You can use grandma’s canning kettle. You can shell out $300 for a ready-made model with all the bells and whistles. Either will work, but for many homebrewers, there’s nothing cooler than boiling wort in a converted beer keg. Especially if they made it themselves. If you want to save some money and make your own kettle, converting a keg is viable option for the “do it yourselfer.”  

So you’ve bought a keg from RCB, Sabco or the junkyard with the intent of converting it into a brew kettle. Now what? First, if everything looks intact, you’ll need to release any residual pressure and dump whatever remains in the keg.         

A note of caution: If the keg contains residual pressure, the valve could explode from it at life-threatening velocity. There are two safe ways to release pressure: Visit a brewery and use their special (and expensive) valve-removing tool, or drill a tiny hole in the top and let the pressure drop slowly.

Now that you’ve safely vented your keg, it’s time to convert it. It’s important to have your objectives clearly in mind. Do you want to use your kettle for mashing, wort boiling or sparge water? Each objective can be optimized and a compromise can be made if your boil kettle is also your mash-lauter tun. Try to plan your design with easy changeover in mind.

We called William Stewart of Moving Brews in College Park, Maryland (301-779-8609; www.movingbrews.com) for advice on parts and construction. Moving Brews is a respected provider of stainless-steel fittings and other RIMS supplies. Stewart said, “If you have to accommodate a false bottom and a drain pipe for mashing or boiling, obviously that’s more complicated than just installing a drain pipe for sparge water.” A basic installation kit from Moving Brews (and many other homebrew suppliers) includes a coupling, a two or three-inch pipe nipple, a ball valve, and a hose barb.

Keg conversion also depends on what tools you have and what local resources are available. If you know a sanitary welder, you can have all the cutting and fitting done for under $100. (Some sanitary welders may even work for homebrew!) If you prefer to do it yourself, read on.
Taking the top off
    
The first issue is removing the top of the keg and cutting to fit a lid. Buy the lid first. You can find them at restaurant supply stores. (Using the top as a lid is not a good option since experts say it will never fit tightly enough). The pros at RCB recommend using a plasma arc cutter, cutting a hole slightly smaller than the lid and grinding to fit. Common oxygen-acetylene torches should never be used since they will ruin the keg. The alternative is a “Sawzall” and a carbide grit-coated blade, not a high-speed steel blade.

After cutting the hole you need to smooth the edge. Use an electric or air die grinder, preferably with a carbide grinding tool, to shape the hole to the final size. Plasma cutting leaves a film on the inside of the keg that must be removed, but you might want to postpone cleaning until all welding is finished.

Adding the fittings
With the main opening cut, you’ll want to add your fittings: a drain, maybe a thermometer coupling and a sight gauge. Where you put these is up to you, but the consensus is that the drain hole goes close to the keg’s chine, the half-coupling for a thermometer should be installed offset near the mid-point of your normal liquid volume, and the sight gauge should measure minimum and near-maximum liquid volumes. The sight gauge should also be offset. Don’t reinvent the wheel; visit every homebrewer you know and look at their equipment. Ask them what they like, what they’d do differently.

If you have trouble monitoring your sparge water levels, we’d heartily recommend installing a sight gauge. Fermentap, Moving Brews, Granger and other companies sell “weldless” kits — which only require drilling a hole — for under $45. Kits consist of a right-angle fitting into the kettle and a glass tube with protective wrapper that echoes liquid level. The downside to sight glasses is that they’ve definitely been known to break.

An alternative is to have a welder install two short quarter-inch (inside diameter) stainless tubes, bent to a right angle, in the same vertical plane. Connect the two with flexible plastic tubing. It’s not rated for this heat, but you can use it for a couple of brews and throw it out. You’ll see this version in our photos.

Depending on what kind of kettle are you building — sparge, mash or boil — each will have a different siphon tube (drain tube) location. A siphon tube reaches from the coupling to nearly the bottom curve of the kettle. If you use this kettle for boiling wort, you can install the fitting very close to the chine and use a stainless steel or copper “chore boy” metal sponge as a hop filter. In addition, sturdy metal false bottoms are available from Sabco, Moving Brews and other suppliers to remove hops. For a boil kettle, almost any size false bottom and siphon tube would do. Or you could pull the siphon tube out and simply whirlpool your wort and drain from the coupling ball valve.

Making a mash tun     
If you are making a mash tun, other decisions must be made. A mash tun needs as much drain volume (surface area of the false bottom) as possible to minimize stuck mashes. So the false bottom needs to be equal to the kettle diameter and fit tightly. You may want to mount the drain a couple of inches higher on the side of the kettle. Of course, this interferes with stirring the mash, as would positioning a thermometer probe in the middle of the mash. So you’ll have to reach a compromise, like having the siphon tube turn a right angle as it enters the center of the false bottom instead of a gentle (and high into the mash tun) arc. Whatever you do, we’d suggest a very bold mark on your mash paddle so you don’t hit the thermometer probe, smash the siphon tube, or disturb the mash within a few inches of the false bottom.

Kegs are of uniform size and appropriately sized false bottoms are widely available for mashing or holding hops back ($30 and up). Many mash-tun false bottoms come in two pieces, attached by hinges. Most have a hole drilled in the center to fit your siphon tube. You’ll have to discuss this with the vendor.

The size and shape of the holes in the false bottom of mash tuns is a highly debated issue. Some insist that slitted stainless steel should be used, while others assert that holes of a particular size and frequency work best. Like “dry yeast versus liquid yeast” debates, the decision is up to you. Just be sure to support the metal; it isn’t meant to carry 40 pounds of grain without flexing.

Once you’ve made all your decisions, it’s time to drill holes for your nipples or couplings and weld or braze them into your keg. If you are TIG (tungsten inert gas) welding your couplings you’ll get a cleaner weld if you attach the kettle lid and flood the vessel with inert gas. Any welder familiar with sanitary welding will know this.

Some more advice from Stewart at Moving Brews: “Before you leave the welder, make sure the piece is watertight and that you can thread things into the threaded nipples or couplings. It’s no fun to find a pinhole leak or victimized thread.”

Now it’s time to clean your kettle with strong cleaner. Some welders will have caustic and acid tanks for cleaning. You need to get the grunge out of the kettle and fittings. I recommend a cleaner called PBW from Five Star (800-782-7019; www.fivestarchemicals.com).
     
The siphon tube     
Finally we come to the siphon tube and its construction. Most of the siphons we’ve seen are made with a compression-fitting at one end and a curved copper tube reaching to the kettle bottom.

We think a flare fitting would be a better choice. Compression fittings are meant to be tightened once and seldom taken apart. Flare fittings are removable and may leak. But — what the heck — who cares if the fitting leaks inside the kettle? Also, I built a flare-fitting siphon tube because I have flare tools.

Either way, start by deciding where you want the suction end of the tube. Bend the tubing (soft tubing, not regular copper pipe for water lines) in a nice soft arc and 1 to 2 inches overly long. Then place the tube inside the kettle, screw the flare (compression) fitting into the coupling and measure precisely where the siphon belongs. If you have a false bottom, you’ll have to install it as well. You can always bend the pipe a little more and remove a little extra metal.

Wrapping it up    
You’re finished. The kettle is atop your burner, happily heating gallons of liquid. What did it cost you? Keg: anywhere from zero to $80 (see “Obtain the Keg” on next page). Welding or brazing will cost at least $10 (for brazing supplies) to $100 for a multi-fitting keg (cutting and shaping the opening, a siphon, sight gauge and thermometer). Parts from Moving Brews or other supplier will cost $38 ($28 stainless ball valve, $4 coupling, $3 3-inch nipple, $3 half-coupling) plus $25 to $40 for an optional thermometer and $5 for the homemade siphon. A false bottom will add another $20 to $90 to your expense list.

By way of contrast, a readymade deluxe mash-and-boil kettle from Sabco that includes a new keg, siphon, stainless steel ball valve, thermometer, false bottom and lid is $365 plus shipping.

At $55, the total cost for the cheapest do-it-yourself option we described, the attraction of a homemade converted keg kettle is obvious. At $290 or more, plus time and labor, store-bought might be a better deal. In any event, have fun with your project and be safe.
     
Thom Cannell is a longtime homebrewer and a veteran freelance automotive writer and editor.