How Critical Is Temperature Stability?

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While i realise that it is important to ferment between 18- 22C, how critical is temperature stability? I can maintain this temperature range ok, but of course my brew fluctuates between these temperatures during the day from 19 to 23C. Is there any benefit to holding the temperature constant at say 20C... will i notice a difference?

I'm not sure what the bad effects are, but you don't want too much variation. I think the yeast doesn't like the shock of changes. You gotta look after the little buggers. A degree or two each way should be nothing to worry about.

Having said that, I've had some huge variations (like leaving a heater on over night) and the brew still came out ok.
Its a thing that you would like to be constant.
Coz my house get so hot and I have nowhere cool to ferment in the summer I am at the mercy of the weather. I have had huge variations ranging from 16 to 30 for the one brew. I dont like it but theres nothing i can do about it. when I see it getting up to 26-28 i try the wet towel trick but that doesnt seem to help much.
So far though I havent had a brew go off and they have all been very drinkable.


When they have beer in them, my fermenters are always wrapped in at least one towel. In hot weather it's a wet towel. In cold, sometimes a blanket.

The idea is, firstly to keep the light out, but mainly to insulate and keep the temperature fluctuations down.

I do this even in secondary when primary fermentation is finished and they are sitting around clearing and waiting to bottle.

a wet towel on its own does SFA to lower temps. You need to have a fan aimed straight at it on high. I also put a large block of ice (bowl left in freezer overnight) on top every morning. It keeps the general temperature down and keeps the towel wet as it melts. You can lower the temp by about 5 to 7 degrees like this.
Ok deebee,
i can see where you are coming from.
But if i'm gonna go thru the hassle of freezing ice and aiming a fan at it I might as well get a second fridge with a thermostat and do it that way.

yep :) use prob the same power, and get a adjustable thermostat and you are laughing, lager, ferment, 2ndry/ dyacetlerests and cc

you got it all :)

Its a expence but now that i have it, i rate it very high on the list of things a brewer needs esp for light beers and very esp. for lagers
I'm lucy in that my garage is a virtual bomb shelter. It's a concrete box under ground cut into rock. It let's no light in and stays a constant 22 - 23 in summer, perfect for ales. I have yet to crack a larger but I'm hopeing the cooler months will bring the temp down to the required levels. Probably not the first thing you'ld be looking for when buying your next home. But a well insulated garage takes a lot of temp worries out of brewing.
It can cost very little to set up a fermenting fridge and brew at a constant temp. I went to a bloke who repairs fridges and sells second hand ones and asked him if he had any old ones that looked ugly but still worked, he sold me one for $10, a 0 to 40 thermastat you can buy for $35, allow $10 for incidentals and your've got it. My ugly old fridge has been going now for 5 yrs with no problems.
cheers Fingers.
Johnno yep no doubt a frig would be easier. I don't have the room for it.

A fan is much cheaper to run than a frig but the frig is definitely the go if you have the room. I agree the towel and the fan is a hassle but if you brew in summer without a frig, I don't yet know a better way.

(...and going back to where this thread started, a blanket or a couple of towels around your fermenter will decrease the fluctuations in temperature.)
i dont think a fridge will use much power at 20deg. Its insulated so well the only work it is doing is combatting the exothermic reaction of the yeast (not that many joules of energy)

dont forget the compressor would come one maybe once in the day or even 4 times a day. wouldn't use much power to keep it at 20deg.

the fan will need to run constantly to keep it cool so i think the price difference would be very small.

When you lager it will use more but its unfare to compare a fan to a fridge since they would achive the same result (fan will never get the brew to 9deg or 0deg for lagering)

DeeBee - theres gotta be room for such a life saving device :) store your hops and yeasts etc in it also!!! (thats what you tell the misses "it will get all my brewing gear out of your fridge" hehe)

Also a insulated box work's well for brewing (old dead free fridge iif you have room) are cheap and work well. Add frozen ice bottle to cool ???
Some friends of mine built one of these : Son of Fermentation Chiller.

They got right into it, built a circuit to control the fan etc etc etc. The downside is the cost of decent insulating foam. Upside is that they can brew lagers @ 7C with an ambient temperature of 24C. They use a couple of frozen 1.25 litre PET bottles. As the weather gets hotter, you just swap them into and out of the freezer more often.
OK I printed out this link by PoMo a couple of months ago and left it in the bog. Have read it quite a few times now. Now have priced the bits and pieces, probably come out at about $120-150. Thinking very seriously of making one. Even though I have talked my wife into getting a brewing frig, space is my problem and I just can't figure out where I can put a frig in my house, even a little one, so this option is looking good for temperature control.

Advantages over frig: smaller, easier to store when not in use, cheaper to run, it will be fun to make.

Disadvantages: costs almost as much as small 2nd hand frig, more effort to use than frig, limited capacity for lagering and other frig-type uses, I will have to make it.

So I'm still in the balance. I was just wondering if anyone had made one or had any tips before I go ahead and learn from my mistakes.

PM, your friends who built one, are they happy with it? Does it give good stable temps? Any major hassles?

All responses appreciated.
Gday All

Just having a bit of a think about this fermentation box idea that the "Son Of Fermentation" is built from and that it states it uses the polystyrene foam. and we all know how weak foam is...

As my sister had just built a house using polystyrene foam (dont know the real name of the stuff theyactually use) and the stuff is quite tuff they reckon it is very unbreakble what makes this foam strong is the outside layer they attach to the foam

I think if anyone is serious in making a cold fermenter i would go and look at new housing estates and have a look at the houses that are using this materil to build there house with and have a yarn to the builders to see if you can get a few of the offcuts so that you could use also what help may offer him a couple of ya homebrew ;) :) so that you can score decent piece of cut they may even cut the piece to length ...or wait till they all go home and then have a scout around :ph34r:

The thing is this stuff will make your fermentation chiller look very proffessionel and can be painted to suit the interior of your brewing room or just leave it as is if ya just use a the luandry

also if ya got an old pc lying around the house that is not in use maybe a perfect solution to use for the fan

just an idea to think about and if you intend on using this stuff make sure you have plenty of saw blades as the blades will go blunt pretty quick

cheer and beers
I have made a son of fermentation chiller.
It works out quite cheap if you have most of the materials.
For the foam, go to a foam supplier + bring your measurements with you.
Ask for insulation foam (grey in colour) and then ask for it to be cut to size.
They use a hot wire to cut it perfectly. (with an additional cost or a few brews!)
All the cuts will be perfect and all you then need is some liquid nails to join, I used a computer fan + digital thermometer. Didn't worry about a thermostat.
Can keep the temperature up here in the tropics from 34C to 20C which is good for ales. The humidity plays effect on the bottles though, they need to be replaced twice daily. A dry climate probably will be better in achieving lower temps.
Give it a go, it's fun. it is quite big though and awkward to move around.
OK Guys im getting pretty keen to make one of these things. I was wondering if using dry ice would be better than PET bottles?
Gday Sjw

it costs around 20 bucks for 6kg block (air liquide) but will last upto 4 days approximately

if you were going to be making one of these contrataptions i think dry ice could be a good possibilty but also could be very dangerous with some of the gases it provides so i would be very careful in using dry ice and always use gloves using it


Dry ice would work really good - no liquid when it melts!
I would only be concerned that it may get too cold? probably not though.
Only reason I wouldn't do it is because of the cost.

Ozdevil - what dangerous gases does it produce? I thought it just sublimates to give C02?

With the PET bottles you just put them in the freezer to re-charge. Keep rotating your bottles. And there is no water from melting, just a little condensation.

The foam is 50mm extruded polystyrene. Quite rigid and extruded in one piece rather than made up of little beads. A sheet to make the box in that link costs $65.

Siiren, how do you adjust temperatures without the thermostat?
G'Day all,
If you fellas are looking for polystyrene foam sheets I have found a good source.
Any auto tyre service shop that deals in car and truck batteries in a big way will have sheets about pallet size or 1.2m x 1.2m approx.
When they ship auto batteries from the manufacturer they sit the batteries on a sheet of foam which is between the batteries and the pallet.
I got as much as I wanted from the local Goodyear Tyre Service and they were happy to get rid of it.
You would need to let them know you want some as it usually gets broken up and tossed in the bin

FWIW you could have a fridge outside in a shady spot and it would work just fine.
If security is a problem just put a lock on it - space problem solved.

IMO a fridge and temp control is much more reliable as it is set and forget.
Nothing worse than being at work on a hot day and worrying about the beloved brew that you spent 6 hours mashing and boiling a few days before.

deebee said:
Johnno yep no doubt a frig would be easier. I don't have the room for it.
Then you have no choice, move house.

The most popular page at the brewiki is the temperature control page. Last time I spoke to the dude at refrigeration parts victoria he only had a couple of Fuji Koki's left and had quite a chuckle about homebrewing.

I haven't been into brewing long (less than a year) and I have tried a couple of lagers with no dramas. Even for ales, keeping one eye on the weather while brewing is a pain.