Every wonder if you could make a water tight square keg? Check it out!

[Sirfrito]

Ever wondered if a square keg would work? This clever patent shows that it can be done. No indication how much pressure it could safely handle. It would need to stay less than 5 ATM with a good pressure release valve and be safely tested first.

https://havencrest-microbrewery.blogspot.com/2016/08/rectangular-container-for-aging-of.html

 

[timdillon36]

A square keg will not work. It might have the area you want but will not hold any volume. A cube shape keg on the other hand could be built to hold any volume you want.

A five gal cube would be roughly 10x10x10. If you want to test that at 75psi that would be the same as placing 7500lbs on a 10x10 plate that is only supported on the edges.

Make the plate thick enough and it will only bow a little, make it thin enough to carry around and when you put pressure to it. It will become round.

You don't see square kegs for the same reason you don't see square above ground pools or square balls or balloons. Or square hoses or pipes. Pressure makes things round.

OK, I'll stop.

 

[day_trippr]

Honest to Flying Spaghetti Monster, I'm almost tempted to try to build one of those...

Cheers! (Wait....That'd be crazy! Never mind... )

 

[jddevinn]

Flat walls make very bad pressure vessels!!!

 

[GPP33]

Minor detail I know but yes, it would work. Generally AGING vessels don't hold pressure.

Rectangular container for the aging of alcoholic beverages

 

[Sirfrito]

So, I would only get it to 15 PSI. With suitable thickness, I might be still tempted to give it a try. The question for me is would it be air tight enough to hold CO2 to prevent oxidation, maintain carbonation and dispense adequately.

 

[mattd2]

So, I would only get it to 15 PSI. With suitable thickness, I might be still tempted to give it a try. The question for me is would it be air tight enough to hold CO2 to prevent oxidation, maintain carbonation and dispense adequately.

The real question for you is why is your heart set on a cube? A cube pressure vessel will not only be thicker to handle the same pressure as a circular/hemispherical (keg shaped) one but will also be more difficult to manufacture in general due to bending thicker material and doing right angle bends, etc.
Roughly you will still get approx. 80% of the same volume into a tube shape compared to a cube. Is that extra 20% worth it?

 

[day_trippr]

There's no "bending".
There's a metric crapton of mitered joints and an enormous dependency on hydration sealing it up, but no "bending"...

Cheers!

 

[mattd2]

There's no "bending".
There's a metric crapton of mitered joints and an enormous dependency on hydration sealing it up, but no "bending"...

Cheers!

Sorry was not referring back to the original article and meaning a vessel capable of holding 5 atm of pressure (as stated in the original post). No way would I trust a wooden crate with 5 atm of pressure!
The original patent is for a replacement for wooden wine casks/barrels (as what I think GPP33 was referring to)

 

[GPP33]

So, I would only get it to 15 PSI. With suitable thickness, I might be still tempted to give it a try. The question for me is would it be air tight enough to hold CO2 to prevent oxidation, maintain carbonation and dispense adequately.

You want to make a wood keg that'll hold 15 psi? Let's say each face is 12" by 12", that's 144 square inches which will see 2,160 lbs, assuming you can get it anywhere near air tight (which won't be easy).

 

[JohnSand]

I think it can be done. Oak is very strong and stiff. The short thick pieces you would use are not going to flex. They can be edge fastened for strength and tightness, using through-bolts or drifts.

 

[wilserbrewer]

Sorry don't have the link, but I recall a guy making a stainless steel cube shaped keg to fit in a mini fridge to maximize volume.

He was involved in contact manufacturing somewhere in the Middle East where beer and kegs don't really exist. He also had access to excellent material and tooling / welding.

They did a beautiful job, but to pay to fab one would likely be a thousand bucks unless you can DIY

 

[GPP33]

I think it can be done. Oak is very strong and stiff. The short thick pieces you would use are not going to flex. They can be edge fastened for strength and tightness, using through-bolts or drifts.

I'll bet you a beer that they'll flex enough to leak pretty bad, unless you build it uselessly small.

Sorry don't have the link, but I recall a guy making a cube shaped keg to fit in a mini fridge to maximize volume.

He was involved in contact manufacturing somewhere in the Middle East where beer and kegs don't really exist. He also had access to excellent material and tooling / welding.

They did a beautiful job, but to pay to fab one would likely be a thousand bucks unless you can DIY

Metal is a whole different ball game. If there was a good reason to build one it could be a cool project.

 

[jddevinn]

FYI, here is the full patent. Seems doable... but the goal is long term aging, ie replacing an aging barrel. Beer is not specified, just "alcoholic beverages"

View attachment USA104093099.pdf

 

[lupulinaddict]

Isn't there something about wood being porous that it allows oxygen in, or maybe out, in wine making? I thought there was something other than flavor as a reason winemakers use wooden barrels instead of a stainless vessel.

I think op needs to build one and test it!

 

[GPP33]

I'm still trying to figure out how a wood box is deserving of a patent.....booze has been stored in wood containers for eons, goods have been stored in wood boxes for eons, somehow storing booze in a wood container in the shape of a box is groundbreaking?

 

[JohnSand]

I'll bet you a beer that they'll flex enough to leak pretty bad, unless you build it uselessly small.

I'm sure someone could calculate the necessary scantlings based on modulus of elasticity. I will neither do the math nor build the cube, so you are not risking the beer. But if the OP builds one, you should donate a beer to the thirsty.

Isn't there something about wood being porous that it allows oxygen in, or maybe out, in wine making? I thought there was something other than flavor as a reason winemakers use wooden barrels instead of a stainless vessel.

I think op needs to build one and test it!

Some woods are more porous, some less. White oak, used for wine barrels, is not porous to liquids, and probably not much to air if thick enough. I have an original wooden beer keg, round, of course. It has staves about 1.25" thick, and some kind of finish on the inside. I believe the finish was to protect the lager from oak flavor, more than preventing oxidation or leakage. I realize that a round vessel holds pressure more easily, but a small square one with the staves fastened together and the corners reinforced on the outside would be remarkably stiff and strong.
My knowledge of wooden construction comes from a lifetime studying wooden boats, and 25 years of owning and repairing them. I am not a cooper, but I did stay at a Holiday Inn Express once.

 

[GPP33]

Someone needs to build this thing. I'd try but I know my wood working skills aren't up to par and I'm pretty sure the wood at Home Depot isn't straight enough.

I kinda want to build a stainless one but I don't really have a use for a square keg, more curiosity than anything at this point.....

 

[JohnSand]

Looking at the wooden keg today I realized that the top and bottom are flat, and held half a barrel at serving pressure and much more, because they were probably shipped warm. This keg has fittings in the top and side, I don't believe it was just for hand pulled cask ale. So I'm sure that a cube can work. I do have the woodworking skills to do it, and probably the material, but not the need.

 

[GreenMonti]

You want to make a wood keg that'll hold 15 psi? Let's say each face is 12" by 12", that's 144 square inches which will see 2,160 lbs, assuming you can get it anywhere near air tight (which won't be easy).

Glad you posted. I was about to say this same thing.

Folks have to realize it's total surface area times the pressure being applied. Which equals big time force.

 

[JohnSand]

The lid of the wooden keg is 12" diameter, 113 square inches, 1695 lbs at 15psi, much much more at warmer temps. It consists of five pieces about 1.5" thick, edge nailed and restrained by the barrel band. The parts have a thin shaving of light wood between them to act as caulk. This was used to transport, store and serve beer for years, maybe decades. (The barrel, not the beer)

 

[mattd2]

The lid of the wooden keg is 12" diameter, 113 square inches, 1695 lbs at 15psi, much much more at warmer temps. It consists of five pieces about 1.5" thick, edge nailed and restrained by the barrel band. The parts have a thin shaving of light wood between them to act as caulk. This was used to transport, store and serve beer for years, maybe decades. (The barrel, not the beer)

When beer was stored in wooden barrelsit was not carbonated like today's beer. Read up on real ale - one of the reasons people think the British like their beer flat and warm

 

[GreenMonti]

The lid of the wooden keg is 12" diameter, 113 square inches, 1695 lbs at 15psi, much much more at warmer temps. It consists of five pieces about 1.5" thick, edge nailed and restrained by the barrel band. The parts have a thin shaving of light wood between them to act as caulk. This was used to transport, store and serve beer for years, maybe decades. (The barrel, not the beer)

Being a circle each "piece" or stave is progressively stronger, the closer it gets to the edge. The weakest piece would be the center piece.

It would be interesting to know how much lateral pressure the wood exerts on itself from being wet?
I also wonder, since only one side of the wood is wet.....does that make the wood expand more so on the inside causing it to naturally bow inward given it more strength? From the outside it would look concave.

 

[JohnSand]

Matt, I thought that too. But I've since read that metal kegs only became prevalent in the 1950s. My keg may be as young as 70 years old. This keg didn't hold real ale, almost certainly American Lager. It is a Ruppert's Brewery keg. Our fathers and grandfathers drank beer quite similar to today's macro lager. My dad was born in '33. He must have had tap beer from wooden kegs. (He started drinking beer at about 14). My grandfather was born in 1910. They are both gone now, but the lager revolution occurred long before they were born.

 

[JohnSand]

Monti, the wood can exert great pressure from swelling. I suspect that it would have some equilibrium in moisture content, even though the inside is wet. The planking of a boat has a high moisture content, I've observed them wet and dried out, the planks seem to swell and shrink evenly. This keg also has a finish on the inside, pale yellow in color on the top and bottom. It may be shellac. I think it was applied to keep the light colored and flavored lager from getting any taste from the oak.

 

[GreenMonti]

Matt, I thought that too. But I've since read that metal kegs only became prevalent in the 1950s. My keg may be as young as 70 years old. This keg didn't hold real ale, almost certainly American Lager. It is a Ruppert's Brewery keg. Our fathers and grandfathers drank beer quite similar to today's macro lager. My dad was born in '33. He must have had tap beer from wooden kegs. (He started drinking beer at about 14). My grandfather was born in 1910. They are both gone now, but the lager revolution occurred long before they were born.

Your still speaking to a barrel and not a cube.

 

[GreenMonti]

Monti, the wood can exert great pressure from swelling. I suspect that it would have some equilibrium in moisture content, even though the inside is wet. The planking of a boat has a high moisture content, I've observed them wet and dried out, the planks seem to swell and shrink evenly. This keg also has a finish on the inside, pale yellow in color on the top and bottom. It may be shellac. I think it was applied to keep the light colored and flavored lager from getting any taste from the oak.

Interesting.
Thanks for the info.

 

[Sirfrito]

I know let's get the Myth Buster team out of retirement and get them to have a go...

 

[JohnSand]

Your still speaking to a barrel and not a cube.

Right. The structure of the sides is completely different, the geometry too. And I know that boatbuilding is not a parallel, as the pressure is inward among other reasons. I do find a reasonable comparison in the sides of the cube and the flat top of the barrel. The hoops probably exert a lot of force when driven on, which is why I think that through-bolts edgewise would be necessary. I'm halfway tempted to try it, but my old car, old boat and old house need work more than I need a wooden cubical keg. Or more than anybody does. But it is an interesting discussion.

 

[GreenMonti]

Right. The structure of the sides is completely different, the geometry too. And I know that boatbuilding is not a parallel, as the pressure is inward among other reasons. I do find a reasonable comparison in the sides of the cube and the flat top of the barrel. The hoops probably exert a lot of force when driven on, which is why I think that through-bolts edgewise would be necessary. I'm halfway tempted to try it, but my old car, old boat and old house need work more than I need a wooden cubical keg. Or more than anybody does. But it is an interesting discussion.

It sure is.
I didn't bother to get in depth with the op schematic. However, your barrel has a dado joint where the end caps go into the side staves, right? That would add a whole bunch of strength.

If one bolted a dado joint on this square design, I think I'd worry about splitting the ends of the wood over time.

 

[JohnSand]

Not exactly. The lid has a beveled edge, that fits into a matching groove in the staves. The internal joints on the lids are flush, with thin shavings between the parts. They are held in place by edge nails, but made tight by the pressure from the hoops. If I were building one, all joints would be flush, the corners at 90', pressure applied by edge bolts. The bolts could be left a bit long for adjustment.

 

[GreenMonti]

Not exactly. The lid has a beveled edge, that fits into a matching groove in the staves. The internal joints on the lids are flush, with thin shavings between the parts. They are held in place by edge nails, but made tight by the pressure from the hoops. If I were building one, all joints would be flush, the corners at 90', pressure applied by edge bolts. The bolts could be left a bit long for adjustment.

I believe that's called a dado joint. If I remember right, a rabbit joint is on the edge of a board. I suppose I could google it.

How do you mean edge bolts?

 

[JohnSand]

I mean bolts that run through the pieces from side to side, through the width rather than the thickness. As if you laid the bolt flat across the plank, but inside. In boatbuilding, rudders, centerboards and centerboard trunks are built this way for strength and water-tightness. Even a modest bolt can apply great pressure. At the corner they would go through the adjacent side in the usual fashion, perhaps with an external reinforcing piece. The joints would have to be finished perfectly flush and smooth. I believe that the very thin slices between the staves are cedar or white pine. Compressed by pressure, and swelling quickly when wet, they help make the barrel tight. In traditional boats this would be cotton driven in between planks.
Sorry if some of my terms are not clear. I am not a pro, and boat carpentry, which I know best, uses different descriptions.

 

[GreenMonti]

Gotcha. Would you go all the way through with the bolts or would you stop part way?

I googled edge bolts in rudders to make sure my mental picture was what you were talking about. I was close. Based on the pics that popped up. From your description I envisioned a bolt going through the whole panel compressing all the planks together. Which would help with any sort of bowing that the panel might want to do once wet.

Edit:
I want to say an engineer at work told me a 1/4" bolt would carry 1,000 or 1,500 lbs. as long as the load was not in shear. Just linear to its length.

 

[JohnSand]

I would bolt them all the way through to seal the joint at the adjacent side too.