DIY Fermentation Chamber

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Ask almost any intermediate homebrewer what single change you can make to brew better beer and they'll all say the same thing: Fermentation Temperature Control. After employing proper sanitization practices and pitching healthy yeast, stable temperature control of your fermenting beer is the next big step towards award winning brews.
There are many options when it comes to leveraging some control over fermentation temps. A water bath with frozen water bottles in the summer and warm blankets in the winter can go a decent way towards stabilizing your temps when the weather is at its extremes. But to really dial in on proper temps, you need to bring your fermentation into the 21st century

Enter the Fermentation Chamber

A fermentation chamber is simply an insulated box with internal heating/cooling elements that can react to small changes in monitored beer temperatures, correcting small deviations from your desired fermentation temperature without large temperature swings. The result is extremely fine-tuned temperature control and better homebrew. In this article, we're going to learn how to build a fermentation chamber using an old mini fridge.
There are pros and cons to this approach. First, depending on how big you make your chamber, a mini fridge may have trouble keeping your beers cool during the warmer months. Second, unless you are diligent in sealing your chamber, a side loading setup will be more prone to cold air loss than a chest style chamber made out of a freezer. I'm not one to shy away from a challenge though, so for this article we'll be building a large, side loading fermentation chamber.
Material Needed:
Old (or new) mini-fridge/dorm fridge
7/16” thick 4'x8' OSB*
1” thick 4'x8' Rigid Foam Sheets*
2x4 lumber*
Aluminum Tape
Foam Tape
(Optional) Casters
#8 or #10 x 2.5” screws
Temp Controller Software (see step 9 for options)
Tools Needed:
Table Saw or Circular Saw for OSB
Utility Knife for Foam Insulation
*Note: The quantities of lumber needed will depend on how big your fridge is, and how many fermenters you want to accommodate. Whatever external area you determine your chamber to be, you'll need at least that much OSB, and nearly double that in rigid foam insulation.

Step 1: Fridge Prep

Remove the door from your mini fridge. We will be building an extension to make the cool area of the fridge larger, and we want a clean seal between the extension and the fridge. Removing the door will make adding the extension much easier.
We want to start with a clean mini-fridge with the door removed. The further along we get in the build process, the more difficult access to the fridge's internals will be, so get out your scrubbing gear and make the fridge shines inside and out. We don't want any old mold floating around in the chamber.

Step 2: Build the Base

Here's where your first customization comes in. You want the depth of your base to be the same width as your fridge. How long you make it will depend on how many fermenters you want to accommodate at any one time. Remember, this is also where the power of your fridge will come into play. A smaller temperature controlled area will be easier to regulate than a big area, but the tradeoff is less room for fermenters! So take a moment and think realistically about how many beers you can see yourself fermenting at the same time that also share similar temperature needs. I have enough room in mine for 5 fermenters, and in retrospect this is a little too large. I've maxed out at 3 fermenters at one time, and my old fridge cycles constantly to keep up with demand during the summer.
2x4 Frame for the base
Although the pictures attached show me adding wheels at this point, I found the wheels made it more difficult to attach the top and bottom frames. I'd suggest waiting until the top and bottom are attached, then add casters later.
Cut a piece of OSB to match the dimensions of your 2x4 frame, and screw it down.
Completed base. Best to wait to add the wheels until a later step

Step 3: Build the Top and Attach to Base

If you're following along with my design, you will want the interior dimensions of the top frame to be 3” wider and longer than the base. This allows room for us to attach the vertical supports that will provide a tight fit for the fridge. Measure your fridge height and make your supports tall enough so they reach the bottom of your base frame, and the top of your top frame. In the image below I attached the supports to the underside of the top first, and then flipped the entire top/support combo so I could attach it to base.
Attaching the supports to the underside of the top
Before attaching the supports to the top/base, you need to get your fridge positioned where you want it on the base. Make sure the rear of the fridge is flush with the end of your base and the power cord is accessible from outside the chamber.
Once positioned, attach the supports flush to the top of the upper frame and to the bottom of the base. For this step you will want to use #8x2.5” or #10x2.5” screws to attach the support bars to the frames. When attaching the back-side supports, just space them evenly along the span of your chamber. When attaching the front supports, you need to keep in mind that two of the supports will be used as your door frame. Mine turned out to work fine when evenly spaced, but depending on your final size, you may need to make a larger/smaller opening for the door and space your supports to get the size you want.
Now we have the top and bottom attached via the support arms, with the fridge fit snugly between the supports
This is also where you can decide whether or not you want to add wheels. I've already relocated my chamber a couple of times, so it was a worthwhile addition for me. Remember to get enough casters of the proper size to handle your weight. 5 gallons of beer will weigh roughly 40 pounds, plus the weight of the structure and fridge. Plan accordingly, and remember it's better to have more support than you need than not enough.
At this point, you should have a big rectangular structure with a fridge placed at one end and a sheathed top and bottom.
Here's a view of the fridge positioned between the top and bottom

Step 4: Sheathing the Backside

Now we want to start adding OSB. Measure the area of the backside of your chamber, from the bottom of your top frame, and the bottom of your base. We want full coverage here, as the sheathing will also allow us to mount insulating foam sheets in a later step. Wherever possible we want to use complete insulation sheets, as this reduces the possibility of air leaks. As you add sheathing, go ahead and add insulation as well. It's much easier to get big sheets of insulation in place when the structure is more open, rather than waiting until it's nearly enclosed. If you use similar rigid insulation like I have, it is pretty easy to cut with a box cutter and snap into precise pieces.
7/16” OSB added to the back of the chamber

Step 5: Insulating the Back, Floor, and Ceiling

Although the pictures don't show it, you will want to add insulation in between the support structures as well as in front of them. When completed, you'll have double-thick foam insulation on most of the wall, save where the supports run from top to bottom. As you add insulating sheets, use aluminum tape to seal all edges and gaps between foam/foam and foam/wood. This is an important step; the more precaution you take here, the more efficient your chamber will heat/cool your beer. When you are finished, you should have insulation on the floor, ceiling, and back wall of the chamber. Build up enough insulation at the floor and ceiling to match the dimensions of your fridge. If you leave a gap at the top/bottom of your fridge, you'll be cooling an area that will never be used for beer. The idea is that the fridge internals are only open to the area where beer will sit, and nowhere else.
Insulation on the floor and back wall. Not shown is the insulation on the interior ceiling, and the second sheet of insulation I eventually added to meet the bottom edge of the fridge

Step 6: Sheathing/Insulating the End Opposite the Fridge

Only after you complete insulating the floor, ceiling, and back wall should you enclose the end of the chamber opposite the fridge. As before, sheath the outside with a piece of OSB, and then use rigid foam insulation both between and on top of the supports. When finished, seal all openings with aluminum tape. We will leave the end of the chamber with the fridge completely open to aid in heat dissipation. Do not enclose the fridge entirely. Not only will it ruin any chance of cooling efficiently, it also poses a fire hazard.

Step 7: All Remaining Insulation

Insulate the gap between your door support and the fridge, running the insulation part-way down the side of the fridge as shown
At this point, you should have everything done except the front. If your structure is similar to mine, you'll have a big door (between the first two supports), and then a gap between a support and the start of the fridge. We want to add insulation here before installing sheathing. This is backwards from what you've done for the previous steps. Don't cover the entire fridge with insulation, as some mini*fridges use the sides as heat dissipation. Leaving it uninsulated will let that heat escape towards the rear opening we left for the fridge.
Now you can add a piece of sheathing that covers the entire front except where the door goes. You want to leave roughly half the width of the door frame un-sheathed so you have room for the door hinges.
Be sure to leave a portion of the door frame support uncovered so you have room for the door to sit against the support, and for the hinges to swing properly

Step 8: Make the Door

Measure the opening of unsheathed area where your door will go. Subtract roughly 1/2” from that dimension so your door will fit into the opening with room for the hinges to operate. Depending on which hinges you select, that 1/2” dimension may need to be a little bigger. You can test this by placing your hinges against the area you just sheathed and operating the hinge to get an idea of clearances. You don't want to cut too much off, because we still want a well-sealed door. Test fit your door once its cut, and once you're happy, install the door using two hinges and two barrel-bolt locks.
Door installed with hinges and barrel bolt locks
Once the door is installed and working properly, add some foam tape around where the door touches the frame when it closes. This will make closing the door slightly harder, but will ensure most of the air gaps between the door and its frame are sealed well.
Foam tape goes a long way to sealing an otherwise drafty door
The last step for the door is to add insulation to the interior. I had my wife close me inside the chamber so I could mark the appropriate area with a sharpie, and then cut the foam to match. If your chamber is too small to climb into, or you don't have someone on the outside to make sure you don't get locked in, then a rough estimate here will be good enough.
Insulating the door is the last step in making your chamber as efficient as possible
And now we have a complete chamber! The only thing left to do is add some smarts to it so you have completely automated temperature control.

Step 9: Temp Control Options

I won't go into a lot of detail for this step, because there are tons of configurations out there to accomplish temperature control of your new fermentation chamber. I opted to go with a homemade BrewPi controller, and I followed the excellent thread created by HomeBrewTalk user FuzzeWuzze here Following his steps, with a little electronics work you can have a pretty impressive and capable automation system that will follow your fermentation temperature profile precisely. You can even add a small heater to the interior of your chamber to keep your temps up in the cold of winter. Most electronic options here will require drilling a small hole in the rear of your chamber, through both sheathing and foam, to get wires and temp probes inside the chamber. Just be sure to tape around the hole to minimize loss of efficiency.
Alternatively, if you don't want or need the level of detail provided by the BrewPi Controller, you can always use an STC1000 to build a simple on/off controller that reacts to the temperature of your wort. HomeBrewTalk user goldenislesbrewsupply has an excellent thread for wiring up the controller here
In the end, you should have a better means of keeping your fermentation under control. And the workbench tops makes a great surface for racking beers and storing equipment.
All Done!
If you enjoyed this article, check out more cool projects for home brewing and beyond at http://www.castleseven.net Happy Brewing!
Interesting, I never thought of building out a chamber to extend a side door mini-fridge into a full usable chamber. In your experience what is the overall cooling efficiency like? Does the fridge run longer to maintain temps in the increased interior space? I'm curious how a compressor rated for a small fridge maintains a consistent temp in a larger chamber without running non-stop.
For those that run fermentation chambers, do you keep it running all the time? I brew once or twice a month and have been thinking about doing a ferm chamber. I know if you brew a lot it makes sense to always run it, but what if you do not. The other side is it may run longer if it is always on compared to only running it when you need it, similar to how computer equipment can be.
I'm not 100% on this, but I believe it can handle more cubic feet because you're not typically asking it to run at 35F or what have you unless you're doing lagers. So it's more work but less work in that sense. But I'm not a thermo-engineer (is that a thing).
Do you ever have condensation problems? I would think that any persistent condensation might cause rot or mold especially in the wood framing. If this is a problem, some marine paint and caulking might be a solution.
No need to run it when it's not in use. As the OP mentioned, I use an STC1000 to control the temp in mine. When it's done fermenting, I shut it down until the next batch.
This is kind of a question of what fits your needs. Is your chamber cooling mostly or heating mostly? How big is it and how long does it take to get just the air in the box down to your target temp? Are you using it to drop those last few degrees to pitching temp or is you wort already there before it goes in the chamber?
In my application my basement is about 53-55f in 6 months out of the year so if the chamber is not in use, it is off. In summer when it is 72f, I click it on the day before and set it for about 5 degrees or more below my intended pitching temp because I stop chilling my wort at about 70f and let the chamber drop it to 63-65f before I pitch.
Someone who has their chamber in a garage in Houston in July might benefit from leaving it on all summer just to keep the condensation down and because it might take more than a day to get it down to temp in the first place.
I will never use a chest freezer for fermentation chamber just because of the lift-over height. I also would not do this design with a single door because of the difficulty of getting the first fermentor toward the back.
Point is, we all have different approaches and needs. I use an old 1955 GE flattop fridge because I had it, the floor is plenty strong and it will fit three of a specific shape 7 gallon bucket ferment if needed. Some day it will be a multi-chamber cool room powered by a window AC...and not many people would find that simple.
If you buy the programmable version of the STC1000, it can be flashed with new firmware that will also provide precise control over a fermentation profile. An Arduino is required reprogram the controller but it is fairly easy to do. Options and details are available here https://github.com/matsstaff/stc1000p. Note the author provides an online tool to preconfigure profiles prior to downloading the firmware which allows the user to customize the firmware prior to installing in the STC1000. This is easier than scrolling through and setting parameters after the firmware is installed if the user already knows the profiles they need. The firmware accommodates up to 6 different profiles.
I've seen some nice prebuilt units available online as well with an integral Arduino for uploading the firmware as it evolves. Brulosophy has a good write-up about their experience with the Black Box controller.
Good point. I'd probably have to install a lift in a chest freezer. I have a brick area that is my chamber. It holds a constant temp being in the basement and surrounded by brick. Haven't quite figured out how to use it in the heat of summer besides brewing belgians.
this looks great.
I currently use a fridge which at a push can fit 2 FV vertically.
Horizontal fitting would be very useful, in this type of design, and could offer a more consistent temperature I think.
I get up to 3 Deg C temp swing between the top and bottom fermenter.
The fridge I have is quite long/large, so could work as this type of setup (I could actually get 4 fermenters in if this is the case, but a smaller fridge would work just fine.
True. I used to have mine out in my shop which is non-insulated metal building.
Inside the shop, the temperature gets well over triple digits during the summer time (Atlanta). My mini-fridge used to run most of the day trying to keep up. So I moved it into my garage which is a much more moderate 80 degree (high) inside the garage. Now the mini fridge is much happier and runs much less.
I built something similar to this recently and used thin plastex wall siding to line the inside. Easy to clean, waterproof (if caulked at the seams), and cheap. Also used the dual relay inkbird temp controller and placed a heater inside (and connected to controller) as well as a fan to circulate air. Whole thing works great.
i live in southern california and have to use mine year round just to get happy ale fermentation temperatures. even in the summer when I was living in an old house with awful insulation, my fermentation chamber rarely ran. it is an old chest freezer hooked up with and STC 1000. it holds everything cold very well and is "on" all the time in the sense that it can turn on whenever it needs. i do not turn it off manually ever. with the STC 1000, it is being controlled by the computer so the computer turns it on when it needs to and off when it doesn't. there is also a built in feature to protect the compressor that won't allow the fridge to turn back on unless a certain amount of time has passed.
Have you had any issues with the foam being too "sticky," especially on the bottom, while trying to get things in and out? It would seem that perhaps a layer of plexiglass or some other smooth material would be a nice addition, especially on the floor of the chamber. I also always worry about spills and such, and having a more smooth/cleanable interior would be desirable.
Regarding Step 8...it's nice to see a relationship strong enough where you can trust your wife enough to shut you up in a box, and then let you out again!!! :p
Looks good but there is one issue that I notice with this system. Most modern refrigerators have their heat exchanger in the side and top walls. Having the entire refrigerator inside a box will mix the cold air with the exchanged heat radiated from the walls. It is why window air conditioners need to be in the window so the y can vent the heat.
Ideal design would have the box stop at the dorm fridge doorway, acting as a collar, rather than a coffin.
I also noticed the foam insulation on the side of the fridge. This will block the heat exchange and most likely lower the cooling capacity and more than likely cause premature death. From a safety standpoint I would be concerned of excess heat buildup on the sides. Not to mention the concern of mixing the exchanged heat into the cooling environment is akin to peeing into the wind.
Hate to be a Debbie Downer" but it is a real issue
I've done both, and I think I followed this build from another site, mine was a top loader. Im not a carpenter by any stretch of the imagination, it did work but ran constantly in the summer. The compressor on the fridge eventually crapped out and I went to Craig's list and bough an decent chest freezer for 80.00 and it works like a champ in all types of weather, I live in the Midwest with hot summers and cold winters and ive never had an issue with temp with the freezer. The original build ended up costing about 160.00 and took about 8 hours to complete and was inefficient. Chest freezer was about 100.00 and took under an hour to set up. If your up for a challenge and have better carpentry skill then me do the build otherwise save yourself time and money and just go with a chest freezer.
Seems a bit big and difficult to use the space consumed by the huge and heavy device. This is what I did...
It gets the job done in less than 1/3 the space, and no problem with blocked heat exchangers.
Nice build!!
I like your approach & concept.... If I want to ferment more than one carboy chances are it would be a week apart and the temp schedule would not match the previous beer anyway... By that time my first beer is in a diastole rest. For more capacity I would build 2 of your style so I can control multiple beers individually
I received a temp chamber similar to this, almost free, from someone moving up to a glycol chiller. I definitely appreciate it, but I'd add the following "lessons learned":

1) make sure the fermentation vessel area is tall enough to fit carboys/buckets WITH airlocks (I had to cut off my S-airlocks short, to fit at all)

2) add internal plugs for the temperature probe (1/8" RCA jack), and the fan (120V plug). and the heater (120V) are not 100% hard-wired. I modified it to add those, so I can switch easily between a ferm-wrap, or a space heater, or whatever, depending on my needs
Pretty much what I was going to say. The custom ferm chamber is cool, and probably a better idea where space is at a premium (as in, you can build it to fit the space you have) but a s/h freezer is going to be a lot cheaper, easier, and probably more efficient. You don't get to show off your DIY chops I spose, and that's definitely a factor. If I was to make this, it'd be under a work bench, with removable hinge pins for better access. That'd be nice.
I have a regular fridge, it fits two 8 gal fermenters, and is a lot easier to clean up than the above ferm chamber should some catastrophe ensue. Even with a pretty average seal I'm thinking it still leaks less energy than the ferm chamber... plus you can score one for free 99% of the time
I built one similar with a smaller mini-fridge (square size) using 2 inch foam and I couldn't get it to get cold (below 60F) even with big fan on the coils. Make sure you use the bigger mini-fridge shown or you will probably not be satisfied with your units performance. The story ends OK though - I turned the cabinet into a roll around mini- bar for the patio.
I've got almost no carpentry skills (working on getting better!) and I did my ferm chamber with a wine fridge and a Johnson controller. Zero carpentry experience needed - one drill through the bottom of the insulation to feed the temperature probe, some velcro to hold the controller unit on the side/back and I have a fermentation chamber that can do lagering (as long as I don't need to get colder than 45F, which I don't know many styles that do) for roughly $110. You can find wine fridges (which are typically a little more open than standard mini-fridges) on CL for $30ish.
I admittedly don't know much about thermodynamics but I'd think the article's box would also suffer from compressor burnout and hot/cold spots further away/closer to from the fridge. I also don't know when I would need to ferment multiple carboys at the same time, let alone at the same temperature.
That said, it's a pretty good looking box that you can paint up and hide from SWMBO!
When I get handy enough to build something like the article's, I plan to frame in my ferm chamber next to my keezer so it looks like a built in countertop. The missus hates that our converted detached garage look like a fridge discount store...
One question: What's the caster lb test needed for the frame and fridge?
What did you spend in materials? If I had to guess about $60-80. That would probably get you a pretty nice chest or upright freezer on CL; it would also get you 2/3 of the way towards a new 5cf chest freezer at Sears/Sam's/etc.
Lets also consider you are increasing the amount of space which the mini-fridge compressor needs to cool. Even if you didn't box it in like you did (kids don't try this at home); I can't imagine the manufacturer would over-design a compressor able to handle that load.
I dunno...seems like the penny wise, pound foolish approach.
That's what I would up doing after a lot of number crunching (lumber, rigid insulation, sealants at cheap) and trips to look at ragged out mini fridges....I just caught a Home Depot sale on a chest freezer....$160.00 and bought a controller $30.00. It is pretty much plug and play....and if you count your time as worth anything (I do) cheaper.
I do have an All-In-One vacuum wine pump and I just rack into or out of the chamber with minimal lifting involved.
So for less than 200 bucks, I was done. As a bonus, with temp controller, I can use unit as a spare fridge for the garden, beer cooler, for drying sausage, and even as an actual freezer! Plus I think the chest design is just more efficent than having a vertical door energy wise.
Not downing this build at all...if I had a mini fridge, I may gone that route.
I have 2 options. My big 14 cf chest freezer is normally my kegerator, which has an external temperature control. I also have a dead chest freezer that I have a PID controller controlling a small heating pad (50 watts or so) that I can use to raise the temperature above ambient in the winter, particularly handy for fermenting Belgians, or keeping beer warm while bottle conditioning. I also have a small upright fridge for use as my "Beer Fridge" when using my chest freezer as a lagering chamber.
Have you considered a fan in the fridge side to move the air and make it more consistent, cool other side faster?
I too was worried about how often the compressor would have to kick on and what kind of impact that would have on the lifetime of my fridge.
In the summer months it has to come on more often, but right now in my garage it's ~80 degrees and the fridge kicks on roughly once an hour for 5 - 10 minutes to keep my current beer at 68 degF.
The only place I notice any condensation is near the coils where the fridge has it's small "freezer" section. I added a cheap Eva-dry renewable mini dehumidifier and just make sure I towel out the fridge when I swap beers. No other issues so far.
Hahah, yea, it got really hot really fast inside, if she didn't let me out we'd have a problem for sure.
I haven't had any issues with the foam being sticky. It does take some finesse to get a bucket out (I can't just grate it along the surface of the foam without doing some damage, so a layer of plexi is a good idea.
The build detailed above works very well. I've had it running for over a year now, no issues whatsoever. I haven't pushed it to the limits but I've had 4 5-gallon batches in there at a time, and I've pushed the temp down to 52*F in the summer.
The heat exchanger portion of the fridge is left uncovered by insulation, so while other builds might be MORE efficient, this chamber does everything I want it to with the materials I had on hand.
Yep! I can't believe I left that out above. A small USB powered computer fan sits in the back of the fridge and helps to make temps more consistent.
Good effort but I think too many shortcomings.
Most have been addressed by other commentators so little need to repeat.
My (Muntons plastic bucket) fermentor, capacity 23 pints, is rather heavy & certainly would not be easy to place in either a chest or front load chamber.
BTW what did your wife charge to let you out?