Fonterra's handling of the whey contamination incident will be put under the spotlight in a full internal and external review.
The company's head of New Zealand milk products, Gary Romano, said on Tuesday the review would include an investigation of the time it took to identify possible botulism contamination in three batches of whey protein manufactured in July last year, and then inform the authorities and the public.
Mr Romano side-stepped questions about the time frame, but confirmed that the first indications of possible contamination came from routine testing in Australia in March, when a broad test showed elevated levels of some organisms.
"That certainly made us curious as to why this was, and we did do some further testing from that time," he said.
It took further specialised tests not usually done on dairy products to reveal the botulism connection, which Mr Romano said was rare in dairy products.
"Worldwide, I think since 1950, we can see maybe 10 cases where there are some links to dairy.
"It's one of the reasons we were very surprised with the result. What we needed to do was to go back and understand what has actually happened to cause it."
All but a small amount of the products containing the suspect whey protein had now been traced, Mr Romano said.
