I'm assuming that this should be done before racking when "primary fermentation" is complete? I suppose I have another question then too. Is there any way to estimate what the FG should be based on initial gravity and style? Or does it completely depend on hydrometer readings and time? When I do a diacetyl rest how warm should I go? Temp range is 64-74F.

I pitched a little high (78F) but got the temp down to about 65F before there was any activity at all. My initial gravity reading was around 1.07. The recipe is for a "Wet Mountain IPA" clone.

This is my first batch and the advice here has been very valuable, thank you.

2 Answers 2


Do you actually have diacetyl? Ringwood is a known diacetyl producer, so you should expect to, but nothing beats actually detecting it. :) For an ale, you should be able to just leave the beer at fermentation temps, and the yeast will keep working to clean up any diacetyl they've produced. If it were a lager, you'd want to raise up to ~68°F with a few gravity points remaining to let the yeast do their thing.

You can estimate FG based on the listed apparent attenuation of the yeast, plus an understanding of the fermentability of the sugars in your wort; if you added a bunch of crystal malt, you'd expect the FG to be a bit higher, if you added table sugar/honey, a bit lower. Yeast health and fermentation temperature will factor into attenuation, as well. As for what your FG will actually be, yes, go by gravity readings and time.

  • +1 for trying beer to see if it has diacetyl in the first place!
    – Poshpaws
    Nov 30, 2011 at 16:34
  • Thanks that's sound advice. I've been tasting at each stage and I was planning to for the next two gravity readings. I'm just a little anxious with this being my first batch and wanted to know ahead of time. Thank you for the help. Nov 30, 2011 at 16:40

My interpretation of a "diacetyl rest" is to simply to leave your beer in the fermentor for a number of days (~2-3?) at 65F after you have achieved constant FG readings. This will allow remaining suspended yeast to remove residual diacetyl which is probably not what you want for your beer style.

Since this won't harm your beer in any way, you mind as well do it for peace of mind.

In addition to what jsled has said regarding FG, you can also use free (or paid for if you wish) brewing software applications which can do the calculations for you. Examples include beer calculus and qbrew.

See here for an extensive list.

  • No problem. There is a lot of good stuff out there.
    – Poshpaws
    Nov 30, 2011 at 18:24

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