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Beersmith's secondary fermentation for lager: just three days?

wolf

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I generally rely on primary fermentation only for my ales (that is, I don't rack to secondary after a few days but let it ferment completely in the primary) because my ales sit on the yeast cake for a month at most. However, if I were to use primary fermentation only for lagers, the beer would be exposed to the sediment for a long time so secondary fermentation would seem advisable.

Looking at Beersmith's fermentation profile for lagers, it seems that primary fermentation lasts a little less than two weeks, which seems reasonable enough: the lower temperature causes slower fermentation and in my experience, gravity measurements by the end of this time indicate that primary fermentation is indeed tapering off.

But, as far as I can tell, Beersmith considers the diacetyl rest to be secondary, thus having secondary fermentation take only two or three days. In ales, the secondary fermentation generally takes a little less than two weeks, so for lagers I'd expect it to be no less than a month given the slower fermentation.

So it seems I missed something. Does the diacetyl rest really cause the fermentation to complete entirely--thus making lagers ferment just as fast as ales? ... Or what did I miss?
 

brewfun

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wolf said:
But, as far as I can tell, Beersmith considers the diacetyl rest to be secondary, thus having secondary fermentation take only two or three days. In ales, the secondary fermentation generally takes a little less than two weeks, so for lagers I'd expect it to be no less than a month given the slower fermentation.

So it seems I missed something. Does the diacetyl rest really cause the fermentation to complete entirely--thus making lagers ferment just as fast as ales? ... Or what did I miss?

With BeerSmith 2.2, fermentation is represented in a maximum of three stages, no matter what the style. After that, it's bottle aged. This means that you can graph a fermentation in only 6 points, which usually isn't enough detail for a complex profile.

A three day diacetyl rest does cause the yeast to dry the beer out and complete sugar consumption. Diacetyl is typically consumed in just a day, but letting the rest last longer accomplishes another needed milestone. What's missing is maturity (mostly sulfur reduction) and that's what lagering is all about. Depending on the wort and the yeast, maturity can happen in a couple of weeks or can take months.
 

wolf

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I agree with your explanation but I still think I'm missing something important. Let me try to explain how I see it (let's put aside the question of the subsequent lagering for now):

A typical ale ferments in primary for about four or five days until about 75% or so of the wort has fermented. It is then racked to secondary where it ferments for about another ten days using yeast that is still suspended in the wort. (In simple terms, that is. Mileage may vary.)

In contrast, a lager sits in primary for about ten days because the fermentation is slower at lower temperatures. Then when the temperature is raised for the diacetyl rest, the fermentation completes entirely in a day or two. So far we agree... but this is when I suddenly begin to wonder: if the beer is racked to secondary after the diacetyl rest then there's no fermentation going on in the secondary phase. Doesn't this imply that "secondary" means something quite different for a lager than it does for an ale?
 

Oginme

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While active fermentation may be done after the diacetyl rest, the yeast will still be active in cleaning up some of the by-products they release during active fermentation. 
 

brewfun

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wolf said:
but this is when I suddenly begin to wonder: if the beer is racked to secondary after the diacetyl rest then there's no fermentation going on in the secondary phase. Doesn't this imply that "secondary" means something quite different for a lager than it does for an ale?

Except that there isn't "no fermentation going on."

Primary: Alcohol production to at least 90%, often greater.

Secondary: The reduction by yeast of byproducts which may or may not be flavor active.

Lagering: Extended storage to allow continued reduction of byproducts to a flavor acceptable level.

So, primary encompasses yeast growth, high and low krausen all the way though acetaldehyde elimination. That seems to imply that primary overlaps secondary, except that acetaldehyde is converted to ethanol.

Diacetyl reduction means converting the tasteless but unstable precurser, Alpha Acetolactate, into more stable  2, 3-butanediol, which is also tasteless. By tasteless, I mean the human noses aren't sensitive to it, but your dog may have a different opinion. Since the reduction of Alpha Acetolactate is part of the normal yeast pathway, but doesn't involve alcohol, we can call this "secondary" fermentation.

"Secondary" doesn't mean that all alcohol production has ceased, only that most of it has and the yeast continues to metabolize.

The fact is that we expect lagers to have far more reduced side flavors than ales. Given time, even ale yeast will reduce many side flavors we thing of as just part of its profile. "Lagers," as a recipe, can be made swiftly, with either ale or lager yeast, yet the drinker is less likely to accept the side flavors.
 

wolf

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Thanks, brewfun. That makes much more sense to me. The simpler explanations that fermentation completes during the diacetyl rest didn't seem right to me.

Another question, though: as a bottom-fermenting yeast, doesn't lager yeast sink to the bottom of the wort rather than staying suspended in the liquid? That is, how come there's a sufficient amount of yeast in the wort for completing the fermentation when the wort is racked to secondary?

(I expect the answer to be "certainly yes, there's enough yeast" but it seems to me that top-fermenting yeast is more likely to be suspended in the wort.)
 

brewfun

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wolf said:
Another question, though: as a bottom-fermenting yeast, doesn't lager yeast sink to the bottom of the wort rather than staying suspended in the liquid?

...but it seems to me that top-fermenting yeast is more likely to be suspended in the wort.

Nope.

Yeast is suspended all through the wort in both cases. the more accurate term would be "Top Cropping" or "Bottom Cropping" because that's where you'll classically find the yeast right after primary.

But lo and behold, modern yeast pretty much all falls to the bottom for cropping. So, there goes that.

We are beholden to arcane terms that don't match modern reality. In that way, we brewers very clearly have a language all our own that must be comprehended in order to communicate.
 

wolf

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brewfun said:
We are beholden to arcane terms that don't match modern reality.

Ha ha. Yes, there are a few terms that seem misleading or somewhat dated, but for the most part I think we're actually not particularly jargon-infested compared with other crafts.

Most of the jargon probably doesn't even matter until we start to think about what is going on. For example, I've brewed only one lager before in a "don't think, just follow instructions" mindset, and it came out excellent and will certainly be repeated. It's just that I suddenly began to think a little about the lager fermentation compared with the ales I'm used to brewing.
 
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