It is smaller but almost identical in design to one at Fonterra Darfield, said to be the world's largest milk powder dryer when it began operating in 2013.
The Pahiatua site processes milk from 500 farms, from northern Hawke's Bay to southern Wairarapa. Its Tararua District is a big milk producer.
Milk from Fonterra's Rangitikei, Wanganui and South Taranaki suppliers goes to Fonterra Whareroa, near Hawera.
Fonterra is New Zealand's biggest milk processor, with more than 30 sites in New Zealand, and 25 overseas.
The Pahiatua site makes only whole milk powder.
Its increased capacity would allow milk to be diverted to it, allowing other plants to specialise in ultra heat-treated milk for Fonterra Waitoa UHT, in Waikato, or mozzarella cheese for Fonterra Clandeboye, near Timaru.
Fonterra is committed to sustainability, Mr Spurway said.
The new dryer reuses excess heat from boiling milk. And it treats and reuses water, then puts it through a treatment plant before discharging it to irrigate land on four farms.
"That allowed us to increase site throughput without increasing water take, and we have also improved the quality of our wastewater."
Hygiene is important. Reporters crossing the "red line" into the new dryer had to remove watches and jewellery, and leave their shoes behind. They got into overalls that covered their clothes, wore safety glasses, white gumboots and hairnets and carried earplugs to block out noise.
There was a huge amount of hand washing and hand sanitising before entry - at least six times in all.
"We don't want any foreign matter getting into any product," Mr Spurway said.
The new dryer goes day and night and needs shifts of eight people to run it.
It created 45 new jobs, and brought the number employed at the Pahiatua plant up to 175. Milk that comes into the dryer is first "standardised", so that it has the required content of constituents such as fat, lactose and protein.
After that it is boiled to increase its solid content from 13 per cent to 50 per cent, giving it the consistency of condensed milk. It is boiled in a vacuum, which means boiling can occur at 55 to 65C, rather than the usual 100C. The resulting steam is used to heat other parts of the process and the resulting water is treated to drinkable standard.
The new plant has three evaporators, with two working at once to allow the third to be cleaned.
After that the viscous milk solution goes into the 25m-high drying chamber, where air more than 200C is squirted at it at high pressure. Further drying is done in a vibrating fluid bed.
After that, sack after 25kg sack is filled every few seconds, as regularly as a ticking clock, in an automated packing sequence.
The batches are all marked, so the milk powder can be tracked if there is a problem.
It is sold in the Global Dairy Trade auction and goes to 20 countries. Fonterra's predicted payout for a kilo of milk solids this year is $3.85.
Milk production is expected to be 2 to 3 per cent down this season, as farmers respond to the lower price by dropping costs and productivity.
Mr Spurway expects things to improve.
"Prices have lifted in the last two Global Dairy Trade auctions. The stores are fairly empty. We've reduced the amount we are selling on the Global Dairy Trade auction.
"We're selling milk through other channels, finding demand and selling at the most valuable channels."
