Dominion Salt site operations manager Euan McLeish talks through the harvest process at the Lake Grassmere saltworks.

They might get most of the attention, but grapes are not the only thing being harvested in Marlborough at the moment.

The piles of salt at the Lake Grassmere saltworks, visible to passing motorists on State Highway 1, are getting noticeably bigger.

Dominion Salt site operations manager Euan McLeish said the company was about three weeks into harvest, a process which lasted six to eight weeks.

1 of 6 SCOTT HAMMOND/FAIRFAX NZ Dominion Salt site operation manager Euan McLeish holds a chunk of salt from one of the 22 crystallising ponds at the Lake Grassmere saltworks. 2 of 6 SCOTT HAMMOND/FAIRFAX NZ The salt stacks. 3 of 6 SCOTT HAMMOND/FAIRFAX NZ Salt crust on Lake Grassmere. 4 of 6 SCOTT HAMMOND/FAIRFAX NZ The salt harvester loading trucks. 5 of 6 SCOTT HAMMOND/FAIRFAX NZ Salt falls from the gantry onto the stack 6 of 6 SCOTT HAMMOND/FAIRFAX NZ Harvesting pond.

The high sunshine hours and strong winds meant the yield from this harvest was on track to exceed the average of around 65,000 tonnes, he said.

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McLeish said it was no accident Marlborough was chosen as the site for a saltworks, as it had consistently high sunshine hours and little rainfall.

This helped the evaporation process, which concentrated the seawater as it passed through a series of ponds.

The 1416-hectare site had 46 ponds, including 22 crystallising ponds, which the concentrated sea water was put into last October.

These were kept topped up to a depth of around 350 millimetres, which allowed the sun to penetrate through the water, causing it to evaporate and leave a crust of salt crystals behind.

Harvest foreman Mike Tautari compared the process to farming, as it was entirely dependent on the weather.

"We're making salt while the sun shines," he said.

After the remaining brine was drained off the crystallising ponds, workers went through with a harvester, which scraped up the crust and deposited it onto a conveyor belt.

The harvester was capable of picking up 10 tonnes of salt a minute, and the 11 trucks that transported the salt to the two washing sites took around 300 tonnes an hour, McLeish said.

For harvest, the company brought in an extra 14 workers, to bolster the 45 permanent staff at the saltworks.

Tautari said it was common to do 11-hour days during harvest, as the company wanted the salt in before the weather turned bad and it got dissolved in the rain.

Once it had been washed in brine, the salt was stored in stacks, which could exceed 100,000 tonnes in weight.

Dominion Salt was jointly owned by Cerebos NZ and Australian company Cheetham Salt, which was in turn owned by Hong Kong company CK Lifesciences.

McLeish said the board of directors were committed to growing the Lake Grassmere site, pointing to the purchase of a new crusher for one of the two refineries and the development of new administration and office buildings.

The old buildings were wrecked by the 2013 Seddon earthquake, but McLeish said they would be replaced within the next 11 months.