LONDON (The Guardian) - For just two to three weeks of the year, forests across the northern hemisphere fill with a silent burst of activity as hundreds of litres of sap rise daily up through each mature birch tree in preparation for the spring.

Now companies are tapping into this, quite literally, to produce a drink hailed as the next so-called superfood, or "superdrink" - birch water.

There's nothing new about birch water. A traditional drink and medicinal ingredient in parts of Canada, China and Eastern Europe among others, birch water is birch sap that has been collected from birch trees as winter comes to an end.

To date, birch water production has been somewhat of a cottage industry, with producers harvesting sap for personal consumption or to sell to a domestic market. Now the growing industry is seeing brands emerge selling Eastern European and Scandinavian birch water to US and UK markets.

"Sourcing birch water is difficult," says Clara Vaisse, co-founder of UK birch water brand Sibberi. "There is no existing birch water industry per se, and thus no big supplier with existing procedures or an English-speaking commercial team. Birch water supply therefore has to come from multiple, local, small-scale harvests."

Unlike poorly-paid coconut farmers - harvesters of coconut water, the billion-dollar predecessor to birch water - the farmers Sibberi sources from are paid well for two reasons, says Vaisse: firstly, the trees occur within other forest types, such as oak and pine, so aren't necessarily easily accessed; secondly, the harvest only lasts once a year for a fortnight. This makes mechanising the collection process both impractical and unprofitable, so manual harvesting is paid at a premium.

Latvian birch water farmer Ervins Labanovskis, 35, is positive about the product's prospects: "We have been harvesting birch sap in my family for as long as I can remember, but only during the last four years has it also become my business. Currently I would say it creates 50 per cent of my income. But I am looking at this industry as a growing one and there is a high possibility that in a year from now it will be my primary or even only occupation."

Reflecting the nature of the birch harvest, Labanovskis' living situation fluctuates seasonally - during the winter he and his family live in Latvia's capital city, Riga, but in spring and summer they move to the more remote district of Smiltene. They harvest approximately 50,000 litres of birch sap per season, a portion of which goes to Sibberi, although he makes it clear that there is capacity to increase production to millions of litres per harvest if demand is there.

When asked what he thinks the advantages are of a growing birch water industry to the region, Labanovskis points to the additional employment it brings. He currently hires 15 people for two months of the year. These farmers generally have other principal occupations, such as grain cultivation or cattle breeding, but birch trees offer a good side business since the harvest is usually in April, "when winter works are finished and spring works have not yet started."

It is perhaps unsurprising that a raw material that's only available for two weeks of the year has its disadvantages. For a start, local partners such as Labanovskis have to be flexible - ready for a big, short-lived activity peak, although no-one is sure precisely when from year to year.

Likewise, companies must do accurate sales forecasts based on something only available for a fortnight, and in that two-week window harvesters must store a highly perishable product (birch water spoils in four days) to ensure it lasts until next harvest. To do so is expensive, difficult and costly if it goes wrong, not to mention environmentally demanding. Sibberi, for example, keeps its sap frozen at lower than -25C and then unfreezes it along the bottling process.

Mike Farrell, extension associate at the Department of Natural Resources, Cornell University, believes transportation is the number one issue when it comes to the environment: "The closer we can get production to consumption the better. If we develop a birch water industry in the US, for example, Americans could drink a more local resource, not coconut water from the Philippines." Sibberi is currently in conversation with landowners in Scotland to produce birch water for the 2016 harvest to sell to a UK market.

Farrell argues that a key challenge to the industry is simply getting people to understand what birch water is and to try it. He welcomes the 12 or so maple water companies that have sprung up over the last few years in the US, and believes it is only a matter of time before the same happens for birch water.

Importantly, he points out that scaling up would have no detrimental impacts on birch trees: "There is absolutely no shortage. If demand goes up, it's just a matter of sourcing new trees and tapping them. In the US alone, there are over one billion potentially tappable trees." Since companies such as Sibberi remove five or so litres of sap a day from the 300-400 litres that flow through each mature tree, tapping birches doesn't harm tree health as long as it is done properly.

While there is scope for the birch water industry to grow, and improve the sustainability of its supply chain in the process, British Dietetic Association spokesperson Elaine Allerton RD emphasises that the marketing messages around products such as birch water mustn't go unchallenged. "There is currently no evidence to support birch tree water as a 'superdrink'," says Allerton. "Indeed the term 'superdrink' or 'superfood' is a marketing term, not nutritional science terminology. It would be better to drink tap water for hydration, or milk if you want additional nutritional value as well as hydration."