A $212 million project to add a fourth milk drier to the plant is scheduled to be finished on September 1 and will leave the plant capable of processing 15 million litres of milk a day.
Project manager Dean Shilvock said the new drier could produce 27 tonnes of milk powder an hour, or 150,000 tonnes a season, and would work alongside three smaller driers at the site, one handling seven tonnes an hour and two 14 tonnes an hour.
Next season, the new drier was expected to process 620 million litres of milk into regular UHT and instant whole milk powder.
Mr Shilvock said Edendale's extra capacity was needed to handle projected milk growth in the South Island by 2012-13, but in the meantime it would process surplus milk from the company's Clandeboye plant near Timaru.
It also took milk from Clandeboye last season.
Between 400 and 450 contractors from throughout New Zealand have been building the new drier, as well as a new boiler, a 120m by 60m new dry store and upgrading the wastewater system.
Mr Shilvock said the first drier was built at Edendale in 1994, the second in 2002 and the third in 2003.
Casein plants were built in 1996 and 1998.
When the fourth drier was completed, an extra 30 to 40 people would be employed, taking the site workforce, including tanker drivers, to about 390.