If you follow Moody Brews on facebook, twitter, or instagram, you may have noticed that (a) I am brewing at Vino’s Brewpub again and (b) we have been referencing “cask conditioning” again a lot more frequently. If you have ever wondered what cask conditioning exactly means, this blog post aims to explain the age old process by documenting my preparation of a few cask kegs in December 2015. One of the best aspects of making beer at Vino’s (where I started professionally) is they have a nice fleet of fairly unique stainless steel cask kegs. These are typical beer kegs, American sanke, spear, with the exception of one thing: a hole (bung) in the center of the keg. More on that later.
During normal fermentation activities, yeast are metabolizing sugar in the wort to produce ethanol and carbon dioxide. We as brewers shepherd this process along during cellaring by controlling initial concentrations of oxygen (for yeast health) and fermentation temperature (which directs yeast metabolic processes away from developing what we consider “off flavors” in the beer). When the yeast finish eating sugars, we then filter and rack (transfer) beer over to a “brite” (conditioning) tank, where we artificially carbonate the beer.
We didn’t always have this nice, steady supply of bulk carbon dioxide delivered to our door, where we can exactly achieve the carbonation desired in beer. That’s where the cask came in. Initially in a wooden barrel, finished, unfiltered, uncarbonated beer was dosed with a touch of priming sugar in the barrel, filled, then sealed. The barrel, or cask, was allowed to sit in ambient temperatures for a few weeks wherein yeast would ferment the added sugar, producing a touch more ethanol and just the right amount (theoretically) of carbon dioxide with no place to go but dissolve in the beer, pressuring the cask to just the right amount of carbonation for a “proper pint.” If you have ever helped bottle home brewed beer, this is exactly the same process.
The practice of cask conditioning beer is not an exact science. Different yeast strains have different degrees of attenuation, that is, ferment more of the sugars in the wort than other strains. Some yeast strains, particularly Belgian strains, take a hiatus during fermentation for months, then, almost inexplicably take back up the process. These factors, coupled with the amount of priming sugar used can make the difference between a flat beer and, in essence, a bomb. Once you seal the cask (by the gratifying act of hammering in a wooden bung), you have this product inside the cask, living, developing, maturing that you cannot shepherd any longer. The brewer has to wait, hoping he added the right amount of sugar, hoping he calculated attenuation properly, until, after a few months, he can tap the keg and see how the beer developed. For me, it’s a nod to tradition.
Yet also, this is when I get to experiment. I love working with my local community garden, Dunbar Community Garden Project, and I have used everything from scorpion peppers (in a milk stout), hops (in a cream ale), lavender (in a maibock), and pluots (in a saison)–all grown at Dunbar, about six blocks from the brewery. Using these kegs is incredibly useful because it allows me to experiment with some pretty crazy beer one keg at a time, and there is many times, limited product where I don’t have enough to add to an entire batch of beer. Some of my best beer have come out of these cask kegs, and it is a treat to get to play with them at Vino’s again.
Yesterday, I made a few cask kegs with a black Kölsch-style ale I brewed a few weeks ago. Here’s my process:
Before we fill, we prep. I decided to do a citrus treatment to this black ale that is surprisingly light bodied, only slightly chocolate-y, and an easy drinking 5.1% ABV. In one cask, I planned on adding lime zest and Equinox hops (known for a lemon lime hop aroma); in the other, grapefruit zest and Pacifica hops from New Zealand (orange and grapefruit aroma). I added the zest only because the pith (white portion) of the fruit can lend an unpleasant bitterness I wanted to avoid.
Once zesting is complete, I added a touch of honey to a previously cleaned and sanitized cask keg. The honey provides sugars the yeast present in the unfiltered beer with ferment and carbonate in the keg. Next I affixed a sanitized cloth sack to the inner portion of the bung and filled the sack with respective zest/hop combination.
And then, the stress-relieving, deeply gratifying step of hammering the wooden bung into the hole of the keg. No small amount of force is required, as the inner pressure during the keg conditioning process can reach upwards of 26 PSI at room temperature. The bung has to stay in place to keep the seal.
Finally, we wait. While we go on with our normal brewing activities, we will put these cask kegs on tap a few months down the road, and, like unwrapping a present, see what unfolds! I hope this has helped explain the labor intensive process of cask conditioning. Cheers and hope to see you for a pint of something special at Vino’s!