So I made my Czech Pils 3 weeks ago. I, for whatever reason/excuse didn’t initiate a D rest. The fermenter stayed at 52* for the entire time until it was time to cold crash.
To my point, I did not perceive any diacetyl at all. Is it possible that I don’t have the ability to detect it? Was it even present? Doing a quick internet search it is said that it only takes 0.001 parts per billion to taste or smell. I use 34/70 for this recipe and maybe that yeast isn’t a big producer of it? ( I will search later).
I always do a D rest because that is what I have learned to do and it is an easy step if you have the equipment to do so and only adds a few days to the fermentation schedule.
Although I will continue to do a D rest, is it absolutely necessary?
It IS possible that a person cannot detect diacetyl; some folks are blind/insensitive to it’s expression.
It was almost certainly present during fermentation at some point, to some level - regardless of yeast strain (ale or lager). It’s a natural production of brewer’s yeast which is then up-taken at the end of fermentation at varying speeds and to varying degrees.
My experience with the 34/70 strain variants is that they are not big producers of diacetyl and ARE good, quick up-takers of D if allowed to remain some time at fermentation temperatures once reaching final gravity - given sufficient, healthy pitches of yeast. I rarely elevate my lagers to D-rest temps when using german lager strains; true czech strains, on the other hand, I give a solid D-rest.
I seldom do a d rest. Maybe one batch out of maybe 20. If I don’t taste diacetyl, I don’t bother. While it’s possible you can’t detect it, it may be more likekky you don’t have it.
Some people I know never do one but they leave the beer at fermentation temp for a couple weeks after fermentation and before dropping temp… maybe the time has something to do with it and not just the temp.
This is an interesting subject. A couple years ago, I attended a “off flavor” sensory perception class at my LHBS. The class, was hosted by a representative from White Labs (if memory serves). In the class, we had individual tastings with roughly 6-7 different “off-flavors”, with a different off-flavor in each beer. Of the various tastings, I could only detect a couple off-flavors. So, I agree, some people don’t have the sensory capability to detect some off flavors. I guess I would make a bad Beer Judge — :-\
I almost always to a D-rest simply out of habit rather than necessity.
Being blind to diacetyl can be overcome by training and using different techniques, such as a quick covered dish of the beer in a microwave for a half minute - opening the dish after heating will often expose diacetyl by smell (buttery aroma); also perception by mouthfeel is possible - often a slickness to the beer.
That said, I don’t usually do a diacetyl rest, because the yeast will cure it with time and I rarely am in that big of a hurry….
That doesn’t mean you would be a bad judge. Honestly a lot of picking out off flavors is practice. I remember the first off flavor testing I did, I could not find “green apple”… I knew something was off… Maybe because they told me but I wouldn’t have described it like that. After more practice, it got easier to pull out and different styles of beer can present the same off flavor in a different way/mask it more, so it comes down to digging, playing, and learning how to describe what you’re tasting.
My normal fermentation routine is to raise the temp at the end to hurry things alone – usually after about 72 hours. That is both ales and lagers. It’s not a bad habit to get into. Of course sometimes I either forget or I am fermenting ambient basement temps and in those cases I just give it some extra time since yeast will clean up the diacetyl in almost every case (except infection).
Alpha acetolactate is the precursor to diacetyl and you can’t taste it but it can turn into diacetyl if oxidation or warm temps are introduced during packaging. Yeast will usually clean up alpha acetolactate during the d-rest but if you are unsure you can always heat a sample of your beer to about 140° (I like to use a sous vide in a glass jar for about 20 minutes) and cool it down to serving temps and smell/taste it. If you smell/taste diacetyl let the beer sit on the yeast for another few days. IME that almost always takes care of diacetyl.
If IIRC yeast can’t absorb the Alpha Acetolactate. It has to be oxidized to form Diacetyl which can be readily absorbed by the yeast and converted. Both the oxidation and absorption by the yeast happen faster at higher temperatures.
“…until it was time to cold crash.” If that means immediately after a few days of stabile hydro readings, then maybe you’re at risk for diacetyl. But if you can’t detect it, then no problem, especially if you are the only consumer. But if “time to cold crash” means a week or more after stabile readings, then I’d say you’re probably not at risk.
In that case then perhaps the warmer temps of a d-rest are more important. Or if you keep the beer cold and low DO pick up on packaging it isn’t going to be a problem.
A dedicated d-rest is simply an insurance policy. In a normal, healthy fermentation, ale or lager, the yeast take care of it without needing to be warmed up. Yeah the warming can speed things up, though. Minor correction, and sorry to be pedantic here: the taste threshold is ~10-50 parts per billion, not 0.001 ppb, which would be 1 part per trillion.
Is it possible that the “tradition” of a diacetyl rest (can’t bring myself to type “D rest” over and over… seems immature) came from either:
high speed industrial brewing where beer needed to be produced rapidly for sale and needed to be cleaned up on a very short time frame, or
historical brewing methods included it because of lower quality yeasts/ lower pitching rates?
Personally, I’ve had yeast clean up a beer during a diacetyl rest AND/OR clean up after a longer time in the bottle. Seemed to get the same result with either a temperature spike or just more patience.
Since I started pitching a tonne of yeast slightly below fermentation temps ( 6-7c ) and immediately bringing the beer up to fermentation temp ( 8-10c ) after pitching, ive never needed to do a D rest. I always bring lagers up to 12c after about a week, then up to 15c for another week. Then just keg. They’re clear and clean tasting.
