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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > When to do a diacteyl rest
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Old 05-09-2013, 06:55 AM   #1
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Default When to do a diacteyl rest

I made my first lager an Oktoberfest 2 weeks ago as of tomorrow.. I was wondering when I should do my diacetyl rest? I am using Wyeast 2352 Munich Lager 2 at 54 to 56 degrees internal temperature. Also, the temperature range is 52-62 so what temperature should I bring it up to if I'm going to do one?

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Old 05-09-2013, 09:00 AM   #2
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it's an "ask 10 people get 12 answers" question. i like to point to the data from an austrian university, shown on braukaiser's wiki:
http://braukaiser.com/wiki/index.php...menting_Lagers
they measured diacetyl level in fermenting beers, and plot it against time while also showing extract (showing drop in gravity) and temperature, for a few different temperature regimes. basically this experiment says that if you just leave it cold for a long time (fermented at 9c and dropped to 1c) diacetyl continues to drop slowly even in the cold. so if you lager it properly on the yeast the diacetyl will f off. of course holding your ferm temp until diacetyl is gone will achieve the same result but faster. the two batches in the experiment where there was a diacety rest, one from 9 to 13 degrees and one from 9 to 20 degrees, both had the effect of very rapid decrease in diacetly. from the point of the home brewer, i doubt it matters which of these you do, as long as you do it towards the end of fermentation, as in the above experiment, so your lager yeast doesn't have the chance to get weird. i am not a hugely experienced lager brewer but when i brew them i ferment 9-11c and after 2 weeks i shut off the cooling to let it rise to ambient temp, which (since i only do them in the winter and in an unheated area) is nowhere near 20c, forget it for a week, then rack to a keg for cold storage. but that's just me

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Old 05-09-2013, 10:12 AM   #3
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You shouldn't have let the temperature get above 55 F while it's fermenting vigorously . It could probably lead to producing esters in your Oktoberfest which is not desirable .

Ideally you want to start the diacetyl rest slightly before reaching finishing gravity so that there is still active yeast suspended in the beer. In practice this is difficult to determine, and you need to look for a slowing in vigorous fermentation to start the rest. Look for when the yeast head has collapsed back into the beer and relatively few gas bubbles are coming to the surface, but before the beer shows visible signs of clearing.

Carry out the primary at the recommended temperature, then bring the beer temperature up to 65 °F . Hold it there for two or three days then cool gradually to the desired lagering temperature.

To see if the diacetyl rest is complete , There's an easy “forcing” test that will only cost you a few ounces of beer. Pull a sample from your fermenter and split it into two covered containers. Refrigerate one and heat the other to 140°F for an hour, then taste them both. If they taste the same, you're ready to rack your beer out of the fermenter. If you can taste butter in the heated sample, your yeast is still at work, and you should give it another day or two.

Hector

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Old 05-09-2013, 04:56 PM   #4
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I was planning on fermenting for 3 weeks so.. Basically you think I should ferment for 3 weeks then bring it up to 65 degrees and hold there for 2-3 days check to see if the rest worked by pulling out a sample and doing the test and then lager it. My yeast according to wyeast labs said it produces low diacetyl and low sulfur aroma.. Don't know if that changes anything or not. Also should I do a secondary fermentation? For 1-3 weeks, i would do to 2 to be safe, at 39-41 degrees and then lager it?

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Old 05-09-2013, 05:03 PM   #5
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I was planning on fermenting for 3 weeks so.. Basically you think I should ferment for 3 weeks then bring it up to 65 degrees and hold there for 2-3 days check to see if the rest worked by pulling out a sample and doing the test and then lager it. My yeast according to wyeast labs said it produces low diacetyl and low sulfur aroma.. Don't know if that changes anything or not. Also should I do a secondary fermentation? For 1-3 weeks, i would do to 2 to be safe, at 39-41 degrees and then lager it?
I'd suggest bringing the beer up to diacetyl rest temperatures when the beer is 75% of the way to FG. Often, that's at about 1.020 or so, depending on the beer.

You want to do the rest while the yeast are still active, but winding down the bulk of fermentation. If you've already had the beer in the fermenter for 2 weeks, it's more than time to do the diacetyl rest. You may very well be able to skip the diacetyl rest with that yeast strain, assuming you pitched a big enough starter at a cool temperature.

I always rack before lagering, after the diacetyl rest. Once the beer is finished, and the diacetyl rest period is over, I rack the beer and begin lager.
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Old 05-09-2013, 05:16 PM   #6
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For my Kolsch I did it at two weeks.

  • I left it out for a couple days, it started bubbling when it warms up and the CO2 excapes.
  • Then I lager it for a few weeks...
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Old 05-09-2013, 07:37 PM   #7
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I pitched 250 ml of yeast that I grew it to that number using a stir plate. So.. I should have more then enough yeast. So skip it or do it? Just checked the gravity it's a little under 1030 right now.

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Old 05-09-2013, 07:47 PM   #8
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I pitched 250 ml of yeast that I grew it to that number using a stir plate. So.. I should have more then enough yeast. So skip it or do it? Just checked the gravity it's a little under 1030 right now.
Where did you start for an OG? To be at 1.030 after two weeks is a pretty slow fermentation, unless it's a really big beer that is supposed to finish high. My lagers are usually in the fermenter 7-10 days before the diacetyl rest.

I'd do the diacetyl rest when the beer is 75% of the way to FG, unless you absolutely don't want to. There is no disadvantage to doing one, even if it isn't strictly necessary. If you're an expert at detecting diacetyl and don't taste any, or don't find any in a test, then it could be skipped- but it never hurts to do one.
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Old 05-10-2013, 05:21 AM   #9
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My og was 1067 so i think it's doing pretty good... Should I let it ferment longer you think?

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Old 05-10-2013, 02:09 PM   #10
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Marking this thread for reference. I've made my first noticably diacetyl beer.

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