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When to do a diacetyl rest?

Hello i have a german pils fermenting an it’s been about 2 week’s so far… Here the problem i have one book telling me to wait ontel the last 2/3 i have others saying wait at the end of fermention. An then i hear that if you pitch cold at 44f or so an let rise too 50f an hold at 50f for like 4 weeks u don’t need to do a diacetyl rest at all???..

If you taste diacrtyl you need to do it If not, don’t.

I often do it after the beer has attenuated 75% of what it should. Bringing up the temp slowly allows for the yeast to finish up and clean up.

You can also do a forced diacetyl test, as often times during the fermentation process you cannot pick it out, as only the precursor (alpha-acetolactate) is evident, and is imperceptible.

http://www.winning-homebrew.com/diacetyl-test.html

I tried this once on an Okfest and its pretty easy. May be worth having someone around with a decent palette that doesn’t know he/she is looking for butterscotch, buttery flavors. I’d suggest a blind triangle tasting with both samples to see if your taster can pick out the different one.

If no butter in the oxidized sample, you can likely get away without a d-rest. However, I don’t think it ever hurts to raise the temp up a few degrees toward the end of the fermentation on just about any beer style, particularly lagers, to ensure full attenuation.

I make a lot of lagers and my gut tells me that it doesn’t really matter when you do it. My typical routine is to let primary fermentation run its course over 2-3 weeks. At that point I will take the primary out of the fridge (usually so I can put ANOTHER lager in there to ferment) and just leave it on my cool basement floor where the primary temp probably rises to 60° or so. I might leave that primary there for 2-3 days or maybe a week or so before I can transfer that beer out and either reuse the yeast or retire it. I do this on every batch regardless of which lager strain I’m using and I never have diacetyl. Good luck & cheers.

You need to taste the beer when it’s about 2/3 done. If it tastes buttery at all, do the rest at 2/3 done. If not, you can safely skip it. It is better not to wait for the yeast to all settle out and then do a rest because the yeasties are not very active at that point.

I don’t find that to be true and I would hate to see someone mucking around in the beer when it was 2/3rds of the way through fermenting. Let it run all the way through, take it out of the cold spot and let it settle into a 60° (or so) spot for a few days and feel free to rouse or swirl the primary a little bit to get the yeast back in suspension. Trust me, it works like a charm and you don’t risk contaminating your beer by checking it while it’s fermenting. This is all in the spirit of making the best beer possible and I have made hundreds of batches of lager beer. Keep us posted and cheers.

Ken, you may be right. I’m sure you’ve made more lagers than I have. That being said, I usually don’t get diacetyl anymore so I haven’t had to do a D rest for a while. Probably because I pitch the right amount of yeast now, and in the old days I didn’t.

The funny thing about d-rests is that I end up doing “extended d-rests” anyway because after one of my lagers comes out of primary, it ends up in secondary on the basement floor for awhile before it goes to the fridge because I just don’t have enough cold storage for all of my lagers to continuously stay cold. So they sit in secondary for 3-4 weeks, go to a keg, get cold and carbed and may sit for another 4-6 weeks at 35° which is when the lagering phase takes place. But all of the time before that could possibly be considered a d-rest. Anyone who makes lagers will eventually decide how they like to treat them. I do the d-rest on all lager strains simply because it’s easy and it fits in nicely with my processes. There are probably plenty of people who don’t do them and everything is fine. There are also people who like the “75% into fermentation” strategy (for d-rests) and it works out well also. Cheers.

EDIT: Pitching the right amount of yeast is big and for those who aren’t sure about it, check out one of the calculators for pitch rate for ales, lagers and the specifics of your batch. It is possible for homebrewers to overpitch.

I am making my first lager now. I fermented at 51 degrees. Sunday I took the carboy out of the freezer to start the d-rest. I was hoping my basement would be around 70 degrees, but it has been cool ant the carboy temperature is 67 degrees. Is this temperature OK for the d- rest? I was planning on giving it 5 days for the d-rest, racking to a secondary on Saturday. Then dropping the temperature to 35 degrees for the lagering phase. I was planning on kegging it after 6 weeks, then tapping it in September. Sound OK?

Looks AOK to me. Although I do my primary fermentation for lagers a little colder(45-50 usually). 67 for d-rest is a good temp, and 35 for lagering is perfect.

I’ve only done one lager so far and did just what Ken said. 2 week primary @ 49, took it out for 6 days @ 67, lagered @ 37 for 6+ weeks & bottled. After a month in bottle, turned out great with no weird flavors. Not sure if i needed the d-rest, but glad i did as it is a tasty sob! :slight_smile:

The other thing that occurs to me is that warming the lager up a little bit after primary is good for scrubbing out sulphur (if your lager strain created some) or any other weird flavor that might have developed during primary fermentation in the cold. I agree that 67° is just fine for the d-rest and I also agree that the primary temp could be a little cooler… my lager primary fridge is set to 47°. If you believe that primary fermentation can actually create heat and raise the temp 5° and that would put me at 52°. If that were true for your 51°, that would put you around 56°. Some lager strains are fine at that temp and for some it’s high or at the high end and I prefer to be at the low end. I happen to be drinking some of my Bordertown Mexican Dark Lager at the moment and it came out muy delicioso. Cheers Beerheads.

Thanks everyone for the useful help. The d-rest has been going on for three days so far. I noticed small bubbles breaking the surface once in a while. When I rack into the secondary on Saturday, and I begin the lager phase. Is it recommended to drop the temperature 2 degrees a day until I hit the desired lagering temperature? Or can I just set the external temp. controller to 34 degrees and place the carboy in the freezer at the same time?

Thanks
Brad

[quote=“Bier brauer”]Thanks everyone for the useful help. The d-rest has been going on for three days so far. I noticed small bubbles breaking the surface once in a while. When I rack into the secondary on Saturday, and I begin the lager phase. Is it recommended to drop the temperature 2 degrees a day until I hit the desired lagering temperature? Or can I just set the external temp. controller to 34 degrees and place the carboy in the freezer at the same time?

Thanks
Brad[/quote]
I have never had the patience to drop the temp 2° per day so I cannot say whether it’s a benefit or not. I bring my lagers from room temp-ish (60°) and they go down to 35° probably overnight and I am very happy with my results. Good luck with it.

[quote=“Ken Lenard”][quote=“Bier brauer”]Thanks everyone for the useful help. The d-rest has been going on for three days so far. I noticed small bubbles breaking the surface once in a while. When I rack into the secondary on Saturday, and I begin the lager phase. Is it recommended to drop the temperature 2 degrees a day until I hit the desired lagering temperature? Or can I just set the external temp. controller to 34 degrees and place the carboy in the freezer at the same time?

Thanks
Brad[/quote]
I have never had the patience to drop the temp 2° per day so I cannot say whether it’s a benefit or not. I bring my lagers from room temp-ish (60°) and they go down to 35° probably overnight and I am very happy with my results. Good luck with it.[/quote]

Thank you Ken. The way you do it seems like a plan to me. Do you think I should wait to see if those tiny bubbles stop before racking to the secondary? The yeast has to be somewhat active to be making these small bubbles.
Brad

The small bubbles can be misleading and it’s hard to know if this is active fermentation or CO2 escaping from under the yeast, both, etc. The best way to know is to take a gravity reading because there is no question once you take that measurement. To avoid that, to test my patience and to keep my otherwise lazy character intact, I typically go for 2-3 weeks in the fridge (more than enough) and then go another week or so at d-rest temps depending on what else is going on in life. That, to me, is more than enough time for the standard lager to ferment, d-rest and settle. How long has your beer been in primary? The small bubbles can be active fermentation brought on by the raising of the temperature and typically I don’t like to muck with the beer until it’s all quiet. If you take the hydro reading three days in a row and it’s the same, you’re gold. If not, wait.

The beer has been in the temp. controlled freezer at 51 degrees for two weeks. This past Sunday I started the d-rest at room temperature @ 67 degrees. I planned on racking to the secondary this Saturday. If it is ok to go longer I can certainly do that. Before the d-rest, I took a reading with the refractometer two times. The brix reading was about the same, it did drop just a little but according to the conversion table the gravity reading was the same. Maybe I’ll start another series of readings Saturday till Monday, if no change I will rack on Wed. because of the work schedule

If it was cold for 14 days and now d-resting for 4-5 days, you’re probably fine. It’s always safe to take a reading but if you’re going to a secondary, I’m sure that 18-19 days is fine for a 5% beer. Cheers.

Thanks Ken! Cheers to you also! :cheers:

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