A New Zealand food scientist says there may be a reasonable explanation for the delay between production and Fonterra detecting the botulism-causing bacterium in whey protein concentrate.
Dr John Brooks is a microbiologist at the Food Science Research Insititute at the Auckland University of Technology.
He says the 15-month delay between the product being made and the presence of bacteria being publicly announced is because Fonterra may not have tested for it in the first place.
"And I think one of the issues is that we don't routinely test for clostridia in dairy products, except in cheeses, where they may cause 'blowing'."
He says it's possible a third party has used the whey protein in their own manufacturing, tested their finished product, found clostridia and asked what sort it was, which started the whole scare off.
"That probably explains why it's taken so long to show up, from May 2012 to March.
"Then of course it might have been at very, very low levels, so Fonterra would have had to go through their retention samples to find it - and that might have been very difficult if it is at low level."