the NY Times has a long article on the Topps recall today; the last two paragraphs say:
"According to industry experts, the size of the Topps recall was probably related to the company’s practice of “carrying over” meat from one day’s production to the next, without giving the older meat a separate batch number. The practice is not in itself illegal or unsafe, the experts said, but in the event of a problem, like an identified case of E. coli, the mixing of several days’ production makes it harder for officials to know the extent of the contamination.
Michele Williams, a spokeswoman for Topps, declined to comment on whether Topps carries over meat without giving it a separate batch number. But Ms. Eamich, the Agriculture Department spokeswoman, said the company did carry over beef. "
More simply, carryover means if you have e. coli in a batch of ground beef on Monday, and you take some of Monday's batch and mix it into Tuesday's, you have now contaminated ALL of Tuesday's meat. And if you take Tuesday's and mix it into Wednesday's, that batch is now contaminated, and on and on for as long as you keep doing this. If this is standard practice, as it appears it was for Topps, a recall can stretch back indefinitely.
The phrase, "The practice is not in itself illegal or unsafe...," is a scary one. It is a sobering reminder that it is LEGAL unsafe practices like this that encourage outbreaks and mass recalls.