Buying a used keg is only half the work. Before you put beer (or anything else) into it, you need to clean it properly. A used keg has unknown history: it may have sat with stale beer for months, been used as a water cooler at a contractor's job site, or been stored in a damp garage for a decade. Every used keg should be assumed dirty until proven otherwise.
This guide covers what to clean with, what to sanitize with, and the actual step-by-step process for both Sankey and Cornelius kegs.
Cleaning vs sanitizing: not the same thing
These get used interchangeably, but they're separate steps with different goals.
Cleaning removes physical soil — beer residue, dried syrup, biofilms, scale, dirt. You can't sanitize a dirty surface, because the soil shields microorganisms from your sanitizer.
Sanitizing reduces microorganisms on an already-clean surface to a safe level. It's a final step done immediately before filling.
You always clean first, then sanitize. Sanitizing a dirty keg accomplishes nothing.
Cleaning agents that actually work
PBW (Powdered Brewery Wash) is the standard in the craft brewing world. It's an alkaline percarbonate-based cleaner that lifts protein, hop residue, and biofilm without being as harsh as straight caustic. Recommended for most homebrew situations. Typical mix: 1 to 2 oz per gallon of hot water.
Sodium percarbonate (the active ingredient in OxiClean Free) is essentially the same active chemistry as PBW at a lower cost. Use the Free version — no dyes, no scents. About 1 tablespoon per gallon.
Caustic (sodium hydroxide / lye) is the industrial standard for commercial brewery cleaning. It works, but it's dangerous to handle, requires careful neutralization, and can damage gaskets if used at the wrong concentration. Most homebrewers don't need it. If you do use it, wear gloves and eye protection.
Acid cleaners (phosphoric, nitric blends) are used in commercial settings to remove beerstone — a calcium oxalate scale that builds up over time and resists alkaline cleaners. If you've got a keg with visible beerstone (a chalky white or grey deposit), you'll need an acid wash after the alkaline clean.
What doesn't work: dish soap, bleach (corrodes stainless), vinegar (too weak), Bar Keepers Friend (fine for cosmetic exterior, but not for sanitary cleaning).
Sanitizers
Star San is the standard. Acid-based, no-rinse at the proper dilution, fast-acting (1 minute contact time), and the residual foam is actually beneficial — "don't fear the foam." Mix 1 oz per 5 gallons.
Iodophor is an iodine-based no-rinse sanitizer. Effective but stains plastic and can leave a slight iodine flavor if overdosed. Less common in homebrew now that Star San is widely available.
Heat (steam or boiling water) is the only sanitizer that doesn't require chemicals. Effective but requires equipment most homebrewers don't have.
Equipment you'll need
- A 5 to 10 gallon bucket for soaking smaller parts
- A long-handled keg brush (for Sankey kegs, you'll need a special spear-removal tool)
- A bottle brush for posts and dip tubes
- A pump sprayer or recirculation pump (optional but helpful)
- Hot water source (warmer is more effective for cleaning)
- Gloves and eye protection
Cleaning a Cornelius keg: step by step
Corny kegs are the easier of the two because the lid comes off completely. For background on the keg type itself, see our guide to Cornelius kegs.
- Depressurize the keg. Pull the pressure relief valve until you hear all gas escape. If the PRV won't actuate, carefully loosen the lid with a partial twist to release pressure before opening fully.
- Open the lid and dump any contents.
- Remove the lid, both posts, both dip tubes, both poppets, and all O-rings. A 7/8" deep socket fits the posts on most ball lock kegs. Pin lock posts require a specific 11/16" or 13/16" socket depending on the model.
- Soak everything in PBW solution. Fill the keg body with hot PBW and drop the disassembled parts (except O-rings) into a separate bucket of PBW. Soak 20 to 60 minutes for routine cleaning, overnight for a neglected keg.
- Scrub the interior with a long brush, paying attention to the bottom corners and the area around the dip tube weld.
- Rinse thoroughly with hot water. Multiple rinses. Any cleaner residue will affect beer flavor and Star San effectiveness.
- Inspect. Run your fingers along the interior. It should feel smooth and slick. If you feel any roughness or stickiness, repeat the cleaning step.
- Reassemble with new O-rings.
- Sanitize. Fill the keg with Star San solution, seal it, shake to coat all interior surfaces and the inside of the lid, then drain. Run a small amount through both posts to sanitize them too.
- Fill immediately. Don't let a sanitized keg sit open for hours.
Cleaning a Sankey keg: step by step
Sankey kegs are harder because the dip tube assembly (the "spear") is held in place under pressure and requires a specific tool to remove. Many homebrewers leave the spear in and clean around it; this works for routine maintenance but isn't enough for a neglected used keg.
- Depressurize. A Sankey keg coupler with the lever down releases pressure. If you don't have a coupler, the spear has a small valve in the center you can depress with a screwdriver — very carefully, after confirming the keg is upright and you're not standing over it.
- Drain.
- If possible, remove the spear. Requires a Sankey spear removal tool. The spear is held in place by a snap ring that requires the tool to compress and remove. Trying to do this without the right tool is dangerous — a pressurized spear under tension can become a projectile.
- Soak with PBW. If the spear is in, fill the keg with PBW solution through the spear opening, seal it, and rock it to slosh the solution through all interior surfaces. Soak 1 to 2 hours minimum, overnight if heavily soiled.
- Drain and rinse repeatedly. Multiple rinse cycles. With the spear in place, you can't physically inspect or scrub the interior, so chemistry and contact time do the work.
- Inspect (if spear removed). Same interior check as a corny keg.
- Sanitize. Fill with Star San, seal, slosh, drain.
- Fill or pressurize with CO2 to keep oxygen out until ready to use.
When a keg can't be saved
Some used kegs are beyond cleaning. Walk away if you find:
- Heavy interior pitting. Pinhole corrosion in stainless usually means chloride exposure (often from harsh cleaners or sitting with chlorinated water for years). Cleaning won't fix it; the metal is compromised.
- Persistent sour or chemical smell after thorough cleaning. If you've done a proper PBW soak and the keg still smells wrong, the porosity of the surface has absorbed contaminants that won't come out.
- Cracks at weld points. Cracks at the bottom dome, post weldments, or spear weld are unfixable for sanitary use.
- Heavily damaged spear (Sankey). Sometimes replaceable, but verify the cost of a new spear before buying.
The used keg inspection guide covers what to look for before you buy — ideally you catch these issues before money changes hands, not after.
A maintenance schedule that works
Once you've got a used keg cleaned up and in service, the ongoing maintenance is simple:
- Between batches: Disassemble, PBW soak, rinse, sanitize, refill. 30 minutes of work.
- Annually: Replace all O-rings whether they look bad or not. They're cheap; failed seals waste beer and CO2.
- Every 2 to 3 years: Inspect the interior carefully for any developing pitting or beerstone. Acid clean if beerstone is present.
A well-maintained stainless keg will outlive you. The single biggest enemy is neglect — beer left to dry inside, or storage with residual moisture. Drain, rinse, and either fill or pressurize-and-store. Don't leave a wet keg sitting open.
