Specialty coffee has become a hotly contested industry, where farmers, roasters and cafés are always trying new things to find their competitive edge. We’ve seen a lot of interesting processing methods in the last few years, with funny names like anaerobic natural, carbonic maceration, or lactic fermentation.
Something different that some producers have been playing with is barrel-aging their coffee. The idea seems straightforward, but there are actually quite a few things to consider.
Second-hand oak barrels that have been used to age whisky, rum or wine are used for this process, as the alcohol leaves a boozy aroma in the barrels. They are then filled with green coffee for anything from a few weeks to several months, letting it mature in the rich, aromatic environment, imbuing it with rich, woody, heady, chocolatey flavours.
This is done before roasting because green coffee beans are extremely porous. They are like little sponges, soaking up all the aromas in their surrounding environment. This is normally a headache for farmers and roasters, who take great care to store their green coffee in a clean space, using hessian sacks lined with plastic to keep the beans extra protected. But barrel-aging exploits this absorbent tendency, letting the coffee soak up the oaky, boozy goodness in the barrels.
This is what whisky brewers would call “additive” barrel-aging, as the flavours from the barrel are being added to the whisky (or in our case, coffee). But there are two other types: “subtractive” and “transformative”. Whisky barrels are normally burnt or charred on the inside, leaving them lined with active charcoal – the sort of thing you’d find in a water filter. This can be used to remove or “subtract” certain unpleasant flavours, cleaning up whatever it is you’re aging. Finally, substances from the barrel can team up with substances in the coffee to create new compounds and therefore new flavours, “transforming” the coffee beyond just absorbing the aromas of the barrel.
Another layer can be added by considering the processing method. Barrel aging is particularly suited to naturally processed coffees, which already have undergone a fermentation stage. This generally gives a funkier, more potent coffee, often with similar boozy notes. Resting it in a bourbon barrel, for example, would turn that note up to eleven.