Beer was getting cold so in a desperate attempt to raise the temperature I put near boiling water into the container. So 450ml into 23litres of beer. The beer had only been brewing for 4 days.

Will the beer be OK, or have I killed the yeast?

Edit: I can confirm that the yeast survived. The gravity was originally 44 when I started and after the "boiling water" incident it was 22. It eventually ended up at 9. So I'm pretty sure it survived. Won't ever risk it again though.

  • 1
    What were the temperatures before and after? Commented Sep 17, 2013 at 18:35
  • Also would be good to know gravities - starting gravity, before you added boiling water, then say 24 hrs after boiling water...
    – paul
    Commented Sep 17, 2013 at 18:46
  • Temperature before hand was 15 and going down. Temperature afterwards in total was ~22. Im guessing the direct contact of boiling water would kill spme of the yeast off, but the rest should be ok.
    – Navigatron
    Commented Sep 17, 2013 at 20:00
  • Haven't checked gravity before and after
    – Navigatron
    Commented Sep 17, 2013 at 20:01
  • 1
    1.044 to 1.009 is 80% apparent attenuation, which near the maximum you can expect from any yeast. Congratulations. You've made beer! Commented Sep 26, 2013 at 5:03

3 Answers 3


If you add near boiling water to fermenting wort, then yes, you can definitely kill some of the yeast, at least, any yeast that come in contact with that near boiling water. If there was enough yeast in the fermenter, distributed in other parts of the beer, then a lot of it may still be alive. If you see signs of fermentation (bubbling airlock, krausen) it worked. If you don't, it still may be working but you'll need to check the gravity a few times to know if it's woken back up.

In the future, you should not do this again :) You can warm it up by other means, and generally, unless it has gotten very cold, you can wake the yeast up again. You can

  • move it to a warmer spot (next to a heater/radiator)
  • use a brew belt or electric heating pad to warm it up slowly. You can add insulation, blankets, coats, etc to keep heat in.
  • put it in a sunny spot, completely covered in something dark to block out the light and absorb sunlight/heat. Blocking the sun is important to avoid skunking the beer, but you can still use the sun to heat it
  • put the fermenter in a warm water bath

With all these methods, the temp needs to be monitored so you don't overheat the yeast. Once it's warmed up, you can also add some more DME, sugar or honey in a solution of boiled water, cooled down first to help activate the yeast, or add more yeast.

  • Cold house, no heating. Next time its going in the bath. Thank you! Hopefully, it didn't kill it off. I will have to monitor the gravity.
    – Navigatron
    Commented Sep 17, 2013 at 19:59
  • 2
    450mL in 23L is really not that much, I'd guess it will be fine. If you google for 'swamp cooler' you'll see a lot of people use coolers with ice water for fermenting in the summer w/o refrigeration. You could do the same thing with the warm water bath.
    – paul
    Commented Sep 17, 2013 at 21:35

I don't think the near boiling water on its own will cause any harm. But unless you boiled it for a few minutes to remove oxygen before you added it, oxidation could be a problem.


The yeast will be fine; I don't think you could have raised the temperature by more than 4 or 5 degrees F. That's not enough to harm the yeast, but it may result in increased ester production, giving the finished beer a fruity aroma. The beer will also be diluted a small amount, which is not a good thing.

When raising the temperature of the fermenting beer, you want to do it slowly to avoid shocking the yeast. Adding boiling water is not the best way to do this. Instead, try moving the fermenter to a warmer area, or use a brew belt to gently bring up the temperature. Sometimes, just adding an insulating layer (and old blanket, for example) is enough. The fermentation process produces heat, so if you can prevent that heat from escaping the temperature will rise.

  • I'm looking into getting a brew belt. Thanks for the tip :)
    – Navigatron
    Commented Sep 27, 2013 at 14:46

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