To borrow the language of prize fighting, if food sterilization is a KO, then pasteurization is a TKO — germs and viruses may be dazed and confused, but some will get off the mat and live to fight another day.
Both commercial sterilization and pasteurization are used for food preservation, of course, and both rely on thermal treatment to inactivate all or most bacteria, spoilage organisms and enzymes that degrade products over time. The difference is that sterilization destroys spore formers and renders food shelf stable but also degrades a product’s nutritional value.
With interest in healthy eating growing, that tradeoff tilts the balance in favor of pasteurization, particularly in North America, where a well-established cold chain can maintain product temperatures below 40°F from the point of processing to home consumption.
Dialing down pasteurization’s thermal input would result in even more nutritional foods and beverages with longer shelf lives. Food scientists have researched numerous novel technologies that promise effective but gentle pasteurization: radio frequency, ultraviolet treatment, pulsed electric fields and ultrafiltration, to name a few. The most viable, however, is high-pressure processing (HPP), the now-industrially hardened technology that uses hydrostatic pressure in the 87,000 psi range to essentially squeeze the life out of microbes and viruses without affecting the food itself.
To distinguish HPP from conventional thermal pasteurization, one of the main suppliers of the technology has started referring to the process as “pascalization,” a salute to Blaise Pascal, the 17th Century physicist who lent his name to the measurement of pressure and vacuum. Pressure of the magnitude found in HPP vessels long has been used to squeeze oxygen out of high-performance metals, but it was not until the mid-1990s that the technology was used commercially in food.
The first several machines were purchased by Don Bowden, who went to market with HPP-treated guacamole under the names Avomex and then Wholly Guacamole before selling the business to Hormel in 2011. His first vessel held 17 liters of avocados and ran 20 cycles before a valve failed — then ran another 20 before failing again. Today’s machines hold up to 525 liters and vessels are guaranteed for 100,000 cycles, though valves and seals require more frequent maintenance.
Industry understanding of HPP and the 5-log bacterial reduction it delivers has grown enormously, particularly in North America, where the majority of operating systems can be found. As recently as six years ago, food professionals who visited Bowden’s operation wrestled with process fundamentals.
“They want to see the bubbles coming up, and that’s not the case,” noted Fernando Portales, an engineer at Bowden’s former Fort Worth, Texas, firm. The extended shelf life and food-safety assurance delivered by the technology made the technology popular for ready-to-eat meats, which until recent years accounted for the majority of applications. Now HPP is being applied to wet salads, juices and beverages such as coconut water, where flavor improvements over aseptic processes are driving sales gains.
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Declining operating costs for HPP are drawing scores of processors to the technology. Most of the world’s installed base of approximately 300 presses are in North America, either as tolling services or a combination of own-product and third-party processing to fill up production schedules.
As the core systems become more robust, improvement efforts have shifted toward more efficient loading and unloading and expansion of packaging options.
When Sandridge Food Corp., Medina, Ohio, commissioned its first HPP press in 2010, it also installed a packaging line to fill inner-seal containers. Rigid cups with snap-on seals still are used for coleslaw and other wet salads that are not HPP processed, but those container lids don’t survive high pressure.
A second HPP unit came on line last fall, and pouched products like Sandridge’s new Layered Selections of minimally processed medleys such as black-eyed peas, couscous and corn are being pasteurized. Inner-seal cups continue to be used, as well.
“Pouches work great,” asserts John Becker, Sandridge’s senior director-marketing, but the firm would like more options. “More and more packaging companies are seeing the need (for HPP-compatible containers) and are addressing it.”
Sandridge’s machines were fabricated by Hiperbaric, a Spanish firm with offices in Miami. All North American presses currently operating were built either by Hiperbaric or Avure Technologies Inc., a Middletown, Ohio, company that was spun off from HPP pioneer Flow Technology in 2005. Flow partnered with ABB in Sweden in the 1990s to make the first commercial HPP units.
A third supplier will be entering the market soon, and it is focusing on packaging options. Multivac Inc. partnered with Thysen Krupp Group, another German company, to develop highly automated HPP systems. Thysen Krupp’s Uhde Technologies division builds the HPP unit, while Multivac concentrates on the packaging side. Stepping outside its vacuum-pack comfort zone, Multivac is pursuing MAP packaging that can withstand high pressure.
According to Multivac’s Ben Eastman, a 350-liter HPP system has been delivered to a Mexico City meat processor, with integrated product filling to case packing components. A fall start-up of the system is anticipated.