Extended shelf life packaging (ESL) has spawned an era where we can offer products that can be kept in consumers’ refrigerators for prolonged periods, while still maintaining their quality.

No commonly accepted definition of ESL products exists. But, in general, the ESL process is said to prolong shelf life beyond that of traditional pasteurized products. In the case of dairy products that are distributed under refrigerated conditions, ESL can provide a shelf life up to 90 days, as compared to the 10 to 28 days provided by pasteurization.

Indeed, ESL has contributed to the major reinvention of the milk category, but it has also recreated flavored milk, flavored coffee lighteners and fruit beverages, and brands like Nesquik, Tropicana and Minute Maid, which have enjoyed the benefits of their longer shelf life attributes. ESL has also generated an entirely new and highly successful category of chilled juice products.

The challenge of ESL is that it produces products that are not necessarily commercially sterile. To withstand distribution times that are long—up to 90 days during which pathogenic microorganisms might grow—ESL products require some degree of temperature control during distribution.

Low-acid products (such as milk, cream or pudding) must be distributed under refrigerated conditions that prevent microbiological growth and retain biochemical quality.

On the other hand, because high-acid products (such as fruit beverages) and their internal packaging environments can be commercially sterilized, ambient temperature distribution is often possible. Today, however, it is less common to sterilize the package interior or the packaging environment, which means most high-acid ESL packaging must still maintain chilled distribution to retard growth of spoilage microorganisms and biochemical oxidations that would otherwise damage the product.

And though packaging materials are generally not sources of microorganisms, they are often sterilized with steam, steam plus hydrogen peroxide, hydrogen peroxide, hot water or other chemical-plus-heat treatments. The key is to expose all of the interior surfaces of the package—and its closure in the case of plastic bottles—to the antimicrobial before filling.

ESL packages may be either hot or cold filled, but distribution requirements may change as a result.

In hot filling, the hot fluid product itself sterilizes the package. The result is a packaged product that is microbiologically stable under ambient temperature conditions. In cold filling, the fluid product, which is filled at ambient or below ambient temperature, is treated to reduce the microbiological load before filling. Low-acid products that are cold filled must be distributed under refrigerated conditions, but cold filled high-acid products can also be distributed under ambient temperature conditions.

A major rationale for the application of ESL is that the protocol can help prevent product quality deteriorations that often result from pasteurization or aseptic processing. Although microbiological growth may be held in check by treating the product and/or package under such systems, many products frequently experience chemical reactions like oxidation, which can lead to off-color, flavor and even mouth feel. A key advantage of ESL is that, through its downstream chilled distribution, it can help prevent impairments to product quality, which can quickly dilute the equity of a brand. BP