Something fishy's going on.
The air is so thick it could be cut with pinking shears, wrapped up and taken home for the cat. It smells like someone's left the lid off the anchovy paste.
Goggled and masked, Pam Calvesbert is standing beside a big metal vat, stirring in mysterious dark substances.
It's not quite "eye of newt and toe of frog" and she's not wearing a pointy hat and cackling "double, double toil and trouble", but the brew is pretty potent, all the same. Just ask the farmers who spray it on their pastures.
Murchison dairy farmer Kerry Milligan says the fish meal fertiliser, called Vertefert, is one of the big reasons why his cows are in good health. "She's good stuff, all right," he drawls.
He no longer has to drench his cows for bloat. "It's good with the metabolic diseases like staggers and milk fever."
He says his grass is "nice and shiny" now and a recent herbage test shows it has metabolisable energy of 12.8 megajoules per kilogram of dry matter, which puts it in the high quality band.
Another farmer tells of conducting an unauthorised trial of Vertefert on the farm he was managing. He doesn't want to be named because it will identify the owners. He compared the fishy spray with urea and says that after a few weeks the difference was obvious.
The grass in the Vertefert side of the paddock was darker and thicker with lots more clover than the urea side. "I had to fence it off to stop the cows from lounging there all the day," he says.
But when he pointed out the results to the owners, they told him they would follow their consultant's advice and stick with a conventional fertiliser regime.
Mrs Calvesbert, who mixes up the brew in her Otaki factory, has an illustrated brag book filled with similar stories.
She says the addition of two natural growth promotants to the mix, triacontanol and giberellic acid, which change the grass cell structure, is responsible for the pasture being denser and for hay cut from it being heavier.
The brew's base is fish meal, to which are added 24 other ingredients. She won't name them all because she doesn't want her commercial rivals to steal her recipe, but they are all from natural sources.
However, even if someone did discover her formula she says they would have difficulty in re- creating the product because the trick to its success is in the timing of each part's addition to the cooking pot.
Her experience as a brewer goes back to the mid-70s in South Auckland when she began making a blood and bone-based mix to a recipe developed by an octogenarian Sydney veterinarian, Peter Kauzal, with the aim of improving livestock health.
With Mr Kauzal's help, she adjusted the blend for New Zealand conditions and put it on the market. The first buyer was an orchid society and other home gardeners and horticulture growers began to use it.
Farmers also became interested. "It was the older guys who remembered what their parents did before the war," she says. "They were seeing too much metabolic sickness in their herds and were looking for an answer."
The business grew and was sold in 1987. She signed a five-year restraint of trade and it wasn't till 1993 that she re-entered the market, this time based in Porirua.
By then, blood and bone brews had been banned on farms producing for export after animal disease scares in Britain, and she turned to fish meal as a substitute. She still makes Synerlogic, a blood and bone-based fertiliser, for home gardeners and horticulture.
She and husband Ray set up under the name Blooming Good, opened a shop and worked side by side making brews in the factory.
Mr Calvesbert, a plumber, brought practical skills to the business and although illness is keeping him from the factory now, she describes it as a team effort. "I couldn't have done it without him."
Starting again was hard work, she remembers. "You're a lady from a little tin shed factory and you've got to convince these farmers that you know what you're talking about. They look at you sideways."
However, some who were looking for alternatives to superphosphate and urea gave her brews a trial. She works through distributors as well as taking orders at show and field days and through a webpage.
'I T'S not a magic bullet, it can't fix everything," she says.
For many of the farmers, the benefits don't become apparent immediately. "Their accountant will say: 'You haven't spent much on the vet this year, are there some bills you've forgotten to put through?' And the farmer thinks: 'Maybe it's the fish fertiliser I have to thank for this'."
Applying the brews by spray is best, she says, and refers to research at Michigan State University in 1953 that found foliar feeding to be 60 per cent to 90 per cent more effective than conventional soil fertilisation.
It means that her fertiliser, which is diluted and applied in small quantities, is not wasted. She says the smell, which is so strong in the factory that she and her two workers have to be closeted in a special room and wear breathing masks and goggles while making it, becomes "vaguely beachy" on the pastures.
The fish meal has high nutritional value. It is 63 per cent protein, contains phosphate and is high in amino acids, nature's building blocks.
The other ingredients include natural sources of the growth promotants and of minerals and carbohydrates and blend together under her expert eye. This is her point of difference with other fish- based fertilisers.
She claims Vertefert's NPK rating of 8-3-6, along with the other elements and natural ingredients enrich the soil and combine with the soil's biology to improve plant growth. Pastures have improved mineral content, dry matter per hectare, metabolisable energy and clover, less litter and better resistance to pests.
Dairy farmers tell her they are producing more milk on Vertefert, with one saying he has lifted his pasture production by 26 per cent in five years and now does not use urea. Sheep and beef farmers say they see less erosion on hills because of deeper rooting pastures.
The business moved to Otaki in 2003 and last year, with her husband ill and with a sore elbow from stirring and mixing, she decided, at 62, to put it on the market.
She phoned her South Island distributor, John Barnes, the owner of his own business, Fertiliser New Zealand, and was told: "You can't sell, it's mine." They came to a "very amicable arrangement" and ownership changed hands.
Part of the business's value was her intellectual property - the knowledge of the brews' formulas and the blending skills - and she has stayed on to train new staff.
It has given her time to plan a new product, a time-sensitive compost "tea" that can be made fresh weekly for regular customers.
She has seen attitudes to her change over the years, from being regarded as part of the "hippie dippy flower power" generation to being almost trendy.
"It's been a bit of a battle," she says. "But I'm proud to have got through without getting into debt I couldn't get out of."
The trendiness is coming from fears of global warming. "It's made the country pull its socks up and make sure we live up to our clean and green image. Part of that involves taking a closer look at the fertiliser industry. That's where we come in. People can now fit us into a slot they couldn't fit us into before."
In the meantime, it's business as usual at the factory. She has got used to the smell and it is true that after a couple of hours the senses become deadened to it. Which can be a trap.
She usually goes home and changes before going out again. But one day she called in at the supermarket on her way home.
Standing at the checkout she realised the operator was sniffing the air. "Oh, no," she said. "I've got to run after that gentleman who just left. One of those mussels he bought must be off."
"I had to tell her that it wasn't the mussels, it was me," Mrs Calvesbert says. "I can smile about it now, but it was a bit embarrassing at the time."