It’s been a long time since Heineken released a new beer so we knew that when their secret lager project was going to drop, it was going to be massive—but we didn’t see this coming.

After three years of experiments, Heineken have finally released H41. In a first for Europe, and indeed the whole world outside of Argentina, H41 is brewed from a wild yeast found only in remote parts of Patagonia.

Known as the ‘mother yeast’, this rare and delicate creature is what gave birth to Heineken’s ‘A-Yeast’—the yeast they’ve used as a brewery for 130 years. Yeast is what kicks off the fermentation process, making the beer alcoholic. It has its own flavor, but as a living organism, it also has its own behavior.

Like taming a wild animal, using the rare yeast hasn’t been easy.  “There's only been a couple of times in the history of brewing that a yeast from the wild has been brought into a brewery." says Willem van Waesberghe, master brewer at Heineken. "When we started working with it, it just died on the spot; our fermentation conditions were not good enough. In fermentation, you put the yeast in a happy environment where it starts producing alcohol, which means the yeast is cloning itself, it’s growing.

“When yeast grows it produces alcohol. You need to get the circumstances right - the temperature, the pressure. It took us years to get a process constructed around the yeast, and now finally we can launch it. I mean I think we're not even ready yet completely, but it’s good enough.”

Willem discovered the 'mother yeast' in a scientific article nearly four years ago. Heineken now hold the exclusive license for use of this yeast worldwide, outside of Argentina’s own microbreweries. The project – which forms the first chapter of Heineken’s ‘Lager Explorations’, a series of experiments with lager – has even funded a new yeast research centre in Argentina.

But the key question: does it taste good? We taste tested a few sneak peek bottles in the Complex UK office and the answer is hell yes.

“The taste is really the one which blew us away” says Willem. “The spicy note which comes out next to the fruit…a normal Heineken has this fruity note but by changing the yeast we make this very spicy flavour, a little bit clove like.”

And as a yeast that only grows at temperatures under 15 degrees, you know it’s going to hit the spot chilled on a hot summer’s day.

“It is the dream of every brewer that you can bring in a yeast from the wild and create a new lager style. Lager really is full of surprises.”