Brewery Keg Conversion

Many people have written on the subject of converting beer kegs into kettles for homebrewing. I have no special insights to add to what others have written, but I did take a lot of pictures.

I found a decent stash of 50L kegs at a scrap metal dealer, Madison Steel in Kitchener, Ontario. Many of the kegs appeared to me to be in excellent condition. They all held pressure (be careful when testing this; I used a screwdriver, wrapped in a rag to block the stream of disgusting stale beer.) One had scarcely a scratch on it. I don’t know why they were scrapped. But I’m glad they were, because I got to buy them for their value as scrap, which isn’t very much (around CDN$15). I bought a whole bunch of them, which will eventually all be converted into kettles for myself and some brewing friends.

Removing the Top

Unmodified beer keg

So, here’s your basic, unmodified beer keg. This is the first one I bought, and it isn’t quite as nice-looking as some that came later:

The first, and most difficult step is to get the top off. Some people have suggested using a “sawsall”, and a lot of sweat. I happen to have a coworker who has a plasma cutter. A plasma cutter makes the job quite easy. The hard part is keeping a steady hand and following the line you marked on the lid, which is hard to see with the welding glasses on. I have no pictures of that process, but here’s the finished result, and a close-up of the cut the plasma cutter makes:

Keg with cut

Keg cut detail

We did a little test of the cutter inside the circle we intended to cut, just to get a feel for how the cutter would work. Here’s the one new insight on keg-conversion that I can give. When we started to make that first hole with the cutter, we were suddenly blasted with a spray of disgusting stale beer. When we stopped laughing, we tried to figure out what happened. The beer, after all, is at the bottom of the keg, and we were cutting on the top. Eventually we figured it out (but not before getting blasted with beer for a second time). And here is the advice: when making the first hole with the plasma cutter, make sure the valve on the keg is closed. I had the valve slightly ajar from when I released the pressure earlier. Now, a plasma cutter has a stream of compressed air, with a plasma arc. The plasma arc melts the metal, and the compressed air then blows the molten metal through the other side of the cut. Normally, a keg is completely sealed, and your first puncture will actually pressurize the inside of the keg. Since our keg valve was slightly open, what happened was the air pressure actually pushed beer up the keg’s dip-tube and out the valve opening, and all over us. Make sure the valve is closed, and you won’t get covered in beer.

Some people have suggested that the molten metal blown into the keg could weld itself to the bottom. In my experience, that didn’t happen. But as a precaution, you could fill the keg with an inch of water before cutting.

So, now we’ve got the opening cut into the top of the keg, and the valve and dip-tube removed:

Keg insidesKeg top

Save the dip tube, it may come in handy someday. I held onto them for years, until I realized I could use one as the mechanical shield around a glass sight gauge.

The inside of the keg is a little bit yucky. Breweries clean them with a high-pressure blast of powerful chemicals. We have to rely on elbow grease. At least with the top cut off, it’s possible. I used some PBW (Powder Brewery Wash) from Paddock Wood, it’s quite good. (Paddock Wood is no longer running their web-store, they’ve converted into a microbrewery.)

Jagged edgesThe plasma cutter actually leaves quite a nasty jagged edge on the inside of the cut. It has to be ground off. I used an angle grinder. It makes a terrible racket, wear hearing protection.

All that being said, this guy has a pretty fine approach, which I’ll probably try in the future.

Plumbing the Keg

So, now we’ve got a basic 50L stainless steel kettle, for a fraction of what it would cost to buy one. But for brewing use, we need some more work. It needs some plumbing. You may need to decide what use the keg will be put to at this point. Typically, it will be a hot-liquor tank, mash tun, or boiling kettle. So far, I’ve made an HLT and a boiling kettle. The required plumbing in each case will be different, but for starters I install at least one 1/2″ pipe-coupling, near the bottom of the side wall. That basic fitting can be basis for any of the three applications. In some kegs, I installed two pipe couplings, 90° apart. The second coupling can accommodate a thermometer and/or sight gauge.

I obtained stainless pipe-couplings at the Desco Plumbing and Heating Supply store in Cambridge, Ontario. The pipe-coupling should be welded to the side of the keg, so that it is flush with the inside wall, and protruding on the outside. Installed that way, you have maximum flexibility in what you can do with the kettle. Plumbing can be installed on either the inside or outside, or both.

I drilled a hole in the side wall of the keg, just above the bottom, using a bimetal hole-saw. The hole made by the hole saw was slightly too small for the pipe-coupling to fit, so I had to enlarge the hole slightly with a Dremel and grinding stone. It was somewhat laborious, but the result was that the pipe-fitting could almost be press-fit into place.

At this point, it was necessary to enlist the aid of a professional welder. Welding stainless steel, especially thin stainless steel, is a skill that I will likely never have. But a professional welder can do it in moments, for only a small charge. Make sure the welder understands this is a food-grade application and uses a suitable filler rod (containing no cadmium or anything nasty like that). The ultimate for this application would be a “sanitary” weld, where both sides of the weld are blanketed with inert gas during the welding process, and the inside is ground smooth and polished. But that’s probably overkill, unless you’re going to use the keg as a fermenter. But you should at least try to have it welded both inside and out. If you only weld one side, the other side will be left looking nasty and the gap between the keg wall and the pipe coupling will be a trap for gunk.

I took my kegs and pipe-couplings to Grand Valley Specialty Welding in Kitchener. He didn’t do sanitary welds, but he did weld both inside and out, and it wasn’t too expensive.

At this point, you have a basic “universal” kettle. Your application will determine what fittings you install on the pipe-coupling. 1/2″ pipe fittings are commonly available, at least in brass. Stainless steel fittings are much more expensive and harder to find. If you use brass (I did), see this link for how to “pickle” the brass to remove lead from the surface.

Universal kettle

Most applications are going to require some plumbing on both the inside and the outside. On the inside, because the pipe-coupling is a few inches higher than the concave bottom of the keg. You at least need a bit of tubing on the inside to reach to the centre of the bottom. And generally you’ll want a valve on the outside. You’ll typically also need a “close nipple”, to connect a female ball-valve to the female pipe-coupling on the keg. I got the nipples and full-port ball valves in stainless from Desco again. More expensive than brass, but not a deal breaker. Naturally, Teflon pipe-tape must be used to get a good seal.

Kettle valve - parts

Kettle valve

Plumbing with Flare Fittings

For the inside plumbing, the first thing I put in is a 1/2″ MPT (male pipe thread) to 3/8″ MFL (male flare) adaptor. Flare connections can be easily assembled and disassembled, but pipe thread is a pain to deal with, so this adaptor is permanent.

In theory, you could use a conventional compression fitting, but they don’t really handle repeated assemble/disassembles very well.

I’ve written a short page about how to use flare fittings.

Plumbing for a Hot Liquor Tank

The internal plumbing for the HLT is simple: just a drain tube. I wanted it to reach right to the bottom of the keg to suck out every last drop. It’s just a piece of 3/8″OD copper tubing, with a flare and flare nut at one end, and bent to the appropriate shape.

In addition, I have also added a glass sight gauge to my HLT, connected to a second 1/2″ pipe coupling installed 90° away from the drain fitting. This makes it easy to measure out specific volumes of water.

Plumbing for a Boiling Kettle

For the boiling kettle, I wanted a drain manifold on the inside. The idea is to avoid picking up the hops and trub when draining the kettle into the fermenter. I made a slotted drain mainfold out of 3/8″OD copper tubing. Then I bent the copper tubing into the desired shape: a ring around the centre of the bottom of the kettle.

A copper tee was used to bring a single branch off the ring manifold and up to the flare connection. The tee was actually a barbed tee for PEX tubing, but it happened to be almost exactly 3/8″ on the inside, close enough for solder to work.

I test fit it many times to make sure the manifold would lie close to the bottom of the kettle when installed on the flare fitting. When I was satisfied with the fit, I used my Dremel with a cut-off wheel to cut many small slots on the bottom side of the manifold.

The manifold goes around the center of the concave bottom, but not to the center. The theory of this was that after boiling the wort, I could whirlpool it, forming a mound of trub in the centre, and the manifold would drain clear wort from around the outside. In practice, the first time I used this system, the whole thing clogged up something awful with hop-pellet gunk, and I was forced to use a siphon instead. The next time I tried it, I used a mesh bag for the hop pellets. I used one of the nylon mesh bags sold at pet shops for aquarium filters.

Later, Whirlfloc tablets also clogged it up, forcing the siphon again. On the whole, it’s not been very successful.


St. Patrick’s
Removing lead from brass fittings
Welding stainless
Paddock Wood

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