The Mother of All Fermentation Chillers

I have a passion, a "sickness", my wife calls it. I love beer - and I love to make it. I have been homebrewing beer for about 11 years - ever since my friend, Ross, showed me how to do it on his stove back in South Carolina. It is the perfect hobby.

There is fabrication, science, cooking, and the best part, consumption of the final product! I started brewing on the Connecticut coast, where the weather is very mild throughout the year. Sure, it gets cold in the winter or hot in the summer, but the extremes are not that bad for that long. Then I moved to the Southwest...

The Problem with Summertime

In Arizona we are blessed with 300+ days of sunshine. We are also "blessed" with 90F+ degree tap water in the summer and 110F+ degrees outside. In order to not go broke, my house has setback thermostats that keep the temp at 78 while we are away during the day, and 75 when we are there. The wet t-shirt trick works like a charm - except in the summer. Because it is so dry I can usually get about 10 degrees off of the ambient. Still, I much prefer to use my chest freezer with a temp control to keep fermentation consistent. The "problem" is it is usually filled with full kegs at lagering or serving temps.

Using the Freezer I Have Instead of Buying Another One

I had to have a better plan for fermentation. I looked at designs such as the Son of a Fermentation Chiller, and the 38DD version, but I didn't feel like messing with ice jugs daily. A second chest freezer was out of the question - I just don't have that kind of space. I have also seen people put partitions in their freezer or put a Fermwrap on the carboy inside the freezer. The thought of having the freezer and the heater fight to the death while I line the pockets of the electric company gave me chills (pun intended). Then it hit me. The chest freezer is so efficient because the cold air sinks. There is not much loss when you open the top. I needed to design something that took advantage of the laws of thermodynamics - cool air sinks, and warmer air rises. Thus was born the Mother...

The Design

Since this thing was going to be permanent I had to figure out a way to get to the bottom kegs. I designed the floor of the unit to have two trapdoors and a removable center support. Access to the ferm chamber is from the front. The unit has a dedicated temp control to keep the freezer at serving temps and another one to control the fans for the fermentation. The top unit has two 120mm fans to circulate the cold air. To improve cooling efficiency, I added two 4" X 24" ABS pipes as intake and exhaust tubes. The cold air intake goes down into the freezer. I cut it so that it stops 1" short of the compressor shelf. The hot air exhaust sticks up inside the fermentation chamber and returns the warmest air back down into the freezer.

Construction Details

The ports were constructed by first adding a flange to the ends of the two pipes. I glued a coupler to the pipe then cut it almost entirely off on a table saw leaving a lip to fit a routed groove.

The entire box is constructed of birch plywood that I found at the local Home Depot. What would be the collar on a normal chest freezer mod is made out of 2 X 4s. Each corner is strengthened with 2 X 2s. Insulation is two layers of 3/4" rigid foam insulation - "extruded" polystyrene, not "expanded" (a.k.a. coffee cups). The top and middle is wrapped with some 1 X 4" poplar stained with red oak stain. At some point I intend to finish the wood with some satin polyurethane. I have room for 6 taps on the left hand side spaced 3" on center. An 18" drip tray will also be added later.

The Mother Put to Use

My 14.8 CF freezer can hold six kegs comfortably (eight if I squeeze them in "8o8o8" configuration). The Mother will hold (4) 6.5 carboys comfortably up top. As for the gas plumbing - the initial plan is to run with two secondary regulators (one for "normal" beers, and one for belgians and hefe's). One regulator will be hooked up to a 4 way manifold and the other a 2 way manifold. I also intend to have a mechanism for counter pressure filling outside the unit, or purging kegs prior to transfer.

As of this writing I still have not fermented in there as I have been called away on business and leisure travel (Ed: "called away" on leisure travel. How nice, Mylo!). However, I did do a test of the cooling capacity. It is entirely possible to ferment lagers up top. However, I'll probably refrain from lagers at least until the temps return to the 70's in my Arizona garage.

Brew Strong!

MyloFiore is an avid homebrewer and lives in Scottsdale, AZ with his ever-enduring wife, Nancy, pre-teen son & daughter and Yorkie, Winston. He can often be found raising hell on the Brewing Network's forum. If he were a beer he would be a Saison.

Baron Ken on 08/07/08 03:49 pm writes
Perhaps add a wall so that you could ferment lagers and ales at same time. Would require additional port tubes, fans and controller for the "extra" chamber.

Great work!
MyloFiore on 08/09/08 01:45 pm writes
That is definitely a good "upgrade" suggestion, and would probably still be very efficient! The cold air from the freezer comes in on the left. All I would need is a removable, insulated panel with a fan on it attached to another controller. Left side for lagers, right side for ales. Thanks for the tip!

baltobrewer on 08/11/08 05:04 pm writes
Great job, man....way to ferment strong! You've got some mad cabinetmaking skills too... One did you secure it to the chest freezer itself? Does it lip over or did you use some kind of adhesive?
MyloFiore on 08/16/08 03:39 pm writes
Yes, Jay. The red-oak stained collar lips over the freezer's edge - just about 3/4". I used some 1" wide, dense weatherstripping to make a tight seal - but otherwise it's just held on with gravity. I'm not worried about it going anywhere. It probably weighs 100 lbs or so. I guess I finally put my BFA in furniture-making to good use! ;-) A tablesaw makes the job real easy. However, there is enough trim work in the design to hide any raggedy edges - so I'm sure anybody could do it with a carefully guided circular saw. CAD drawings, forecoming.

Uhrigbrauer on 08/24/08 05:40 pm writes
Super, duper, awesomeness-maximus! I though of doing something similar.. thanks for putting in the hard work so I can copy it!

GnomeSherpa on 09/09/08 01:14 am writes
That is awesome. Looks like I've got a new project for the brewhouse. Thanks for the great idea.
mmadia on 09/09/08 07:12 pm writes
Great build!

Would it be better to have the cold tube also extend to the top of the fermentation chamber? This should allow the cold air to settle to the bottom of the fermentation chamber, instead of the bottom of the chest freezer.
MyloFiore on 10/08/08 12:03 pm writes
Actually the fan that pulls into the top has the tube down to the bottom to draw the coldest air. The hot air return tube extends to the top of the ferm chamber, and the fan on it blows back into the freezer - drawing the warmest air back down.
SmokeEater on 02/19/09 09:29 am writes
Any updates? You use it yet? Plans?
Chris on 03/25/10 10:09 am writes
Any updates? How is the system working? Can you ferment lagers? How often is the compressor going on?

What would you do differently?

Jon on 06/08/10 12:37 pm writes
Love this!! Great Job, I know what I'll be Building soon!!?? Any updates? What would you do differently?
MyloFiore on 06/08/10 01:36 pm writes
I had thought about providing plans, but I am not sure of what value they would be, unless you used the same size chest freezer as I did. Hopefully you can get the general idea of the design from the pictures, and size it according to your freezer.

I have used it faithfully for almost two years now. I do lagers in the winter, and ales all year long - just because it's in my 95+ degree garage in summer, and I don't want to line the pockets of my electric company (any more than I do!).

Sometimes I'm a little miffed that I can't rack directly from the inside, but that would mean that I would have to make it at least 6-8 inches higher to accomodate my long SS racking cane. The added cost didn't outweigh the benefit, however, as the dimensions were the largest that I could get without buying another sheet of plywood, insulation, and longer frame pieces... It probably would have translated into another $150 when all was said and done.

The only other thing that I might have done differently (and I can still do) is to eliminate the "intake" tube altogether. It seemed like a good idea at the time to drap the coldest air from as low as I could get it. In reality, it's in the way of the last tap. The fans are running at the max, which is something silly like 1200CF/min so I don't think it would make a bit of difference, anyway.

Good luck with the build, Jon. Let me know how it goes!

Jamie Iomo on 12/17/10 02:45 pm writes

Awesome blog, great write up, thank you!
Fisher kel Tath on 01/21/11 10:53 pm writes
What is the wiring and electronics like? also do you have problems with moisture and getting too cold?

moeman on 01/29/11 03:17 pm writes
This is great. I want one bad.


1) How does this thing stay aligned on the freezer? I realize it is held down just by gravity, but does any part of it actually fit down into the chest to prevent it from being pushed horizontally?

2) Electronics!! What kind of fans are you useing? What is the wiring like in there? Do you need a fan on both tubes, or would one be enough?

3) cabinet making question: How do the doors close nicely and stay closed?

prudent1 on 04/11/11 05:48 am writes
This is a real nice idea-thanks for the posting. If you want to rack from it couldn't you just put a hatch on top? just an idea...
MyloFiore on 09/21/11 10:47 am writes
@Fisher - I am in the AZ desert - so moisture isn't that big of a problem - but I still do get some in summertime. Others have recommended "damp-rid" or a few shop towels to pull out the moisture.

@moeman -

ALIGNMENT: I have a decorative piece of molding that extends down and wraps the top edge of the freezer by an inch or so. It's quite heavy, though, so even without it I don't think it would slide off.

ELECTRONICS: I use two 120mm computer fans. One would probably do fine, but two is much more efficient. They are powered by a hacked laptop transfomer. I currently use two Rancos. One is two stage (so I can heat the top in winter if needed), and the other is single stage for serving. The Ranco's have their own relays that essentially cut the power to either the compressor, or the fans. I also have an additional DPDT relay that is wired in there so that when I open the doors, the light comes on, and the fans go off. Not required, but a nice user friendly feature. I am strongly considering swapping out the Rancos with a FermTroller(BrewTroller) system. The Ranco units are great, but they do not have any short cycle protection or logging capability.

CABINETRY: I used some of those roller clasps to keep the doors closed tightly. I assume that the magnetic catches would also work fine.

@prudent1 - Great suggestion. I currently use the to store carboys, but a hatch would also make racking much easier.
Martin on 01/16/12 07:18 am writes
Maybe i'm stupid, but how does this work? I understand that you are pulling the cool air from the freezer(?), but how? Did you drill a hole in it's lid? :)
Push Eject on 01/16/12 07:47 am writes
The freezer's lid has been removed.
zorch on 05/23/12 08:03 am writes
Not having much cabinet making experience (I took band rather than woodshop...), I am curious whether having a solid top is critical to the structure?

I was thinking that it might be handy to install the original freezer lid on the top of the new chamber, rather than throw it away or have it take up space. It's already insulated and the correct size. Also, being able to open the top would allow me to use a chain lift or block and tackle to assist me (and save my back) when lifting heavy carboys out of the bottom chamber.

Mylo on 06/14/12 03:17 pm writes
@zorch -

Sounds like an interesting idea. FYI, the TOP chamber is where the fermenters are. Heat rises, etc... I use the bottom for serving - though I suppose you can use the system for fermenting two different temperatures, such as lagers on the bottom, and ales up top.

Anyway, to answer your question... No a solid top is not necessary, however, you would need small, triangular braces in the four top corners to keep the box square.
Rev Joe on 07/04/12 10:37 pm writes
I really like this set up. I am in ABQ, NM so I am thinking of going this route. How big is your freezer? I thought you gave te size but did not see it when I re-read this. My wife ight think I am nuts buying a freezer but hey she seems ok with the fact that I might put a shed/brewhouse pub out back, this is would be the logical next step.
Push Eject on 07/05/12 07:31 am writes
Joe, thanks for for the comment. Mylo's freezer is 14.8 cubic feet.

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