ABSTRACT
Today, we understand the engineering, microbiology, and design factors for many and varied continuous ¥ow traditional thermal systems. The basic concepts associated with residence time, fastest ¥uid element, and thermal inactivation kinetics of pathogens and their spores are well understood. The …rst edition of this text covered these topics well. Except for the United States, many countries have moved into processing products with particulates under aseptic continuous ¥ow for well over 40 years. The self-regulating standards for most of the world meant
products could be processed and packaged aseptically but often yielded a low quality product. Uniformity of the particulate distribution varied from package to package but has improved signi…cantly in recent years. Overprocessing is still a major issue. As with any thermal treatment, the challenge has always been to identify and validate the worst case. This would be the ¥uid element in a homogeneous ¥owing system receiving the least heat treatment. With this identi…cation the system design accounts for this “cold spot” and provides commercial sterility to this element with all other elements receiving a greater treatment. As industry moved into products with particulates two common heat exchangers were used and are still the units of choice throughout the world-scraped surface heat exchangers and tube-in-tube systems. Due to the low rate of heat exchange from the carrier ¥uid to the particles both systems dramatically overprocessed the ¥uid and the smaller particles. Even the larger particles had their outer surfaces dramatically overprocessed in order to ensure that the center of the particle received at least a 12D process. To validate the treatment alginate cubes were designed with a known bioload. Biovalidation had served the canning industry and the aseptic …ller industry, and it was looked at as being useful for this challenge as well. Issues related to particle insertion, collection, and leaching of the organisms continued to be in doubt in most processes, so more heat or increased residence times were incorporated to overcome the lack of real validation knowledge for the self-regulating industry.
