Liquid gold: Overseas experts have long said maple syrup couldn't be made in NZ because the weather is too mild. Not true, say Canterbury academics.

Canada produces 71 per cent of world's maple syrup and 91 per cent of that originates from the province of Quebec. But a clutch of New Zealand academics think this country could have a maple syrup industry, despite a mild climate and no sugar maple forests.

Their preliminary research has "determined that a plantation of maple saplings for use in commercial production of maple syrup is a possible and a promising endeavour in New Zealand", according to a presentation to be given at a chemical engineering conference in Queenstown on October 1.

The most promising places for maple syrup production are roughly Molesworth Station and inland from Westport, both in the South Island, according to their paper.

But we're a long way from pouring kiwi maple mīere​ over our pancakes because the research challenges many accepted truisms of maple syrup production.

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In North America, maple syrup is derived from the sap of maple trees (Acer saccharum). The sap is mostly colourless water, with 1 per cent to 3 per cent sugar by weight. Holes are drilled into mature maple trees and natural pressures within the trees flow the sap into tubes for collection.

The sap is then reduced by heat until the sugar content is about 67.5 per cent by weight. It takes about 40 litres of sap to produce 1 litre of syrup. The amber colour comes from the heat.

In Quebec and other syrup regions of eastern Canada and the US, maple trees are 30-40 years old before they are tapped. These trees typically occur in natural forests.

Finally, maple trees are unusual in that sap flows in winter. Why is not well understood, but a freeze-thaw cycle is critical. Winters in Quebec are harsh and overnight temperatures are consistently about minus 10 degrees Celsius. But there are thaws too.

Overseas experts have long thought maple sap production could never occur in New Zealand because the weather is too mild, wrote lead author Tenaya Driller, a chemical engineering PhD student at the University of Canterbury.

But in 1984, Dave DeGray​ started planting sugar maples near Nelson and his tree growth rates are almost double those achieved in North America, reaching tappable girth in 20 years. He harvests some sap.

Luce Morin, 123rf Maple sap is often collected through tubes in industrial operations in North America.

Driller and her engineering supervisor, Dr Matt Watson, aren't interested in 20 year cycles. They adopted a "plantation method" that was developed at a maple research centre at the University of Vermont.

The key feature is that sap can be extracted from maple trees that are a few years old and a few centimetres in diameter at breast height.

The top of the saplings are cut off and a "sap collection device" draws out the sap using a partial vacuum. Topping the saplings does not kill them.

While less sap comes out of each sapling than comes out of each mature tree, the density of a plantation makes up the difference.

In a plantation, saplings would be 30cm to 100cm apart and there could be 12,000 saplings a hectare. Natural forests average 250 trees a hectare.

Meanwhile moderately cold temperatures can penetrate thin saplings and encourage sap production. It takes more sustained and lower cold temperatures to penetrate a mature tree.

Driller, Watson and groups of undergraduates crunched the numbers and concluded the payback period was seven years for a 10ha plantation of maple saplings, a vacuum harvesting system, plus processing and packaging systems.

Finally, the researchers identified the most likely regions for a maple plantation and found Molesworth Station and inland Westport looked the most promising. These were "coarse" calculations, Watson said.