Courtesy of Bill Arnott at cask-centric Machine House in Seattle, here is a homebrew-scale recipe for their Dark Mild. This session-strength ale with rich malt character is ideal for cask-conditioning, but it should also hold up beautifully to kegging or bottling.
Batch size: 5 gallons (19 liters)
Brewhouse efficiency: 72%
5.5 lb (2.5 kg) Maris Otter
8 oz (227 g) chocolate malt
5.2 oz (147 g) crystal 60L
5.2 oz (147 g) crystal 150L
0.45 oz (13 g) Progress at 60 minutes [11 IBUs]
1.4 oz (40 g) Progress at 5 minutes [7 IBUs]
0.4 oz (11 g) First Gold at 5 minutes [2 IBUs]
Imperial A09 Pub or Wyeast 1968 London ESB
Mill the grains and mash at 152°F (67°C) for 60 minutes. Vorlauf until the runnings are clear, then run off into the kettle. Sparge and top up as necessary to get about 6 gallons (23 liters) of wort—or more, depending on your evaporation rate. Boil for 60 minutes, adding hops according to the schedule. Chill to 68°F (20°C), aerate well, and pitch the yeast. Ferment completely, allowing the temperature to free rise as high as 80°F (27°C). For 5 gallons (19 liters) of wort, prime with 2.4 oz (68 g) of dextrose and rack into cask or bottles. Condition warm or at cellar temperature for 14 days. Optionally, add isinglass before tapping and serving.
Clarity: Isinglass or other finings are optional in this case since this is a dark beer.
Priming: Instead of priming, you can rack into a cask when the beer is about 0.25–0.5°P from final gravity (i.e., at 1.009–1.010), but this really depends on the accuracy of your process. For homebrewing purposes, fermenting completely and priming is more reliable.
Carbonation: For cask, we are looking for 1.7–1.9 volumes of CO2, although for bottle conditioning we like to go a bit higher, to 2.0–2.2 volumes. Some breweries go a lot lower with cask (CAMRA—Campaign for Real Ale—recommends 1.1 volumes), although here in the United States, most other breweries seem to go way too high, in my experience. It’s really hard to pour through a beer engine any higher than 1.9, although venting allows some wiggle room. Carbonate to taste!