Put a Spigot in a Glass Carboy: Projects

spigotThe idea for this issue’s project came from a BYO reader. Ronald E. Kingery of Green-town, Indiana wrote to me a while back, asking, “Has there ever been a project in a past issue that dealt with adding a tap (or spigot) to a glass carboy? I am very interested in attempting to do this so I can get completely away from siphoning.”

Ronald, thanks for a great idea. As often as I’ve looked at half-gallon jugs for brewing “sun tea,” I’ve never thought of applying this idea to a carboy. Now that I think of it, the idea gets even better.

You could use such a carboy as a bottling bucket or secondary fermenter. When it comes time to transfer your beer, you could do so with just a turn of the valve. Using the carboy as a primary fermenter would not be advisable, however, as “gunk” would likely fill the intake part of the spigot during the vigorous primary fermentation. The valve is, by necessity, placed high enough to avoid transferring the sediment. However, you will have to tilt the carboy at the end of your transfer to avoid leaving behind an excessive amount of beer.

I went to Delphi Creativity Center (formerly Delphi Stained Glass) for assistance on this project. Delphi is an internationally renowned supplier of glass-working supplies and is, oddly, less than a mile from my office. Store manager George Ayars offered to do the drilling and teach us what we need to know to successfully and safely complete this project. Having broken three fermenters in the last few months (don’t ask), I was very appreciative! Before we got started on the drilling, I asked George, “What is glass?”

“A very mysterious material, mostly made of silica sand, soda ash, perhaps some colorant and some substances to make it flow better,” George said. Glass behaves like a supercooled liquid. That’s why when you break glass, you have sharp pointed shards radiating from the point of impact. (Think of thin ice in a pond or your own experience with a misguided ball penetrating a window.)

The Corning Museum of Glass ( says: “Glass is a state of matter. Glasses combine some properties of crystals and some of liquids, but are distinctly different from both. Glasses have the mechanical rigidity of crystals, but the randomly disordered arrangement of molecules that characterizes liquids. Glasses are usually formed by melting crystalline materials at very high temperatures. When the melt cools, the atoms are locked into a random (disordered) state before they can form into a perfect crystal arrangement.”

When you “break” glass — window glass or stained glass — you control the breaking point by creating a score or scratch to break the surface tension. The next step is to bend the glass away from the score. The glass will then break or tear away from the scratch. With a flat sheet of glass, it’s easy. When cutting a bottle, it’s much more difficult, as you can’t bend the cylindrical surface. Fortunately we’re drilling a hole, not attempting to cut one!

So what are the challenges of drilling a hole into a fermenter? “If we start to drill, that hole is a lot like a score or scratch,” said George. “If we apply torque — a sideways force pushing or wedging the glass — it will split or break, fracturing in any direction. Our objective is to drill through completely without torquing the glass or overheating the glass. Heat will cause local expansion and crack the glass.”

This means the drill needs to be kept perfectly perpendicular (or at the same angle) during the drilling. When you drill through, just as with wood, there is usually some chipping. So the practice is to drill an undersized hole and enlarge it. That’s what we did. A better, but more costly, approach is to use a 1″ (25 mm) diamond hole saw, not the 1/2″ (13 mm) one we used. Using the larger hole saw will save half an hour, but double the hardware cost. If you’re making several projects, this is the way to go. Be aware, however, that the bit will only last for drilling three to eight holes.

George suggested we use silicone sealant to secure the spigot or transfer valve; it’s impossible to get the nut into the bottle because the nut is larger than the bottle’s neck. This means sanitizing and cleaning will be both difficult and critical, just as it is in any bottling bucket! In either case, the design of the transfer valve makes it difficult to thoroughly clean all surfaces. My solution is to point the discharge valve up, attach 3″ (75 mm) of tubing and fill the bucket or fermenter with cleaner until the valve is completely filled.

Step by step

Start by deciding where on your carboy you want the spigot. We measured 3-1/2″ (90 mm) up from the table and marked diagonal lines between the webbing of a five-gallon fermenter. (If you choose a larger, smoother bottle, mark centered between the seams or upon a seam.) Having the hole at 2-1/2 to 3-1/2″ (65–90 mm) will allow use as a fermenter or bottling bucket; fermenters need more depth for yeast and trub. If you plan to use your modified carboy is strictly as a bottling “bucket,” select a height that is 1 to
1-1/2″ (25-38 mm) above your usual yeast depth to avoid pulling dead yeast into your bottles.

For safety, you must wear safety glasses or goggles. You may wish to wear leather or other non-slip gloves and a shop apron as well as a long-sleeved shirt. In the unlikely event the bottle breaks, it will most likely chip. This is not a problem if it’s small.

Alternately, a crack may develop. If so, stop drilling and discard the carboy. Try it again if you have the a spare bottle. George was impressed with the glass thickness of a typical fermenter and considers it unlikely you’ll fracture one unless you add torque (for example, by tilting the drill.) A small chip is more likely and can usually be covered by the silicone sealant.

Chuck a diamond-coated glass drill (hole saw) of at least 1/2″ diameter into a variable speed drill. The variable speed part is important. You will need to start the scoring very slowly. This can’t be done at high speeds.

Build a watertight dam of modeling clay around the hole’s center; this will hold cooling water. In other words, a kiddy pool filled with water atop the carboy wherein you dip the drill, not tiny children.

Start drilling at your drill’s slowest speed and at an oblique angle. “The glass is so hard and smooth the bit skitters. A 60° angle is a good starting point,” George says. All you’re trying to do is create the smallest scratch; a light touch is critical. Once you get a slight indentation or groove, you can increase speed and straighten the drill and bit to perfectly vertical.

Use “no” pressure — ounces, not pounds. Only the diamond can cut the glass. Once you’re cutting with the entire surface — as when the drill is upright — you may increase drill’s speed to maximum. Cutting the first hole with a hole saw, of either size, takes about fifteen minutes.

Water is critical for cooling and to prevent glass dust and fragments from infiltrating your lungs. Glass fibers cause silicosis, an extremely wicked disease. Keeping the glass fragments wet will prevent problems. You could also wear a particle mask for more protection.

Continue to cut, using the lightest pressure and supporting the drill, until the inside face is penetrated. You’ll know when this has occurred because you’ll see water drops hit the bottom. Keep adding water!

What happens next depends on your bit size. If you’ve used the larger 1-1/16″ bit, you’re all done except a light dressing with sandpaper.

If you used the smaller, less expensive bit, you’ll spend the next half hour enlarging the 1/2″ hole to its final 1 1/16″ diameter. You may use the side of the original hole saw, or a solid bit (available from Delphi — it’s the bit we used.) To cool the enlarging bit, keep a well-wetted sponge in contact with the bit at all times. If you’re not dripping, wet the sponge.

Dremel has diamond bits available, but for once I’d not recommend this option as it would take too long to cut the hole. And if you already have a stained glass grinder you may — MAY — be successful in enlarging a hole to size. Last, if you own a drill press and can secure the bottle while applying coolant, it might be the best solution as long as you keep pressure light.

Once the hole is completed, you’ll need to mount the spigot or transfer valve. Use clear silicone sealant and apply a thick ring around the hole. Place the spigot into the hole and gently press it into the silicone. Press until the lip of the spigot either touches the glass or comes close. Our glass bottle was about 3/16″ thick and should not crack from the torque applied by opening the tap. However, I will always use two hands — one on the spigot, one on the tap lever — when using the valve.

I used a silicone RTV adhesive sealant. RTV stands for Room Temperature Vulcanized — it cures at room temperature and once cured is quite inert according to the manufacturer. While not NSF rated, some silicone sealants are USDA authorized “for use in federally inspected meat and poultry plants,” according to a Materials Safety Data Sheet from Permatex. Those are Permatex 16B/81158 (Black) or 66B/80050 (Clear) in 3-ounce tubes. An alternative product is Permatex Plastic Bonder 82565. All are available retail at NAPA and some other auto-parts stores.

If the directions are followed, even loosely, the possibility of flying glass is pretty small. Explosions are impossible — there is no pressure, unlike a bottling line. And the glass is very thick.

For what it’s worth, neither of us used gloves or face masks. George considered it unnecessary to wear protective gear based on decades of experience with glass breaking.