Diacetyl Rest in Lager Brewing: Do you do it or not?

[Finn]

Hey folks, I'm seeing/hearing from lots of reputable lager brewers that a d-rest is unnecessary if your fermentation is conducted properly, i.e., pitch/ferment cool (50ish F), and give it plenty of time.

I'm gearing up to do lagers in the brewery, and am trying to understand the pros and cons of D rest better. Can a D rest hurt anything? I see it would be a time sink if you are moving temperatures slowly up and way back down again to lagering temps. Is that the reason these lager brewers don't bother with it? To save time, maybe?

Any insights much appreciated.

[dick murton]

The traditional lager fermentation profile is to run at a top heat of somewhere between around 9 and 12 deg C depending on the yeast strain and flavours desired, and then cool down slowly over a period of days or even weeks to around zero C and then store for a further period at zero or colder - but this latter storage is largely for yeast and protein precipitation rather than flavour changes, though of course the flavour does change slowly. Because lager yeasts retain a degree of activity at these low temperatures during the cooling period, the diacetyl is mopped up and changed to less flavoursome substances, amongst other perhaps more subtle flavour changes.

The more modern take on this is that slow cooling and cold maturation costs too much money in tank space, refrigeration and as used to be the case in the UK up until 1993, cost an arm and a leg in interest payments on the duty paid on the beer - before it was sold. Through research, and perhaps even accidents in the production process, it was discovered that allowing the temperature to rise naturally towards the end of fermentation gave a much faster diacetyl removal time. So it has evolved that it is now common to ferment with traditional lager yeasts at let's say 9 deg C, and part way through the fermentation, turn off the cooling, and allow the temperature to naturally rise due to heat of fermentation up to circa 13 / 14 C - again, every brewer and beer will have different temperature profiles. Hold it at the top diacetyl rest temperature for a period until the diacetyl levels have been reduced acceptably, and then crash cool for yeast removal (if not already done) and for cold conditioning, primarily yeast & protein removal.

Which to do - up to you really. Do you have the capacity and accurate control to be able to mature in the traditional manner, say six weeks or longer, or do you need the throughput, and my guess is the throughput comes first if you have not set out to produce lagers in this manner and equipped the brewery as such.

A couple of other points.

Not all lager yeasts work well with low temperature fermentation, and will virtually stall - so required temperatures of circa 18 deg C, in which case you don't need to allow a temperature rise, but might want to hold at that top heat temperature for a day or two after the fermentation is finished - again, totally yeast and flavour dependent.

And second - some lager yeasts will only work cold, and if allowed to ferment or rise up to or above about 15 deg C (my experience, so other's experiences may differ) you may well horrifically strong sulphury notes. How do you tell beforehand? - no idea apart from checking with your yeast supplier.

Having said that flavours don't change much if stored at zero or thereabouts, I started work at one brewery whose beers I used to drink fairly regularly, and discovered some had been in store at minus 1 for over six months - I could have drunk that tank dry myself if it were possible, it was so good.

[Finn]

Dick, thank you very much for the knowledgeable input.

I'm more gearing up to gear up for lager brewing at this point, so I'm getting my initial plans for technique ahead of time, I've done some small test batches at home to get a feel for the yeast strains I may want to use. No new brewhouse yet.

To your point about some yeasts only work well cold: That hits on much of why I posted this post, I'm happy to do a quick D-rest if it doesn't negatively affect my finished beer flavor, but if there's a risk with some strains then I'll just take my time at cold temps.

I've been mainly focusing on the 34/70 strain, and the Augustiner strain....I haven't been able to find out if they are "cold only" strains or not, although I see plenty of people doing D rests with those strains so I assume 34/70 and Augustiner are ok to do a warm rest with.

This all leads me to another question I've had related to all this: Could a diacetyl rest UNDO any of my cold fermented (9-12) goodness?
I understand there's not always hard and fast answers to these questions, I'm just new to lager brewing (so far only at home) and have so many questions.

Thanks for sharing your knowledge, much appreciated!

[dick murton]

"Could a diacetyl rest UNDO any of my cold fermented (9-12) goodness?" Well all I can say is that having brewed a number of different lagers with a "top heat" of 9 or 10 C, but with a D rest of 13 C (nominal - 72 hours at 13, add 24 hours for every 0.5 deg C below that, but don't shorten if above 13 C) that the beers were OK, but since I never brewed them the long slow cold maturation way as well, I couldn't compare results to know if one was better than the other. But I bet if you talked to most German and Czech brewers they would insist long, slow and cold is the only way to go - but then they often insist on decoction mashes are the only true brewhouse methodology, and this is not necessary in mine, or many other brewers, even those who have brewed regularly on Germany or Czechoslovakia (or the devolved states). The only way in my opinion is to try both methods, see if you, and more importantly your customers prefer one version, and are prepared to cough up the price you need to charge, and then stick to the preferred methodology. If you do a higher temperature D rest, then having really good cold storage immediately afterwards - minus 1C for a few days is absolutely essential as you don't have the luxury of weeks of slow protein haze formation and settlement.

[Finn]

Good thoughts, great to hear what more experienced brewers than I have tried/not tried, and how it all worked out.

I agree with the takeaway, you just have to try it both ways (or more) and see if it makes the difference you want.