Fonterra's Edendale site operations manager Keith Mason said the new dryer, the fourth on the site and known as ED4, can process 100 litres of milk into 10kg of whole milk powder in just over one second.
Its capacity was 30 tonnes an hour and during the dairy season it will produce about 135,000 tonnes of powder.
Mr Mason said commissioning and testing the $212 million plant took several weeks to complete.
He expected Fonterra to take ownership from contractors from October 8.
After that, it would be at full production.
He said commissioning had gone well and product from the dryer was of export quality, which was testimony to its design and construction.
An estimated 800,000 cows from 800 farms in Otago and Southland will supply the Edendale factory this season, with the milk from an estimated 160,000 of those cows going to ED4.
Mr Mason said the site could now handle 15.1 million litres of milk a day.
ED4 was capable of handling 4.4 million litres a day.
The new dryer, creating an extra 31 jobs, would work alongside three existing dryers, one producing seven tonnes an hour and two at 14 tonnes an hour.
