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I'm conscious this is the third question I've asked before I even get started on my first brew, but hey-ho; better to learn from the experience of others and get as close to "right" first time.

I am about to start an ale brew and understand the ideal temperature for fermentation to be effective is in the range of 18 degrees centigrade (c. 64F) to 22 degrees centigrade (c. 72F) - maybe even 20-22C.

My problem is that where I live currently (north west England) the outside air temperature is a crisp 4-8C during the day dropping to freezing at night. The impact of this is that even with regular central heating, the best indoor range of air temperature I can get is between 15C (lowest) and 18.5C (highest) - having taken regular test readings at intermittent intervals throughout a few days - and I am not sure how these factors would impact on the temperature of my brew and fermentation. I don't have a home thermostat in order to keep a constant, so the indoor temperature fluctuates with the timed on/off intervals of my central heating (presently 1.5 hours at 6am, 1 hour at midday and 2 hours from 5-7pm).

I had considered a number of options to maintain a decent temperature including heat mats and brew belts and I am comfortable with the pros and cons of each and their potential effects on the brew. I have ruled out more expensive thermostatic options as too expensive to blow on my first brew.

Does anyone have any thoughts on how they would maintain a suitable temp during fermentation with these conditions? Has or does anyone currently brew ales in these conditions with positive results?

Interestingly, I have read that active fermentation can warm a brew by 5-8C, so assuming I get the fermentation going in the correct range, is it possible that the heat given off during fermentation could actually keep my brew in the correct range anyway?

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  • What kind of heat do you have in your home?
    – brewchez
    Jan 25, 2017 at 17:49
  • Gas central heating
    – user14585
    Jan 25, 2017 at 17:57

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I live in the south of England where it has recently been even colder than "oop North". At this time of year I go with the seasons and brew the year's supply of lager(!!!). Its perfectly lagered and crisp by summer.

However to answer the particular question - yes, I brew ales, light and dark, during the winter months at "less than room temperature" and they turn out perfectly. Of course beer is a matter of taste and some prefer the fresh (slightly) "fruity" flavour of beer fermented at higher temperatures others prefer a crisp IPA fermented at lower temperatures. But whatever, beer will ferment just fine at 10C or 15C, it just takes a little longer. Think (for example) 14 days instead of 10 days for primary fermentation. As in most brewing, the time is slightly irrelevant. The main factor to judge progress by is the specific gravity (density) of the brew. Maybe it is yeast type dependant - I have heard that "Turbo yeasts" that make up to 21 percent ABV require a rather narrow range of temperatures to achieve their stated attenuation.

If one decides one must ferment at higher temperatures, then I find a heat belt can be better than a heat pad - but both will work. If it is very cold then additionally part wrapping a blanket (or similar) around the fermentation bin will usually do the trick. I have even placed the brew bin next to a radiator, there was definite temperature cycle in the wort from day to night but it did not seem to affect the beer.

Large fast fermentation can heat up and even require cooling in very hot weather. But in UK it is rare to get a "normal" brew to heat appreciably while fermenting. I have possibly noticed a few degrees rise in an insulated brew bin but nothing I thought I should counteract. The "Turbo yeast" instructions state that the fermentation should work well for 25 litre batches but advises against doubling the batch to 50 litres as the "heat produced could adversely affect the fermentation". But that is the only stated case that I know of.

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    Thanks, interesting and good to know. I also read a clever thought on a blog just now where someone suggested a submersible aquarium heater in a tank of water as a cheap(er) means of regulating and means monitoring a thermometer strip is also easy. That being said, comparing the price of one of these to a belt doesn't seem too far apart.
    – user14585
    Jan 25, 2017 at 13:09
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Remember that yeast are living things and will regulate their own temperature as best they can. I've kept fermenters in rooms with an ambient temp around 18C and the yeast raised the fermenter temp to about 20C. You could also help them by wrapping the fermenter in an insulated blanket.

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    Yeast do not have the ability to regulate their temperature. Fermentation does produce some heat, but that is not to be confused with the idea that if put in a cool environment the yeast somehow generate heat to attain the ideal fermentation range.
    – brewchez
    Jan 25, 2017 at 17:49
  • Maybe "regulate" is too strong of a word. We can agree that they produce some heat during the fermentation process. Having said that I've had fermentations hold very consistently to 20C (68F) in a room with fluctuating ambient temps. I don't know how to account for that.
    – Tom L
    Jan 25, 2017 at 20:17
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    Its accounted for because water is a very good insulator. The yeast are slowly increasing the temp of the wort as they ferment, and the room is slowly sucking out the heat from the wort via the air around the fermentor. What you observed was the somewhat rare case where the heat generated by the yeast roughly equaled the heat lost to the room, for a certain amount of days. Ultimately the yeasties always stop working, and then the wort cools to room temp.
    – Graham
    Jan 27, 2017 at 19:45
  • Makes perfect sense!
    – Tom L
    Jan 31, 2017 at 3:33
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You can put your fermentor closer to the heat source in a room. If you have hot air heat you can put the fermenter over a floor vent and cover it with a towel or box. You can also only cover half the vent with a box/towel, placing the fermentor next too (not on) the vent. If you have radiator type heat the same techniques can work but you'll want to have the fermentor further away as radiators tend to get really hot. It takes a little trial and error but its a manageable means of having the fermentor be warmer than the ambient room around it.

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  • Really good suggestion, thanks. Only drawback with that is having to keep the radiator on constant to "maintain" the temp which means the central heating for the entire house being on. Doing that would sky rocket the gas bill. One day when I win the lottery, though, it will be brewtastic winters!
    – user14585
    Jan 25, 2017 at 19:25
  • Actually that's not really the case. It doesn't stay on all the time to maintain a certain house temperature. All you are trying to do is to capture a higher ambient temperature for your fermentor. Putting it closer to the heat source does that. Keeping the fermentor insulated in between heating cycles should keep it from varying too much.
    – brewchez
    Jan 26, 2017 at 1:24
  • Certainly worth a shot if I feel the fermentation is going a bit sluggish to begin with. Will keep it in mind. Thanks.
    – user14585
    Jan 26, 2017 at 10:27
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water bath and aquarium heater, or buy jacket.

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