After being washed and dried, the potatoes are bagged depending on the size the buyer wants.
The small gourmet-sized ones are at the high-end of the product range and bring the best return, as they snapped up by restaurants.
Frew said it took plenty to make a tonne of them but they were now fetching about $1800 a tonne.
He has experimented with different seed and reckons nadine is the best - they retain the best skin after washing and don't bruise as do some other types.
Starting with a farm of about 30ha, Frew and his family have gradually bought more farmland to the point where they now have a total of 25 properties covering 3235ha between Raetihi and Waiouru to the south of Mt Ruapehu.
It's a family affair. Frew has his two sons, Peter and Ronald, involved. Ronald manages one of the farms but also farms on his own account. Daughter Jenny looks after IT, wages and other administrative duties, and Frew's wife, Peggy, handles day-to-day administration.
They employ 16 permanent staff and bring in casual workers when production demands.
There are growers who produce more than the 6000 tonnes the Frew Partnership harvests each year, but this family enterprise is one of the country's largest producers of specialist spuds.
The sheep and beef operation is also on the large scale and they run 20,000 ewes and 1000 head of beef.
The nature of growing potatoes has seen growers in the Waimarino accumulate considerable tracts of land.
They can't grow the tubers in the same ground every year so rotating the crop means they have to find new paddocks. "To get our 250 acres (100ha) of suitable ground every year has become increasing difficult, but if you're looking for fresh ground every year you have to buy more land."
Potatoes are planted in one area every five years and it's this cycle that pushes the demand for fresh paddocks.
The biggest domestic customer for the Frew family is the Foodstuffs group of supermarkets.
"They prefer a bigger, washed potato and we've been supplying them for the past 20 or so years," says Frew. "We're obviously meeting their expectations because we haven't had a rejection for years, so that's good."
When Frew started growing potatoes in the 1960s it was considered a fool's errand but despite that, he started pushing the growing boundary.
"I started growing seed potatoes at Waiouru and found I could actually grow table potatoes up there. The cold is marvellous for them."
By 1987 potato-growing had all but faded out in the Waimarino and Frew was the only grower left. That year he planted 20ha of potatoes in one paddock and sold the first crop at $6 for a 20kg bag in April. By November he was delivering them to Auckland and getting just $1.50. Then the nadine seed arrived on the scene, which proved to be the turning point. "The nadine handled the washing and had a brilliant skin finish so we got into washing the crop."
Planting starts in September with the bulk going into the ground in October and November and the last seed planted in December.
The last plantings will stay in the ground to be harvested the following October. They can do that because the cold weather and friable volcanic soils act as a natural coolstore.
"That's a big plus for this area. Because the soil is so free-draining you can use it as a storehouse and the crop comes out in remarkably good condition."
At 70 years old, Frew has no intention of putting his feet up and the partnership's latest acquisition - a dairy farm north of Raetihi - is testimony to that.
He reckons that within three years they will be milking at least 900 cows once a day.
But as well as milking cows, the flat land means another 28ha can be used to grow potatoes every year.
