What different methods do people use to maintain or control fermentation temps? This includes maintaining temps for both Ales and Lagers. For most climates, active control is necessary for doing lagers. However, I have seen multiple neat tricks people use for maintaining ale temps outside of ambient temps.

This also includes not just keeping your beer cooler when its warm out, but also warm enough when its cool out.

Post your methods and discussions here as this is a community wiki.

16 Answers 16


For the most consistent results, a spare fridge or chest freeze and a Johnson control is the best setup. No need for a Stopper Thermowell, just tape the temperature probe to the outside of carboy, and cover the probe with a scrap piece of styrofoam and tape -- that way, you ensure you are getting the temperature of the wort rather than the ambient fridge temperature.

To cool, just plug the fridge/freeze into the Johnson controller (set on cooling setting), with a 2 degree variance. Keep in mind that the recommended fermentation temperatures written on the side of the yeast bottle are mostly wrong -- consult with Brewing Classic Styles for a good indication of the fermentation temperature for a particular style.

If you were doing a classic German Pilsener, you might start your fermentation temperature at 50F for the first 10 days of fermentation, then bump it up to 60F to drive off diacetyl, then slowly reduce the temp over a period of several days down to a lagering temperature of 36F for 30 days. Then bottle (with priming sugar), or keg. I will often drop the temp on ales as well to 36F for several days before bottling, as it aids in clearing the beer.

To heat, you can use a number of different heating sources. I use a dehydrator bottom, but others use a low wattage space heater, a heating pad, a Brew Belt, an Electric Fermentation Heater wrap, or even a low-wattage light bulb. Be cautious when choosing a heating source to avoid fire and appliance warping. Both Northernbrewer.com and Morebeer.com have a variety of heating sources. Again, using the Johnson controller, just plug your heating source into the controller (set on the heating setting).

Also, because you are maintaining the optimum fermentation temperature, you are also likely to generate lots of blowoff during the first couple of days of fermentation. I recommend that you use a large blowoff tube placed into a milk jug of water.

See Düsseldorf Domination! for an example of a fridge/digital controller/blowoff setup.

Happy Brewing!

  • You've mentioned taping the thermostat probe to the outside. I use a bottle of water in the fridge with the thermostat inside. I've had no troubles yet but is there anything that could go wrong with this setup? Commented May 1, 2011 at 7:18
  • @C4H5As the reason to tape your probe to the carboy is that you want to measure the temperature of fermentation, not the temperature of the fridge. You might not notice a large difference most of the time, but when you're first normalizing the temperature of the beer and as the yeast is ramping up your bottle of water will be significantly behind the temperature of the beer.
    – sgwill
    Commented Dec 22, 2011 at 18:18

See also: this discussion. And the HomebrewTalk wiki page.

Controlling fermentation temperature is one of the best things you can do to make good beer!

One of the most basic ways to keep your brew cool is the swamp cooler method. Put the carboy in a tub of water and throw a towel over it. If you keep a close eye on the temperature you can keep it in a good range with ice.

The wet t-shirt and swamp cooler method is probably insufficient for temperatures in the mid 90's. The temperatures in East Texas get stupid-hot eight months out of the year. Last year I built myself a duck-in cooler powered by a small window air conditioner. I can get the temperatures down to the mid-sixties, and probably further if I take apart the AC's thermostat. See my blog for details.

A fellow brewer recently donated a chest freezer to me and I had a Johnson Controls external thermostat. This combination is ideal for fermenting because the freezer fits a few carboys and the thermostat keeps the temperature within 3° F of your target. I made my first (real) lager, a CAP, in the freezer.

There is also a Low Tech Lagering DVD. I have not seen it yet, but I trust that James over at Basic Brewing Radio knows what he's talking about.

  • You can also add a fan to you swamp cooler setup. The fan increases the rate of wicking up the towel or T-shirt. Believe it or not it will get you another few degrees of temperature drop.
    – brewchez
    Commented Jan 7, 2010 at 20:52

There is brewpi

  • 2 stage controller uses PID to achieve much more accurate temperature regulation than simple thermostat controlled on/off controllers.
  • both heating and cooling
  • web UI, and lcd UI
  • supports constant fridge temp, constant beer temp as well as following a temperature profile

I use a big tub, fill it with water and have about half a dozen frozen plastic water bottles in my freezer at all times. During summer every morning i would toss a bottle in there.

If it's really hot throw a few in and monitor the water temp and the carboy temp. When they thaw take the bottles out and put them back in the freezer and use them again the next day and throw some frozen ones back it. A T-shirt is a good idea to because it sucks the water up some and keeps light away from your beer.

This method was pretty effective and if you can't do anything suggested here just brew a saison!

  • This is one of the cheapest methods also, for <$10 you can find a large tub at a garden or farm supply store that will fit your carboy or bucket.
    – JPicasso
    Commented Oct 14, 2016 at 13:30

The most straighforward method of performing temperature control is with a fridge and a thermostat controller.

I have used a standing fridge in the past relying on a Johnson Controller to maintain 68F temps. I currently use a chest freezer with the same controller. I have found that the chest freezer holds temperature better and doesn't need to cycle on and off as much as the fridge did. That is especially true in the summer when my garage, where I brew, is in the 90s at times.

I like to use a towel and duct tape to hold the probe against the side of my glass carboys. The towel folded over a few times helps to insulate the probe from the chest freezer ambiant air, and the controller is more reacting to the temp flux in the carboy. I'd probably graduate to ta thermowell at somepoint, but it requires a small monetary investment. I'll go that route when the current probe and controller finally burn out. Don't fix what isn't broke.



If you're not looking to spend a lot of money while keeping your fermentation temperatures lower in the warm months, you can set your carboy on a floor A/C register and turn a trash can upside down over the carboy. You could put it in a water bath as well (for more thermal mass and more temperature stability), but then you'd need an even bigger trash can to turn over on top of it!

Unless you adjust your house thermostat lower, this system costs $0 to operate (presuming you'd have your a/c turned on anyway). This is because the chilling captured under the trash can will eventually leak into the living area.

I have also seen a guy rig a bit of flexible ducting from a ceiling a/c vent, but he was single (I'd never be able to get away with that in my house).


For those where the controller must control both heating and cooling to maintain a set fermentation temperature, checkout the Fermentation Controller at:



Started home brewing earlier this year and so far have only been concerned with heating rather than cooling as I didn't do any during this year's long hot summer.

I put the fermentation vessel into a metal bath and filled that with enough water to cover a 300W Aquarium Fish Tank Submersible Heater. This has a temperature dial at the end which can be read while immersed. The heater cost around 15 pounds and was ordered from Amazon. It worked really well, with the water in the bath acting as a heating jacket for the FV, with no need to immerse the heater in the brew, and hence no need to clean the heater before use.


Living in Wisconsin I have the problem of keeping things warmer than the ambient temperature most of the year; especially since I'm a cheap bastard and keep it effing cold in my house during the winter. It's in the 40 degree range in my basement during the winter which is perfect for (or possibly too cold for some) lagers.

I recently came across this method for keeping things warm without having to purchase an expensive temperature controller (remember I'm a cheap bastard). I haven't tried it yet, but it seems like a sound idea and I'm definitely going to be giving it a try.


I am fermenting 10 gallon batches in single vessels that don't fit inside a chest freezer and the heat created by the fermentation itself seems to have a greater effect when the whole batch is in a single vessel.

I have a small utility closet that is insulated and inside there is a small space heater and a mobile air conditioner that vents out the wall. They are both hooked up to a Ranco controller but I'm about to switch them to a BCS-460. The mobile AC unit came off Craigslist and I already had the heater.

If you have the space, this can really work well if you want to have multiple batches fermenting at once without the space constraints of a freezer but obviously they all have to require the same fermentation temperature and this won't drop the temperature down low enough for lagering.

  • Do you concern yourself with differences among fermentors? I use a single fermentation chamber for two 6.5 gallon fermentors, and I am sometimes concerned that slight differences in fermentation will favor the fermentor that I have the temperature probe taped to. Commented Sep 26, 2011 at 2:22

Brewing ales in Madrid can be a challenge. Winters are cold (down to -10C/14F) and summers are hot (touching 40C/104F in August). I have found that when the room temperature is at or below ~25C/77F I can keep the carboy cool (20 litres) (as others have mentioned) by wrapping it in towels and putting the whole setup in a large container of water. The evaporation works well since this is a very dry climate, and I can get down to ~20C or lower which is fine for my purposes. Above this I have to put on the AC in the smallest room in the house. I only have to do this on rare occasions since we can usually can keep the room temperature OK with blinds/ventilation at the appropriate times of the day.

In winter, we have the central heating on and I can always turn it down/off in the brew room.

I haven't started doing lagers yet - my next project!

  • Update: The temperatures outside have just hit 40C/104F and inside 30C/86F. The "wet t-shirt" method is only getting me down to 25C/77F so I'm having to use AC. I think I need to look at getting a proper cooler.
    – Poshpaws
    Commented Jun 27, 2011 at 20:46

There's a lot of good information here, but I would strongly suggest against taping the temperature probe to the carboy. I've tried that approach, and it doesn't work.

It takes a lot of energy to raise five+ gallons of wort a few degrees. If you're controlling your heat source based on the wort temperature, by the time it registers that the wort is the correct temperature the ambient air temperature will be way too high, and you'll end up overshooting your mark every time. You'll spend the whole fermentation cycle chasing the wort temperature. Much like keeping your charcoal bbq at 225 by opening and closing air vents - you always overshoot one way or the other.

Just control the ambient air temperature instead. Know that active fermentation creates 4 or 5 degrees of internal heat, and plan accordingly. Use a cheap carboy strip to measure its temperature, stay on top of things, and you'll hit your numbers dead on every time.

  • I won't downvote this, but I've had great results with the method you advocate against in this post since I started controlling ferm temps, and most of the experts and multiple-award-winning homebrewers (Jamil, Tasty, and others) are in favor of this method. I haven't measured it with a thermowell and/or graphed my temp during active fermentation, but would be interested to know others' opinions on this. All that being said, you may be right!
    – Pietro
    Commented Nov 30, 2012 at 20:33
  • I thought the point of taping the probe to the carboy was that it takes a lot of energy to change its temperature. That way you won't have the compressor cycling so often.
    – JoeFish
    Commented Dec 12, 2012 at 15:59

An idea I want to try and would like comments on is to insulate the fermentation vessel and put a coil of pipe though the vessel. Then using a thermostatically controlled valve run incoming mains water to cool the ferment. This water will be consistently cold as mains pipes run through the ground whose temperature changes little between summer and winter in the uk. This should enable me to brew english ale but I not sure about larger.

  • Interesting idea! I was thinking of trying something similar - but instead using a closed loop and with a peltier to chill the water as it cycles around.
    – Tim
    Commented Dec 22, 2016 at 1:29

start from a good temperature controller for brewery, like Pixsys Atr 621. the support will suggest you what to buy and what to do.

  • 1
    More information would be appreciated. Are you suggesting it for a home brewer or a more professional brewer?
    – Philippe
    Commented Nov 11, 2015 at 2:15

I personally use fridge with thermostat (it stands in my flat, so it's never too cold for yeast), but before I bought a spare one, I used a more makeshift solution.

You have to build a large styrofoam box, big enough for your fermentor and some, but not too much, spare space. You place your fermentor inside and change frozen or hot water bottles when temperature gets out of range. This is a lot of hassle, I agree, but it's cheap and easy to do.


I made a styrofoam cooler and it's doing its job OK.

Get five 100x50x5 cm panels of styrofoam. Cut 4 of them to 70 cm and glue together to make a box. Add bottom and lid from the remaining piece of styrofoam. It should end up with 45x45x60 cm inside, enough for a standard 33 litre plastic fermenter.

Cooling is done with 1-4 bottles of water, frozen in a freezer. They need to be changed every 12 hours during the first stage of the fermentation, once a day later on. Just remember to place the bottles on a plate or other recipient that will collect the condensation from them.

This takes some practice and isn't too accurate: you can't control the fermenting wort temperature too much, but it's generally easy to lower it by 5C or so. And it's cheap. The same cooler can be used without the ice bottles to produce 28-30C temperature inside, suitable for fermenting Saisons.

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