Corny Keg vs Commercial Keg

Why homebrewers use cornies

Three reasons, none of them capacity

The lid comes off. This is the decisive one. A corny keg has an oval pry-out lid large enough to get a hand and a cloth inside, which means you can actually clean and inspect the vessel. A sanke keg is a sealed stainless shell with a single valve, and cleaning one requires a pumped CIP setup that forces cleaner through the valve. For a homebrewer, a vessel you cannot open is a vessel you cannot trust.

It matches the batch. A 5 gallon corny takes a 5 gallon batch, which is what the overwhelming majority of homebrew recipes are written for. A half barrel would need three batches to fill, and a part-full keg of beer under gas is beer you are slowly losing.

Four fit a kegerator. At roughly 8.5 inches in diameter, four cornies occupy about the footprint of one half barrel. That is why kegerators are rated as “one half barrel or four cornies” -- and why four different beers on tap is a realistic home setup.

Fittings

Ball lock and pin lock are not interchangeable

Corny kegs come in two incompatible connection standards, a legacy of the soft drink industry they came from.

• Ball lock. The homebrew default. Disconnects push on and lock with a sliding collar. Gas and liquid posts are different sizes so you cannot cross them. Nearly every kit sold is ball lock.
• Pin lock. Disconnects twist onto pins. Gas posts have two pins, liquid posts three. Pin lock kegs turn up cheaply secondhand, and they are perfectly good -- they just need pin lock disconnects, and the kegs are slightly shorter and wider than ball lock ones.

Pick one standard and stay with it. Mixing means two sets of disconnects and a recurring source of confusion in a cold cabinet.

Buying used

Reconditioned cornies and what to replace

Reconditioned corny kegs are excellent value, because they come out of commercial soft drink service in large numbers. What they also come with is old rubber, and every seal is a potential slow leak that quietly empties your CO2 cylinder.

Replace the whole set before first use: the lid gasket, both post O-rings, and both dip tube O-rings. A complete seal kit is inexpensive and fitting one prevents a frustrating week of leak-hunting. Then pressurize the keg, spray every joint with soapy water, and look for bubbles before you trust it with beer.

Part numbers, dimensions and dip tube variants are all in corny keg sizes and parts. If you want to ferment in one rather than just serve from it, see fermenting in a keg.