Fonterra shares and units recovered somewhat after their initial extreme reaction but investors are still nervously awaiting further clarification of the extent of the contamination problem and how it occurred.
Three batches of whey protein concentrate used in infant formula have been found to be contaminated with the bacterium that can cause botulism.
The 38 tonnes of concentrate was produced at a Fonterra processing plant in Waikato in May 2012 but only made known at the weekend, prompting product recalls and import bans. Share prices fell sharply on the news, but have since recovered slightly.
On Monday evening, Fonterra shares - which only dairy farmers can own - rebounded from their opening $6.50 low to close at $6.92, but they are still below Friday's closing price of $7.14.
Fonterra units, which anybody can own, also recovered to close at $6.86, but they are still below the Friday close at $7.12.