At Goose Island, we use oak barrels in two distinct ways
We use bourbon barrels to extract the distinct character of the spirit and the barrel into a couple of our very special beer releases each year. Bourbon barrels are made of 100% newly constructed charred American White Oak. The staves are formed from planks of oak that are open air cured before coming together to form a barrel held together by large steel rings. The inside of the barrel is charred, caramelizing the wood sugars and securing the shape of the barrel.
The brewers at Goose Island use 100% malt for Bourbon County Stout. Six different malts weighing a total of nearly 5,000 lbs are used in every brewhouse turn.
Bourbon County Stout will see a boil lasting 3-4 hours to condense sugars by boiling off approximately 30% of the water. Hops are added to every turn of Bourbon County Stout to balance the sweetness of the malt.
Chilled wort is pumped into a fermentation tank. Fermentation begins after the first couple of turns are in the tank, and then there are four more coming after that. With all that available sugar the yeast starts a rapid, rowdy fermentation.
Post fermentation the base Imperial Stout is a bit rough around the edges. It is pumped into freshly emptied bourbon barrels to age for 8-12 months in the non-climate controlled Goose Island Barrel House on Chicago's West Side.
Chicago has hot summers, cold winters, with pleasant springs and autumns from the climate moderation from the large Lake Michigan body of water. During hot Chicago summers the warm temperatures cause the wood to expand. Expansion allows the beer to penetrate deep into the wood pores and come into contact with the bourbon layer of the barrel staves. Cold temperatures cause the wood to contract. Contraction squeezes the beer out of the wood pores and back into the contents of the barrel, bringing with it the character of the bourbon that was trapped in the bourbon layer.
The changing of the seasons with the expansion and contraction of the wood pulling and pushing beer in and out of the wood will result in the beer picking up characters of each layer of the barrel.
The porous nature of the wood allows small consistent amounts of oxygen to come into contact with the beer. Wood allows liquid to evaporate from the barrel, making the beer more concentrated, resulting in a richer flavor. The term "Angel's Share" is used to describe the lost volume due to evaporation during the aging process. There is loss of volume due to absorption into the barrel as well which is referred to as "Devil's Cut".
After the 8-12 months of the Imperial Stout aging in the bourbon barrels, the process of blending each barrel together begins. Each year our weather in Chicago is a little different and each year brings a unique complex profile of bourbon, chocolate, coffee, dark fruit, vanilla, caramel and wood to our Bourbon County Brand Stout.