Fermentation Chiller Systems and Findings


Until recently, if you wanted to homebrew lagers, you either needed a giant cave under your house, or you had an additional fridge/freezer of some sort, with a controller to switch the power on/off based on the beer temperature. For those that were used to “Throw it in a bucket in your basement and let the yeast work their magic!” a dedicated refrigerator may have been excess floor space and money they weren’t willing to spend.

There is a lot of info out there on how to make a fermentation chiller out of a fridge/freezer, but not much on the alternative systems. So I set out to evaluate them to see how they worked compared to each other. They come at different price points, have different capabilities/limitations, and require differing amounts of care-taking during fermentation.

Ice Pack Fermentation Chiller Systems

These systems are manual in nature. They consist of an insulated shell of some sort, and you regulate temperature by adding or removing ice packs. There’s no digital control temperature you set, you just monitor the temperature via whatever method you choose (temperature strip, separate thermometer, etc.) and adjust temperature by adding or taking away ice. This might give you the impression that the control is very crude, but physics steps up to make this actually work fairly slickly.

In Regards to Physics: when water is going through its phase change from solid ice to liquid, the physical conversion process acts as a sort of “thermal sponge” and uses any imbalance of temperature to suck up that heat, and use it to melt the ice rather than increase the temperature. As long as you’ve got ice in there to melt, the temperature stays fairly stable. And the temperature inside your insulated shell is controlled by how much ice you have in there. The more ice, the bigger the temperature drop below your room temperature.

Cool Brewing provides a guide with their insulated bag suggesting the use of empty 2L or 1L pop bottles filled with water and then frozen to make up your ice blocks. This has the convenience of allowing you to easily swap out a melted bottle, and replace it with a frozen bottle without having a giant puddle of water to mop up. It also provides a good regulation measure. For each 2L bottle of ice, you’ll get about 5˚F temperature drop, and for each 1L bottle, about 2.5˚F. And with the size of the 2L block of ice, it lasts a bit longer than 24 hours, so it makes it convenient if you have a regular maintenance time of day (every morning before work, just before going to bed, etc.) to change out the bottles without letting them lose their full cooling capacity.

Without electronics to control things, these systems are simple, which means they’re also the most affordable options out there. So you can get into lager fermentation without as much cash outlay. Cool Brewing makes a large, collapsible, zipper-close bag that fits fermentation buckets or carboys, with room to put multiple 2L bottles around them. FastFerment makes the same style bag customized to their unique conical fermenters. Brew Demon makes a “junior” version of these with a small neoprene jacket that slides over their fermenters with little pockets for small ice packs to slide into. With less insulation, and small ice pack size, it isn’t really practical for lager fermentation, but it does come in handy for runaway fermentations that heat up much faster than you want, and you need to get quick control.

The downside of these ice pack systems is the fact they require maintenance on a daily schedule. They are not a “set it and forget it” operation. It can become a bit tedious over a 2-3 week lager fermentation schedule to change out 2L bottles of water/ice every day and shuffle them to the freezer. And if you’ve got an out of town trip planned in the middle of that period, you can lose temperature control temporarily at some point.

But if you plan accordingly, these bags are simple and convenient lager fermentation options that won’t break the bank, or take up a lot of space when you’re finished fermenting (they all collapse and fold flat).

Cool Zone Brewing Modular Systems

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Gotta Brew offers a system that is a creative combination of common brewing hardware components, bundled together to create a system with a high level of control. You can customize your kit based on which of these components you may already have on hand. The unique bits are a flexible water cooling jacket, and an insulated bag to fit your fermenter into. It then plumbs into a standard temperature controller, submersible pump, and a 10-gallon cooler for the rest of the work.

The system is controlled by a temperature probe that slides down a sealed thermowell into the middle of your fermentation vessel. You wrap your fermenter (bucket, carboy, etc.) with the custom cooling jacket (which has a continuous water cooling channel weaving through it), and then lower this into the insulated bag, leaving the water inlet and outlet tubes sticking out. These get connected to the submersible pump, that you sit in the cooler full of ice water. The pump plugs into a standard Inkbird controller, that switches on/off based on the reading of the temperature probe. If the beer gets too warm, the pump kicks on and circulates cold water through the jacket until the temperature of your beer gets to the set point.

The upside of this system is that it allows very fine temperature control of your fermenting beer. The wrap-around jacket helps ensure even temperature throughout your whole batch. Utilizing a digital temperature controller allows you to dial in the temperature you want, and then just let the system work. The downside is the 10-gallon cooler still needs maintenance to ensure it’s always filled with ice/very cold water to ensure the system can control to the temperature you want. Unlike the ice pack fermenters, you do have the ability to really load up the cooler with ice, and buy yourself the opportunity to go away for a couple of days without your fermentation going out of control. But it does require some amount of regular ice change maintenance to avoid the disappointing discovery that you didn’t change it frequently enough, and now your 3 week temperature profile has an unplanned blip up…

Immersion Rod Chiller

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BrewJacket offers an electric heat exchanger system that makes use of a large metal rod that submerses into your fermenting beer to act as a heat conduit up to a chiller plate with a fan. The unit has a digital temperature set point controller, and the fan kicks on when above the set point to dissipate heat from the cooling fins. This effectively opens up a heat flow path up the immersion rod to channel heat out of your beer. The system controls to the temperature as read on a probe taped to the outside of your fermenter, and then the whole system sits in a giant thick insulated bag that’s kind of a cross between a bean bag and an overstuffed sleeping bag.

The limitation of this system is the rate it can cool your beer, if it needs to move several degrees. You may need to wait a bit longer to get your temperature down to the yeast pitch temperature you want. But once you hit that temperature, the immersion rod system does an exceptional job of keeping things under control and tight to your set temperature. The biggest plus of this system is it truly achieves the “set it and forget it” execution once you’ve achieved your target temperature. You leave it plugged in, and the fan will periodically kick on and off as needed, but you can go do other things for the next 2-3 weeks without having to babysit it.

Fermentation Vessel Considerations

If you’re making the move to do lager fermentation, you may want to consider a change to the type of fermenter you use. Typical fermenting buckets are made of HDPE plastic. Since lagering requires longer fermentation times, the opportunity for oxygen to pass through the walls of your fermenter, and oxygenate your beer increases. All of these fermentation chiller suppliers strongly recommend using PET bottles or glass carboys for lager fermentation rather than the typical HDPE Ale Pails. Based on oxygen permeability measurements, HDPE passes through roughly 50x as much oxygen as PET in a given amount of time. So there’s some science to back up these recommendations. Glass is an even better barrier, as it doesn’t allow any oxygen to pass through it. But if you don’t want the cost & weight of a glass carboy, PET is definitely a better fit to long fermentation times than your HDPE bucket.

Better Bottle is quite popular, and they come in a variety of sizes. They have ribs on them to give them strength and make them dent-resistant. But if you’ve ever used a carboy with a frothy fermentation, you’ll know how it can be a challenge to get down past the neck and get the walls clean. The Big Mouth Bubbler figured out how to take advantage of the oxygen barrier qualities of PET, but put a nice large screw-on lid on top of it. So when it comes time to clean up, you just unscrew the lid and you can easily reach inside to make cleaning a breeze.


At $65 (plus the cost of a handful of 2L pop bottles to empty out and turn into ice packs), the Cool Brewing Bag and FastFerment Cooling Jacket offer a great entry price point for experimenting with lagers. The temperature control is surprisingly good, so you won’t be wasting your money. I can’t guarantee you’ll love changing the ice out daily, but these can get you good results, and keep you within your budget.

The Cool Zone Brewing system steps it up to precision level control. It’s a big price jump, but depending on the amount of equipment you may already have, you can limit your expense. The simplest kit starts at $150, and the full kit is $319. You do need to tend to it during the fermentation process to ensure you keep the cooling water cold, but your efforts are well rewarded with great temperature control.

The BrewJacket immersion chiller initially comes off a bit snoozy. It looks almost too simple to really work, and the rate of temperature change if you’re trying to drop the temperature several degrees seems to confirm your initial suspicions. But once you get to your setpoint temperature, the BrewJacket really shines. It holds your temperature effortlessly, and all you have to do is keep it plugged in. The convenience doesn’t come cheap, but if you’re willing to pay the $300, you can keep your ice in that lesser-used side of your beer fridge.

Note: The next part is my findings from doing a trial batch for each type of system. Feel free to jump to the comments, or check out the extra information below.

Lager Fermentation Trial

I set up a controlled study to evaluate three of these different systems while fermenting a lager. To make things consistent, my local brewery (Farmington Brewing in Farmington, MI) was kind enough to provide 15 gallons of hopped wort from their Summer Citrus Ale (typically they ferment this to make a Saison at the brewery), which I split equally between three fermenters. I then made a giant starter, using two packets of White Labs Mexican Lager Yeast. This starter was pitched incrementally into all of the fermenters at the same time with the beer at ~55°F, and my basement at 64°F.

My fermentation schedule was two weeks at 50°F, followed by two weeks at 55°F with a second dosing of orange peel added (as the brewery does while in secondary), and then a brief cold crash before bottling. To test the systems’ capabilities, I attempted using each system to cold crash. Each batch was bottled with priming sugar, labeled, and then put into cold storage for cold lagering at 34°F. After six weeks of cold lagering, the initial bitterness of the orange peel had subsided, and it made a nice citrusy lager. Since the recipe wasn’t specifically tuned yet to this yeast/lager profile, a taste test wouldn’t necessarily create a differentiator between the systems. None of the three had any fermentation error tastes detectable.

Below are some plots of the temperature data, with notes of some interesting observations within the temperature control periods.

Entire Cycle (2 weeks @ 50°F, 1 week @ 55°F, 2 days cold crash)

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2 Week 50°F Control Point

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A: BrewJacket initially showed a higher temperature as thermocouple on outside of carboy mainly was picking up temperature of insulating bag until things started to cool off significantly.
B: Through majority of the experiment, ice bottles were changed out every 24 hours in both Cool Zone system and Cool Brewing bag. At one point, I stopped changing out ice on Cool Zone as it didn’t seem to need to be changed every 24 hours. However, I found out what happened if you don’t change it frequently enough as the temperature climbed 8 degrees in a 12 hour period as the ice fully melted at some point.

Typical 1-week Control Period (at 50°F)

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Note: Data from BrewJacket is based on display on control head, which does not show decimal place, so rounding occurs to next highest or next lowest full 1°F.

One Week 55°F Control Period

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A: I went away overnight in middle of this period for 48 hours, so I loaded up the coolers with ice. The Cool Zone System was able to maintain control temperature, Cool Brewing Bag lost the ability to control as ice melted, and the temperature went 7°F above desired control temperature.

Two Day Cold Crash

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Set control temperature on Cool Zone and BrewJacket to 34°F, and added as many 2L bottles of ice would fit in Cool Brewing bag around the fermenter.

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