If you've spent any time in the homebrewing world, you've heard of Cornelius kegs — usually called corny kegs or just cornys. They're the workhorse of small-batch beer dispensing, and the used market for them is one of the most active corners of the keg world.
Here's everything you need to know before buying or selling one.
What is a Cornelius keg?
A Cornelius keg is a stainless steel pressure vessel originally designed to hold and dispense soft drink syrup. They were manufactured starting in the mid-20th century by the Cornelius Company (now part of Marmon/IMI) and used by bottlers and restaurants for decades.
When the soda industry transitioned to disposable bag-in-box syrup containers in the late 1980s and 1990s, millions of these stainless tanks suddenly became surplus. Homebrewers — who needed a small, refillable, pressurizable container for finished beer — adopted them en masse. The corny keg became the de facto standard for homebrew dispensing, and the secondary market has thrived ever since.
Ball lock vs pin lock: the soda wars legacy
When you shop for corny kegs, the first decision you'll face is ball lock or pin lock. The reason is straightforward: Pepsi and Coca-Cola used different connector standards, and both designs flooded the homebrew market.
Ball lock kegs were used by Pepsi. They have smooth, round posts on top, and the connectors lock on with internal ball bearings. They tend to be slightly taller and narrower than pin lock kegs.
Pin lock kegs were used by Coca-Cola. The posts have small metal pins protruding from the sides, and connectors twist on and lock against those pins. Pin lock kegs are typically shorter and wider.
Both work equally well. The connectors are not interchangeable, so once you choose a style, all your future kegs, disconnects, and accessories need to match. Ball lock is more common in the U.S. homebrew market, which usually makes parts easier to find. For more on connector types across all keg styles, see our guide to keg valve and fitting types.
Common sizes
Cornelius kegs come in three main sizes:
- 5 gallon (19 L) — The classic and most common size. Holds roughly a standard 5-gallon homebrew batch with headspace. This is what most homebrewers buy first.
- 3 gallon (11.4 L) — A smaller, more portable option. Useful for split batches, sour beers, or anything you want to dedicate a keg to without committing 5 gallons.
- 2.5 gallon (9.5 L) — Less common but available. Same fittings, just less volume.
Dimensions vary slightly by manufacturer, but most 5-gallon corny kegs are around 25 inches tall and 8.5 inches in diameter — small enough to fit four in a typical kegerator.
Why corny kegs dominate homebrewing
A few practical reasons:
- Refillable and reusable. Open the lid, fill with beer, seal, pressurize, dispense.
- Easy to clean. The lid comes off completely, so you can reach the interior with a brush or PBW soak. Sankey kegs, by contrast, require special spear tools to fully clean.
- Right size for homebrew batches. A 5-gallon batch fits perfectly.
- Pressure-rated. They're built to hold carbonated soda at force-carbonation pressures, so they handle beer carbonation easily.
- Stackable. They're built to stack two-high in commercial use.
Buying used: what to inspect
Most corny kegs on the market are 30+ years old at this point. They were built well, but they're not immortal. When inspecting a used corny keg, check:
- The lid gasket. O-rings dry out, crack, and harden. Plan to replace it.
- The post O-rings. Both gas-in and liquid-out posts have small O-rings that fail. Cheap to replace; replace them on every used keg you buy.
- The dip tubes. The liquid-out dip tube reaches near the bottom. The gas-in is short. Check both are present and undamaged.
- The poppets. Small spring-loaded valves inside each post. If they're stuck, leaking, or missing, the keg won't seal under pressure.
- The interior. Look for pitting, rust, or stubborn syrup residue. Stainless doesn't rust under normal conditions, but exterior surface rust from sitting wet is possible.
- The pressure relief valve (PRV). Usually a small ring you can pull to release pressure. Make sure it actuates freely and reseats.
- Dents. Cosmetic dents are fine. Dents around the post weldments are a problem.
For a general inspection framework that applies to all keg types, see our used keg inspection guide.
Replacement parts you'll likely need
The good news: corny keg parts are inexpensive and universal within their style (ball lock or pin lock). A typical rebuild kit includes:
- Lid O-ring
- Two post O-rings
- Two dip tube O-rings
- Two poppets
A full rebuild kit costs $5 to $10. Plan on rebuilding every used keg you buy. It's a 10-minute job and ensures you start with known-good seals.
What used corny kegs cost
Prices have crept up over the years as the supply of decommissioned soda-industry kegs has gradually been absorbed. Expect to pay:
- Reconditioned 5-gallon ball lock: $50 to $80
- Used "as-is" 5-gallon ball lock: $30 to $50
- Pin lock equivalents: Usually $5 to $15 less than ball lock
- 3-gallon kegs: Similar to or slightly less than 5-gallon
"Reconditioned" usually means cleaned, pressure-tested, and rebuilt with fresh O-rings. "As-is" means you take it as it sits and do the work yourself. If you're comfortable replacing O-rings (and you should be — it's basic keg maintenance), as-is can be a much better value.
The takeaway
Cornelius kegs are the easiest entry point into kegged homebrewing. They're cheap on the used market, parts are dirt cheap, and the soda-industry surplus that flooded the market in the 1990s means used inventory is still healthy decades later. Pick a connector style (ball lock or pin lock), commit to it, and don't be afraid of "as-is" kegs as long as you're willing to rebuild the seals.
