The unusual taste that prompted a recall of some Anchor blue top milk is due to cows eating turnips or swedes, Fonterra says.
The dairy company pulled the milk off shop shelves in the lower North Island after receiving complaints from customers about an unpleasant taste.
The company said an investigation found the cause was most likely brassicas, like turnips or swedes, fed to cows when grass was scarce.
It said testing of the unusual-tasting milk before it was distributed didn't pick up the change.
Fonterra Brands New Zealand managing director Leon Clement says it was clearly a feed issue.
Mr Clement said while the milk was safe to drink, a few batches with Best Before dates 22-27 were being removed from shelves.
Fonterra said customers concerned about the quality of their purchase should return it to the shop they bought it from, or contact the Fonterra Customer Care team on 0800262467.