When thinking of Switzerland many things may come to mind, but caviar-making sturgeon frolicking in hot Alpine springs is perhaps not one of them.

Yet, a tunnel project that unexpectedly uncovered hot springs in the Bernese Alps a decade ago is gradually turning the land of exquisite watches and sumptuous cheese and chocolate into a producer to reckon with of luxury caviar.

"We could produce the first Swiss caviar a year ago," Andreas Schmid, who heads marketing at Tropenhaus Frutigen, a company using geothermal energy from the Loetschberg rail tunnel to produce exotic fruit and now sturgeon meat and caviar.

Near the tiny village of Frutigen, in a valley flanked by towering, snow-dusted peaks, around 35,000 greyish black Siberian sturgeon bask in pools filled with naturally heated Alpine spring water.

This year, the company will produce up to 800 kilos (1,763 pounds) of caviar, selling on average at 3,000 Swiss francs ($3,232, 2,492 euros) a kilo, but it ultimately aims to have 60,000 sturgeon and an annual production of three tonnes of the black gold.

Standing in a production room, chilled to exactly four degrees Celsius (39.2 degrees Fahrenheit), Tropenhaus Frutigen's production manager Tobias Felix gently slits open the slimy, silver-white belly of a large sturgeon to reveal an abundance of tiny black eggs.

Another worker, who like Felix is wearing a hair net, face mask, white rubber boots and work clothes covered with protective blue plastic, steps forward and carefully sink his gloved hands into the fish to pull out several large handfuls of the pearly eggs, glimmering with silver under the florescent lights.

"From the time the sturgeon is killed, it takes about 10 minutes for the caviar to be salted" -- the last step in a process carried out entirely by hand, Felix explains.

Placing the precious eggs in a large metal bowl, he washes them with icy water before pouring them into a strainer and allowing them to drip dry for a few minutes.

Felix sprinkles on an exactly measured amount of Bex salt, mined in the Swiss canton of Vaud, and gently mixed it into the delicate eggs, before briefly lifting aside his blue face mask to taste the caviar.

Satisfied, he carefully distributes the caviar into dainty metal containers in different sizes, ranging from 30 up to 500 grammes, and labelled: "Pure Swiss Alpine Caviar".

The smallest tin, holding enough for a large mouthful of the slightly salty, bursting eggs, sells on site for 68 Swiss francs.

-- a complex tunnel project turns into caviar --

But how did caviar production come to this windswept mountainous land in the heart of Europe, far from the sea?

It is an unlikely story that begins a project to build an Alpine rail tunnel about a decade ago.

Engineers working on the Loetschberg tunnel were thrown when 18-degree Celsius water began pouring into the cavity at a rate of 70 litres (18.5 gallons) per second.

They were desperate to get rid of the water, but since it was so hot, it was impossible to divert it to the nearby river, where it would certainly harm the fish and plant life.

Chief tunnel engineer Peter Hufschmied, who was married to a Russian woman and well-versed in the joys of Russian caviar, came up with a surprising solution: to use the water to create a sturgeon farm.

Siberian Sturgeon, which when grown measure around a metre (3.2 feet) and can weigh up to 200 kilos (440 pounds), "very easily adapt to water temperatures and also like warm water," Schmid explained.

It was a lucrative business idea: the precious eggs make up a full 10 percent of the body weight of the large fish, which are relatively easy to farm even though they take years to reach maturity.

Raised in captivity, female sturgeon do not begin producing eggs until the age of six.

The first baby fish, purchased in France and Hungary, had arrived in Frutigen in 2005 -- two years before the Loetschberg tunnel opened, Schmid said, pointing out that Tropenhaus Frutigen had thus been able to produce the first Swiss caviar last year.

In 2011, the nearly 200 kilos of caviar was sold mainly on the domestic market, but Schid said the company was quickly broadening its focus and aimed to eventually sell two thirds of the black gold internationally.

But exporting sturgeon-based products is no simple matter.

Since the Siberian sturgeon have been over-fished in their natural habitat, the market is strictly regulated by CITES, a UN-linked organisation charged with protecting endangered species.

Permits are required to sell products based on farmed sturgeon, while CITES often puts in place moratoriums on wild sturgeon products due to lacking quota accords between the countries surrounding the Caspian Sea.

The sturgeon "is not endangered but it could be threatened if there are not strict controls," David Morgan, who heads CITES scientific team, told AFP.

Sturgeon farming, which has existed elsewhere in Europe since the 1970s, is a good thing since it "reduces pressure on the wild species," he said.

However, the practice could also have a flipside, he cautioned, pointing out that it could push down the value of the wild sturgeon and thus remove a major "incentive to keep the waters clean."