This style brings up bad memories for me. I had tasted several commercial versions of "Kentucky Common" before learning that they were all hopelessly, wildly inaccurate representations of the style. They were high in alcohol, dense with caramel, and sour as all get-out.
It wasn't until I started doing some research in preparation to brew my own that I realized these breweries were either woefully ignorant of history or trading on an impression of Kentucky alcohol as all being barrel-aged and/or sour-mashed. Neither of these impressions - common or not - is accurate.
Kentucky Common is a smooth, drinkable, light-amber beer with much more in common (no pun intended) with Kolsch and Cream Ale and California Common than with Jack Daniels. This style is ground-zero for me in the importance of knowing the history of beer rather than just inferring it from a lot of tasting in tap rooms and bars.
STYLE
The giveaway here that the strong, sour, or sweet versions of this beer are inaccurate would be the word "Common" in the name. "Common" ales, in almost all of their applications and appellations, refer to beers that are produced and sold in quantity to a broad audience, and that would militate against either a complex process or a costly grain bill.
Kentucky Common is an amber-to-copper and modest-strength (4-5.5 percent ABV) ale, with a simple grist comprising base malts and corn, with a touch of caramel flavor and a semi-dry finish. Bitterness is relatively low, with only about a 1:2 bittering-to-gravity ratio. And, perhaps most notably and importantly, this is an American style of beer. I don't mean in the "over-the-top hops and alcohol" sense, obviously.
I mean that this is one of just a few real, authentic, historically-American indigenous beer styles. As a result, domestic ingredients add a distinct and authentic flavor profile to the finished product.
RECIPE
A lot of recipes go whole-hog here and jump right back in to 6-row barley, but there's no need to go that authentic: 2-row has plenty of diastatic power to convert this sucker. Start with six pounds (2.7kg) of American 2-row and two pounds (0.9kg) of flaked maize. To this, we'll add a half-pound of chocolate rye (for color and some spicy drying in the finish) and a quarter-pound (0.11kg) of Crystal 40L. The overall flavor will be of grains-and-caramel, with a light body.
Some recipes call for simple sugar additions here, but I can't recommend it and we shouldn't need it, if fermented fully!
Hopping is simple: 20 IBUs of Cluster hops at a 20 minute addition will give you all the bittering you need and a classic rustic floral hops character lurking in the background of the beer. Cluster was (and, in some circles, still is) a workhorse hop of the American beer world until its splashier cousins started showing it up! Using it here is not only an homage to classic American brewing history, but also adds a perfect hops flavor for this style.
Finally, this is one of two beers (the other being Cal Common) where I'll sometimes use the Wyeast 2112 California Lager yeast, but there's a big "but" here. If you can't find it fresh, you're better off using either the 1007 German Ale yeast or any Kolsch/Cream Ale strain. A healthy pitch of yeast is more important here than the specific strain, since we want full attenuation at cooler temperatures.
PROCESS
First, if your water is soft-to-moderate in hardness, consider a very small (an eighth or quarter of a teaspoon) addition of gypsum in the mash. The light mineral character is historically accurate, and the flinty flavor is pretty pleasant. Aside from that, use your standard mash. You could go with a cereal mash if you're set up to do so, but I haven't found it to be necessary.
Lauter, sparge, and boil, then chill and aerate well before pitching. Sufficient oxygen is important here, because we want a dry beer with limited fermentation character, and reducing yeast stress is the best way to get both, and that means plenty of oxygen! Ferment cool, at an even 60F (16C), for about ten days, and then let the beer free-rise to anything above 68F (20C).
Cold crash, package, and carbonate to 2-2.5 volumes of CO2. I would recommend erring on the lower side of that range to help preserve a lighter mouthfeel, but even with more carbonation it should still feel very drinkable and light on the palate!
IN CLOSING
Historically, this beer, like many British pub ales, was delivered and consumed when it was fairly young, so don't feel like you need to let it sit around in your fridge to condition! It should drink well right out of the gate, given its simple flavor profile and cool, clean fermentation. Like many hybrids and lagers, though, it does age just fine, and in this case it will bring more of the malt flavors to the fore over time. The result could be a beer that isn't quite as snappy as the guidelines suggest, but the flavor is still quite enjoyable.
I'm happy to say that these days there are more and more breweries producing an "authentic" Kentucky Common, and I heartily recommend that you take a shot at this recipe and join them!