The Nitrog-inator

I may not be Dr. Heinz Doofenshmirtz, but I've been known to whip up an -inator from time to time. No, I don't mean a doppelbock, though I'd like to at some point. I mean a contraption. A thingee that does something. None of them ever conquered the tri-state area, and not all of them have been particularly successful, but when it comes to homebrewing, most of them have worked out pretty well. I attribute this to the wealth of knowledge out there on the various homebrewing forums as well as the YouTubes. So far, I've built two kegerators, one based on a cheap fridge that was living in my house when I moved in, and one based on a Danby DAR125SLDD mini-fridge I bought online. I've also wired up a Control Products TC-9102D-HV high voltage dual-stage digital temperature controller, and assembled my all-electric brewery, including soldering together temperature sensors, adding twist-lock plugs to pump cords, modifying kettles, re-sweating a leaking chiller joint, and so forth. It's been a journey, with a lot of learning.

So when I was casually browsing Craigslist one day and saw a used mini fridge (a Kenmore 564.95499400) with no freezer for not very much money, and remembered that I was planning on brewing a Dry Irish Stout for St. Patrick's Day, I jumped at the opportunity. I want to put that stout on nitro!

Nitrogenated Beer

First a little information about nitrogenating beer. Many people are familiar with ordering a beer — usually a dark beer like a stout or porter — "on nitro". While it is stored in a nitrogen cylinder, the gas used to dispense such beers is not just nitrogen. It's usually a gas mix called "beer gas" or  "beer mix", a (roughly) 3:1 mix of nitrogen gas and carbon dioxide. While we all appreciate the pretty cascade of bubbles and the creamy head produced by the nitrogen coming out of solution so rapidly (it's not particularly soluble in water), the original purpose of beer gas was to mimic cask ale. Cask ale tends to be served warmer, with much lower carbonation than most beer. Traditionally, a cask is opened, and then served either using gravity, or hand pumped with a beer engine. The problem with cask ale is that once you open the cask, you expose the beer to oxygen, which means you need to drink up the beer quickly before it stales and winds up tasting like wet cardboard. There are other solutions to this problem, including "bleeder valves" that replace the consumed beer with a blanket of carbon dioxide at atmospheric pressure. But in order to push the beer out of a keg without a hand pump, you need some pressure. Thus the nitrogen. Once the beer is out of the keg, it makes its way to a specially designed stout faucet which has a restrictor plate inside with lots of tiny holes through which the beer is forced. This knocks much of the gas out of solution and creates the cascade and the creamy head and all the magic.

The Build

While the inspiration to build this new kegerator was putting beers on nitro, pretty much every single thing about this build applies to a normal, CO₂ kegerator. The only difference is the way the regulator hooks up to the cylinder, the cylinder itself, and the faucets. And maybe the fact that you might have to spend more time balancing the lines on a CO₂ kegerator—on this one, 95% of the line resistance is in the restrictor plate in the faucet. That said, I'm still using about 7' of tubing, on the off chance I want to convert this to a normal kegerator in the future.

The fridge in its (mostly) initial state.

This will hold two kegs quite nicely.

Modify the Door

Mini-fridge doors have these built-in shelves on them. They get in the way. They must go. Older mini-fridges have the inside door liner attached with screws, usually under the rubber gasket (just peel it back from the inside). These are the best. Newer fridges just have the doors glued on. These suck, as you have to cut the door off with a Dremel or similar. Not fun. 

Door liner removed.

This door was secretly a Seahawks fan.

Once you have the liner off, you can measure how big of a piece of flat plastic you'll need to replace it. I went over to TAP Plastics and had a piece of acrylic custom cut for something like $13. Then I just placed the door liner over it, marked the holes with a sharpie, and drilled away. Screw it back on with the door gasket et voila! One thing to note is that usually the light switch is operated by the door liner hitting a switch inside the fridge. You'll need to either tape that switch down, or, better, just remove the lightbulb. Otherwise the light will run constantly and warm the top of your fridge, which you don't want.

I also switched which side the door opened on so that it would close more easily.

At this point there was nothing I could do until more parts arrived. Fortunately, that did not take long! I ordered these from Keg Connection: An all-stainless two-faucet tower with stainless shanks (included were the liquid disconnects and 7' of tubing for each faucet), two all-stainless stout faucets, gas disconnects, a two-way gas distributor with 1/4" MFL shutoffs with integrated check valves, a nitrogen regulator, and a nitrogen cylinder. Note that the special regulator, cylinder, and faucets are all nitro-specific. The cylinder has to be able to hold the higher pressure at which the beer gas is stored, and the regulator needs to be able to deal with this pressure too.

Parts! Stainless tower with stainless shanks, 7' of hose, liquid disconnects, gas disconnects, 2-way gas distributor, nitrogen regulator and cylinder, and 2 all-stainless stout faucets.

Drilling a Hole In Your Refrigerator

This part is always scary. See, many newer refrigerators have cooling lines in the walls. They are attached to the outer wall of the fridge and turn the whole metal frame into a giant heatsink. If you have a fridge with the big coils outside on the back, this process is a lot less intimidating. If you even nick one of the cooling lines with your drill, you will let all the refrigerant out, and be left with a giant insulated box. There are a lot of ways to figure out where the coolant lines are. You can check the parts diagram which may have them, or you can do what I did and just turn the fridge all the way up, plug it in, and leave the door open. After a while, those coolant lines will start to get hot. There are precise methods that involve painting on a mixture of rubbing alcohol and cornstarch and waiting for the bits near the coolant lines to dry (first). But I'm lazy. I just put my hand on the top of the fridge and felt for warm spots. Once I had a good idea where the coolant lines were, I just drilled behind that. But I drilled carefully, first just through the inner plastic, so that I could poke around in the insulation to feel for any of the lines. I didn't feel any, so I drilled back down through the top to complete the hole. I used a 3" hole saw, but you could get away with a smaller hole, depending on how many lines you need to get through it.

Drilling up through the plastic.

Scraping away the insulation looking for coolant lines.

Drilling back down from the top.

Drilled all the way through!

Once you're safely through the top of the fridge, you also need to drill holes for the bolts that mount the tower. This shouldn't be too hard as usually they are not any further forward (or backward) on the fridge than the extremes of the main hole.

Holes for the bolts drilled.

Once this is done, I like to add some foil tape for two reasons. First, it helps seal off the insulation so that it doesn't absorb moisture from the fridge (thereby losing its insulating ability). Second, it covers up any sharp edges left from drilling through the metal and plastic that might damage the liquid lines (or you). I cut small strips, just long enough to cover the insulation with a little bit sticking over the edge, then work my way around the hole, overlapping each piece as I go. I went all the way around twice, just to be safe.

Specially rated foil tape. It's expensive, but one roll will last you forever.

Start overlapping the small strips.

I went all the way around twice.

Mounting the Tower

Next, I sanity check to make sure that everything lines up. I put the tower on top, drop the bolts through, and in general just make sure everything fits. This time, I had to adjust one of the bolt holes, as I hadn't drilled it straight down. No biggie.

It all fits!

This is optional, but you may want to put a piece of acrylic or some such inside the fridge to help hold the bolts. In my case, the plastic on the inside was a little irregular, and I worried that if I tightened the bolts down too much, I might crack the plastic inside. This piece of acrylic allowed me to spread the load out over a larger, more regular area.

Small piece of acrylic to hold the bolts on the inside.

Once everything was in place, I tightened down the bolts all the way. This tower isn't going anywhere.

Mounting the Distributor

In order to send gas to both kegs, we need to incorporate a distributor (AKA manifold). Again, we have to be careful where we drill. I wanted the distributor in a place where it would be easy to get the gas to the inlet from the regulator on the cylinder, and also where I could still mess with the swivel nuts on the outlet. I chose to mount it on the left side of the fridge, up in the corner. Make sure that wherever you put it, you can still operate the shutoff valves. On my last build I put it in the back right corner, with the outlets facing forward. For various reasons that wouldn't quite work with this fridge, so I went with this other option. I repeated the "door open, fridge on" test to make sure I wouldn't hit any cooling lines, and drilled two small holes, carefully measured using the distributor as a template on the top of the fridge, and measuring from known points inside the fridge (the bolts for the tower). Cranked it down and the manifold is mounted.

Looking up at the distributor from inside the fridge. Yes, I'm lying with my head in the fridge to take this picture.

All cozy up in the corner. Enough room to operate the rear shutoff valve thanks to the little cutout in the cooling plate.

Everything in its right place.

It's not shown here, but my fridge had a plastic top that went over the metal top. I drilled a 3" hole through this and lowered it over the tower. This hides all the bolts (both from the tower and the manifold) which is kind of neat. Not necessary, but a nice touch.

Tower Cooling

One problem people with kegerators sometimes run into is the lines near the faucets becoming significantly warmer than the beer inside the fridge. This can cause the first pour to be very foamy, as the solubility of CO₂ decreases with temperature. Some people like to rig up a contraption to blow cold air up into the tower, but this is troublesome for two reasons. First, you have to find power for the fan, which often involves running a power cord out through the drain spout in the fridge (and then finding a plug for it, or wiring it into the fridge's power supply). Second, you have to worry about the fan crapping out at some later date (operating inside the humid, cold fridge) and then replacing it. I prefer a more passive solution. I use some lengths of 1/2" copper pipe to conduct heat away from the tower (and the beer lines).

Because I drilled a full 3" hole in the top of the fridge, I need something to help hold the copper pipe and the insulation up. So I used my hole saw to drill a 3" puck of styrofoam from some scrap I had lying around. I wrapped some of the foil tape around the edges to keep the styrofoam from crumbling off.

It's so cute!

All wrapped up.

Next, I drilled two holes in the styrofoam with a 9/16" spade bit to hold the 1/2" copper pipe (which is actually slightly more than 1/2" in diameter). I then cut two equal lengths of copper pipe, just long enough to go from a few inches below the shanks to a few inches into the fridge.

Drilling holes for the pipe.

Pipe cutter. Easy peasy.

They fit!

I then cut two shorter lengths of copper pipe and procured two 1/2" copper tees from my local hardware store. I sweated them together (silver solder). No need to worry about being watertight, I just didn't want them coming apart. In retrospect, this was probably a bad idea, and will make removing the tower much more involved in the future, if required. I'm counting on not ever having to do that. If you can get the copper to stay together without soldering, do that instead.

Silver soldered together.

Now for the fun part. I got some insulating spray foam, which I used to both hold the styrofoam "puck" in place, and to insulate the tower further (it came with a thin foam sheet, but I wanted moar!). This stuff expands really quickly, so spraying down into the tower wound up creating a big air space at the bottom of the tower. I remedied this by drilling a small hole in the puck once it was secure, and inserting the straw from the spray foam up and filling in the gap from below. Worked nicely and automatically filled the hole I drilled, to boot! Be careful with the spray foam, it is very easy to overdo it. It expands a LOT. The copper pipe is heavy, so to keep it in place while the foam cured, I ran some twine through it, tied it up at the top and suspended it from a piece of silverware. Resourceful, I know.

Spray foam. Be careful with this stuff, it expands like crazy and sticks to everything. Wear gloves. Have lots of rags handy.

Holding the "puck" in place.

Holding up the pipe while the foam cures.

Assembling the Gas Lines

While the foam cured, I decided to assemble the gas lines. I already had some 5/16" gas hose lying around (bought in bulk from MicroMatic a few years ago), along with some adjustable worm clamps that I always like to have lying around for various hose-fitting needs. The gas lines are easy, but if you have trouble getting them over the barb for the swivel nut, I suggest putting the swivel nut on a disconnect, so it doesn't slip out, and soaking the end of the hose in boiling water for a minute or so to soften it. Don't forget to put the worm clamp on before you put the hose over the barb. I push the hose up to the end of the barbed part of the barb (if you go all the way, there's no room for the swivel nut to loosen). Then tighten the clamp down, but not too tight. You don't want to destroy the hose.

Using the disconnect to help hold the barb steady.

Gas lines for the kegs done.

I attached the lines to the distributor, along with another line to take gas from the regulator to the distributor. Make sure you have the lengths right before you cut. You may have to take into account a circuitous path if the kegs don't leave you much room. On the other hand, you don't want the lines too long, because then you may run out of room and things become a tangled mess. Don't forget to use flared nylon washers anywhere you're trying to connect metal to metal with flared fittings. They're cheap and they stop leaks. I bought 100 or so on eBay a few years ago and haven't looked back. They are not cost-effective to buy individually from homebrew retailers.

All gas lines attached.

Assembling the Tower

The last step is to re-assemble the tower. Now that the foam has cured, things look pretty good, and the copper pipe is holding in place on its own. I removed the ball lock disconnects from the liquid lines because I wasn't going to be able to thread the swivel nuts through the copper pipe (the 3/16" ID beer tubing just barely fits). Removing the included Oetiker clamps is a pain, but can be done with the right tools. I used a wire cutter to get underneath the lip and then pry the clamps off. I then dropped the beer line through the shank-mounting hardware and down through the copper pipes. Tightening the shanks in such a cramped space can be pretty difficult. Be patient, don't be afraid to just turn a small amount at a time. Once the shanks are mounted you can put the faucets on. Make sure you have a faucet wrench. They are cheap and will allow you to tighten your faucets without scratching them all up. The final step is to re-attach the liquid disconnects. You can repeat the process from attaching the gas disconnects above, but you will likely need the boiling water this time, as getting the 3/16" ID beverage tube over the 1/4" hose barbs is tricky otherwise.

Foam all dried!

Shanks mounted.

Faucets mounted.

Liquid disconnects attached.

Some folks recommend having special gas diffusers inside the keg for nitro dispensing. I'm going to see how well it works without. I assume it will take longer to carbonate/nitrogenate, but I really have no baseline here. With CO₂, I use the "set it and forget it" method. I plan to use the same here and see how it goes.

Conclusion

This project really did not take long at all. I credit some of that with my previous experience, but all in all, it is not a very laborious project. It took me maybe 4-5 hours, spread over an evening and a brew day. Now all I can do is wait for my dry Irish stout to finish. I'm contemplating brewing up another batch of Speckled Heifer and seeing what the nitro does to it. I'll make sure to post some pictures and tasting notes!