I am having some issues keeping the temperature controlled. I live in SE QLD and the daily ambient temperature has been 23 degrees C down to 11C. I've been advised not to let the wort drop below 18C but it has been lower, about 15C with a high of about 22C. I would like to know
1 What are the ill affects of this (other than the yeast becoming inactive)
2 If I leave it a bit longer and get the temperature regulated (towels and a heat pad) Would I be ok to leave it for a couple of weeks and then check the hydrometer before bottling?

  • What yeast are you using?
    – Sneftel
    Commented Jul 8, 2014 at 16:37
  • I have just used the yeast packs included in the cans of Morgans brew kits.
    – Snarf
    Commented Jul 9, 2014 at 9:39
  • Reading the stockist website I am fairly sure that I am using Saccharomyces Cerevisiae morgansbrewing.com.au/products/hops-yeast. It seems to be the standard one that they supply.
    – Snarf
    Commented Jul 9, 2014 at 20:56
  • @Snarf, WOW, I do not trust that site's yeast description at all. They say its a "Lager Yeast", but identify it as Sach. Cerevisiae (lager yeasts is actually Sach. Pastorianus), and they say to ferment it ideally at 22C/71F and up to 32C/89F, which is FAR outside the temp range for all lager yeast anyway. For your next batch, order some dry yeast from Fermentis instead.
    – GHP
    Commented Aug 12, 2014 at 13:38

3 Answers 3


Idiot-proofing the fermentation temperatures has been a bit of a peeve of mine right now, as I use a family member's basement as a brewery and I have little control of the ambient room temperature.

The DIY solution I am working on uses a $15 digital thermostat/controller with a sinkable probe from Ebay to switch on/off a typical brewing heat belt (a FermWrap would be better if I had one) at set temperature thresholds.

Follow this video tutorial on YouTube, plug in and install the heat belt and sterilize/sink the probe into the beer.

I have seen people use this system to activate a space heater for entire brew rooms, which might be economical if I wasn't using an entire basement.


Yes, you will need to extend the fermentation time, as cold will slow down the yeast's ability to reproduce and ferment. Your best bet is to get a temperature controller (e.g. STC-1000 or Johnson digital controller) and accompany that with your heat pad or a purpose built FermWrap from MoreBeer.

Worst case, you don't attenuate all the way, and then when you bottle, you risk the yeast kicking back into action and over-carbonating your bottles with dangerous consequences. Less pessimistic would be to have them drop off too early and you'd have a sweeter than normal beer. Other side effects include flavor production depending on the yeast used. Some yeast produce certain flavor compounds at certain temperatures. Take a typical Hefeweizen yeast such as WLP300. They tend to produce more clove flavor at below-optimal temperatures, and banana at above-optimal temperatures. To balance them, you would need to ensure proper fermentation temperature.

Also, if you can steady the temperature with heating & cooling, your temperatures sound like they'd do well for lagers.


It's not as bad as you think. Remember, you have 20 l of beer. It takes time to warm it up and time to cool, so temperature fluctuations in the fermenter will be smoothed. I would wrap the fermenter in a blanket and leave like that for the normal fermentation time.

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