likely interested in the convenience that the metal can provides. A major convenience factor is the presence of an easy open end (EZO) that does not require a can opener. The EZO has been around for a while and started with the aluminum beverage can. Early EZO tabs were designed to tear off of the lid and be discarded. The consumer did not need a tool for punching holes on the lid. However, trouble came from all the discarded sharp tabs not making their way to a proper receptacle. In 1990, the EZO system was improved with the eco-tab that allows the easy opening of the container by a ring and the retention of the metal ring on the lid.