The beer from the artisan producers - a 10% ABV Belgian-style ale - was brewed at Thornbridge, then re-fermented in Bourbon barrels with wild yeast lees produced from cider and perry fermentations for 18 months - but it was more than two years, and much work, in the making.
Garrett Oliver, Brooklyn Brewery’s brewmaster, said the idea for the brew came to him two years ago while producing the 'Ghost Bottle' series - experimental beers than are not commercially available.
He said: "We had used wild lees from natural wines to produce some of these beers, and I wanted to build on this by using lees from cider making. Thornbridge, as one of my best friends in brewing and one that is technically adept, were my obvious choice as a partner."
Rob Lovatt, head brewer at Thornbridge, said working with brewing legend Oliver was 'always an adventure'.
Lovatt said: "We wanted to break new ground with our barrel ageing. Not only in terms of scale, but also in terms of the challenges maturing and ?fermenting beer in barrels presents."
One of the big challenges Brooklyn and Thornbridge had to overcome was the choice of lees, which is the muddy sediment produced during fermentation of cider and contains numerous wild yeasts and bacteria.
Oliver said: "In November of 2013, we went to visit Tom Oliver, one of the world’s most respected and revered cider and perry makers, down in Herefordshire.
"After watching the maceration process and a tour of the fermentation rooms, where nature is allowed to do its thing and no sulphur is added to the tanks or barrels, we had an extended tasting and explained about the project. He was soon on board and agreed to send us all of his lees from the 2013 season."
Thornbridge then received polypins of wild lees from Oliver's, which is based in Herefordshire - each labelled with the specific fermentation from which it had come. During this time, the brewery also received a delivery of 120 fresh Bourbon casks, sourced by Brooklyn brewery directly from the Four Roses Bourbon distillery in Kentucky. Components of maturation and refermentation stages in place, Thornbridge then began to brew the base beer - a Belgian-style Golden Ale.
Lovatt said: "We were confident with the brewing and primary fermentation, but we were all aware that the maturation phase could go seriously wrong and with 120 barrels in total, that would be a big loss, so we needed to give real attention to detail to the entire process.
"The lees contained an unbelievable diversity of microflora that continued to metabolise the sugars still present in the base beer. Getting the temperature right and constant checks of every barrel was a top priority, to ensure the beer was in the right condition to let all the wild yeasts and bacteria to work their magic.
Lovell said that it had taken nearly 18 months of laboratory analysis and tastings to get to the 20,000 bottling stage.
Garrett Oliver flew from New York for the final blend and to assist with the bottling process, where a full bottling conditioning with Champagne yeast was put in place.
The last bottles - corked and caged - rolled off the production line after 3 weeks of solid blending and bottling, completing a project that had begun two years previously.
Oliver said he was delighted with the end product and how it illustrated fermantative "terrior".
He said: "Through natural lees, it is possible to take the fermentative “terroir” of a piece of countryside and concentrate it into a relatively small amount of liquid, and then have that terroir proliferate through a beer.
"It’s connecting beer back to the land. if someone didn’t tell you that Serpent was a beer, you might at first think that it was a cider, or perhaps an Arbois wine. The apple-like aromatics are apparent, along with a hint of oak, expansive fruit and a long bone-dry finish. It is a truly culinary drink and one that will pair very nicely with pork dishes, game meats and cheeses’.
Lovatt agreed and despite the 'sleepless nights' that he worried about the process, he was 'really captivated with it'. He said: "The final beer is completely unique, and seems to exist somewhere between cider, beer and wild ales such as American-style sours or lambic. We like to think the alliance between Brooklyn and Thornbridge has created something genuinely ground breaking, but most importantly, produced a great beer to drink."
Oliver summed up the worth of the Serpent collaboration saying 'this is about a beer that neither we nor Thornbridge could have made without each other."
Serpent, in 750ml bottles, is available from all good beer stockists - contact 01629 815 999 or email@example.com for further information.