Cold Weather Fermentation Tips


It’s winter time again. (Photo by Joe Colby.)

Winter is here (in the Northern Hemisphere), and homebrewers living in colder climes may encounter situations in which cold weather affects their fermentations. When most homebrewers think of controlling fermentation temperature, they think of modified chest freezers or fridges to cool their brews. (Lacking that, the wet t-shirt method may be employed.) However, in cold-weather locations, fermentations may cool down to the point where they become sluggish or even stop. Here are some tips for keeping your fermentation temperatures up (and somewhat level) during cold weather.

Conserve the Heat You Have

For starters, be sure to conserve the heat that you have. When chilling your wort, watch the temperature closely and stop when you reach the top end of the yeast strain’s recommended fermentation temperature range, or maybe even a degree or two higher. With cold winter tap water, it can be easy to chill your wort past your target fermentation temperature, only to have to warm it in the carboy.

Insulation is key to keeping homebrew-sized fermenters warm in an overly cool environment. And be sure to not only insulate the fermenter from the surrounding air, but from the surface if rests on. Setting a carboy or fermentation bucket on a cold, hard floor can rob it of heat. Put a folded blanket or sheet of foam insulation under it. Insulating homebrew fermenters with shirts or blankets not only slows the loss of heat from the fermenter, it traps heat from the fermentation. Inside heated homes or apartments, this may be all you need to maintain proper fermentation temperatures.

And of course, in any house or apartment, different locations vary with respect to temperatures. It’s almost always cooler near outside walls or windows than near interior walls. In addition, when the furnace kicks on, the hot air enters the room somewhere. In some cases, simply moving your fermenter to a better location may solve your problems.


Heating Homebrew Fermenters


Don’t overdo it when applying heat to a homebrew fermenter.

There are special heating “blankets” (FermWrap), heating belts (Brew Belt) and heating pads (Brewer’s Edge Heating Pad) that are sold for homebrew fermenters. Some homebrew shops have store brand versions of these. If your fermentation space is likely to be 15–20 °F (8–10 °C) below your fermentation temperature, these can help. These can even be used in conjunction with a temperature controller — as with a converted chest freezer — to better control fermentation temperatures. Likewise, in the coldest conditions, these can be used within an insulated space — such as an old appliance box, an unused fridge or home built fermentation chamber — to further conserve heat.

A brewer may also have electric blankets, heating pads or other heat sources designed for other purposes (for lizards to bask on or to spout seeds early). If you are going to try to rig up something on your own, McGyver-style, be sure the heat output of your device isn’t too high. The products designed especially for homebrew fermenters are low wattage (15–40 W), so they won’t overheat your fermentation. Always test any “homebrewed” solution for temperature control on a fermenter full of water before using it on an actual beer fermentation.

An inexpensive alternative to heating multiple fermenters is a space heater. These days, space heaters are cheaper, more energy efficient and safer than they were 20 or 30 years ago. And most offer variable levels of heat output or even some level of programability (for example, to turn on and off at set temperatures). If you’re using a space heater, measure the temperatures around the fermenter(s) after the heater has been running for 30 minutes or so. Ideally, you’ll want the air temperature to be roughly 5 °F (2.5 °C) below your intended fermentation temperature. (This depends on a few things, so experiment a little). And, you don’t want one side of the fermenters to be hot and the other side cold. Moving the space heater away from the fermenters and having a backdrop (such as a wall) behind them to trap heat can even that out. The environment around your fermenter(s) shouldn’t be hot, or even warm, so don’t just park the space heater next to it and crank it up. Use a lower heat setting and keep the heater at a distance. And of course, most importantly, check on the temperature of the actual fermenting beer. Those stick on thermometer strips will give you reasonable estimate of this.


Unheated Garages or Sheds

If you are stuck fermenting in an unheated garage or shed, do not ferment in glass carboys. Even if you have a plan to keep your fermenters warm, ferment in plastic in case something goes wrong and the beer freezes. Modified freezers or fridges don’t provide heat (obviously), but they are insulted. Combined with a weak heat source — such as the heat “blanket” or belt — they can work well. Unplug the freezer or adjust your thermostat so that your heat source and refrigeration don’t end up battling it out. And of course, keep a close tab on fermenter temperatures.


Changes in Temperature


The weather outside is frightful, but the beer can still be delightful . . . if you keep the yeast in a temperature range they can tolerate.

In winter, most people turn their thermostat down overnight (or program it to do so automatically). If the temperature in your fermentation space oscillates every day, the temperature of your fermenting beer will too. And, it’s much easier on the yeast if the fermentation temperature is held reasonably constant. The temperature in the fermenting liquid won’t vary as much as the surrounding air temperature, but it will slowly change. In the absence of active temperature control, adding a little bit of extra insulation at night could help smooth out the temperature swings.

In addition, early on your fermentation will be generating heat proportionally to the vigor of the fermentation. And, increased heat spurs a fermentation to be more vigorous. This can cause a positive feedback loop. Be careful around high kräusen that your efforts to warm the fermentation don’t lead to a spike in temperature. After high kräusen, when the fermentation starts slowing, you’ll likely need to add more insulation or actual heat to your fermenters. At the very end of a cool fermentation, it may pay to heat the fermenter to the top end of the fermentation range and rouse the yeast.


Kick Saving a Crashed Fermentation

If your fermenter does cool down to the point that fermentation is sluggish or stopped, you have a fair shot at restarting the fermentation if you heat the fermenter gently and rouse the yeast. The key is heating the formerly fermenting wort gently. One solution is to fill your bath tub most of the way with water that is roughly 10 °F (5 °C) over your target fermentation temperature. Do not pour a hot bath for this. Set the fermenter in the tepid water and let the fermenter gradually warm. Replace the water as needed, but again, don’t use hot water. This may take a few hours, depending on how cold your fermenter is, but slowly raising the temperature is the key. (Also, you don’t have to sit and tend the fermenter, just check the temperature of the bath every 20 minutes or so.)  Once the liquid inside the fermenter is within the high end of the fermentation range of the yeast, swirl it to rouse the yeast into suspension. Keep the fermenter at the high end of the fermentation range while the yeast recover.


The Silver Lining

The nice part of having a cool fermentation space is you can let the beer condition in the fermenter (or in a secondary fermenter) for awhile when fermentation is done. A couple weeks of cold conditioning (or even cool conditioning) in bulk can give the beer (even an ale) time to drop some of it’s chill haze (if present) and mellow a bit.

As with anything you do in your homebrewery, write down the actions you took to control fermentation temperatures (and how cold it was in your fermentation space) so you can plan ahead for next year.


If you enjoy Beer & Wine Journal, please consider supporting us by purchasing my book — “Home Brew Recipe Bible,” by Chris Colby (2016, Page Street Publishing). It is available from Amazon and Barnes & Noble. You can also find the nearest independent bookstore that sells it on Indiebound






  1. One very effective method I’ve uses for several years is to put the fermenter in a water bath with an aquarium heater. Since most aquarium heaters have built in thermostats, no need to get any additional temperature controller. And as we know from trying to cool down wort for pitching yeast. Water will hold heat better than air. I have found it does help to put in a small immersible fountain pump to circulate the water. For additional insulation, the fermenter can go into the same cooler used as a mash tun. (If the carboy fits with room for the heater.)

  2. Man, I wish too cold was a problem I had- much easier to fix than too warm. In any event, don’t underestimate the heating powers of a 40W light bulb if its a reasonably small area, life a cabinet or closet. I can keep my brew cabinet a good 10 degrees warmer with an old lamp and a 40W incandescent bulb. That particular lamp looks much better where it can’t be seen anyways.
    – Dennis, Life Fermented Blog

    • Chris Colby says

      Yep, light bulbs (the old type anyway) give off a fair amount of heat. Just remember to shield the beer from light if you use a light bulb as a heat source.

  3. “Modified freezers or fridges don’t provide heat (obviously), but they are insulted. ”
    Do these appliances really get insulted when they are used to keep mashes warm?

  4. Hi i am kavin, its my first time to commenting anywhere, when i read this piece of writing i thought i could
    also make comment due to this good piece of writing.

  5. Having a bit of trouble with a brew at the moment- basically, I had a heat belt going when I pitched the yeast, but the belt broke on day 2 and then I was lazy in fixing it. By the time I managed to re-fit it we were a week in and the brew was at 14C, obviously way too cold. Heated it back up, put more yeast, stirred brew around to simulate old yeast but still no fermentation. I’m guessing I heated it up too quickly? It’s a shame because it’s now been 4 weeks and no fermentation, probably going to have to throw it out since I’m going away for 5 weeks tomorrow. Oh well, learning experience I suppose.

    • David Corless says

      Did you actually check the gravity? I wouldn’t be surprised if the brew did finish fermenting…

    • never throw beer away! Taste it and see (or check gravity) – if there is sugar in there, the yeast will find a way to get at it. by the by, five weeks in the high 50’s sounds like some quality conditioning time to me. But how’d you find a spot that cool in august?

  6. My wife put my mash outside in freezing cold weather. Is it still good. Only part of it was frozen

  7. jason thornton says

    dose it matter if i have my brew down for 3-4 days then put it on my heat pad as i have 2 brews on and only one heat pad

  8. Ale Marcuzzi says

    I know this product called Hot Box and I think this could be a great choice to keep the temperature of the fermenter controlled, thanks to the thermostat. Maybe you can think about it.

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