What is benefit of slow temperature ramp down in fully attenuated and "rested" lager?

[Dland]

This is kind of related to another recent thread I started, but probably more universal question.

I currently slowly ramp down my lagers after D rest before cold crashing. Mainly do this because it is "generally recommended practice", and I have the set up to do so.

But discussions of yeast process and attenuation have me wondering what is the benefit of slow ramp down if yeast have already fully converted wort into beer, and unwanted compounds have already been worked off in diacetyl rest. We are talking generally at least 3 weeks since brewing at least anyway, so has not been rushed.

There have been times I did cold crash without much ramp down, and I'm not sure there was much difference in final outcome.

 

[day_trippr]

Related discussion here: https://www.homebrewtalk.com/forum/threads/lager-crash-cool-vs-gentle-cooling.406982/

While I'm inclined to go with the rationale that a solid D-rest may preclude the need for a slow cold ramp, I've yet to adopt that rationale and still do a 5°F/day slope down to ~34°F (basically, a week), keg a few days/week later, then cold-condition for at least three weeks while carbonating.

No idea if that's better or not, force of habit, really...

Cheers!

 

[ba-brewer]

On one of the brewing with style shows they discussed this, Tasty does a fast cold crash and Jamil does a slow crash. Jamil's comment was something like it depends on if you think the yeast is still working.

My lagers are starting to drop clear in 8 to 10day which would make me believe the yeast is done, so no need to slow crash.

edit: I don't cold crash in a formal sense, I transfer to a keg in 8 to 10 day and put in the cooler to carb and condition. There is normally still some yeast in suspension.

 

[McKnuckle]

The rationale for a slow temp drop is related to not shocking the yeast, which might cause them to become dormant. While that sounds good if you're looking to clarify the lager, in reality the lagering period is beneficial partly because of residual yeast activity, which further works its magic on compounds in the beer. Just because the beer is fully attenuated, that doesn't make it time to remove the yeast completely.

 

[Dland]

Thanks for the replies. Along with the thread day tripper linked, looks like we have a "definite maybe" or "it depends".

More specific questions come to mind;

Does yeast actually release off flavor compounds as a result of fast temperature drop?

Does the yeast do any meaningful metabolization after full attenuation and D rest?

Does the residual yeast left in bottom of crashed keg (or bottle) do anything to beer flavor after cold crash and during cold lagering period? If so, is it more likely to be more active if it was cooled slowly than crashed fast?

I guess I will continue to ramp down, at least some, when convenient. During high lager production times, I get low on temp control capacity.

Seems like an aura of craft, rumor and "how it is done" will continue to prevail over hard science in home brewing to some degree anyway. In this case, the practice in question is not that much trouble to implement(for me anyway), so on it goes.

If anyone making lager does not have capacity to "ramp down" slowly to crash, I'd advise them not to sweat it too much.

 

[mongoose33]

Curious to see what resolution comes to fruition from this, if anything.

I'm also struck by this thought as I read this admittedly short thread: how does the beer taste?

And struck by a desire to do an experiment comparing the two. I only have one conical but I could do a 10-gallon batch, and after D-rest rack 5 gallons off and immediately crash it, while controlling the temp drop on the conical. Problem is the conical would still be on the yeast, not so with the crashed one.

I still have a couple plastic fermenters and two ferm chambers.....thinking....thinking....

******

This also reminds me of a story: a new resident of the neighborhood moved in, only to discover his next-door neighbor would step onto his back porch at 6am each day and screech at the top of his lungs. Naturally this was disturbing.

After about 4 days of this, new resident approached the screecher and asked him why he did that. Screecher replied "It keeps the lions away." New resident said "But we don't have any lions around here" to which Screecher replied "See? It works!"

That came to mind when thinking about whether a slow crash has any positive effect....maybe we're just shouting to keep the lions away.....

 

[Vale71]

Does yeast actually release off flavor compounds as a result of fast temperature drop?

Not necessarily directly linked to off flavors per se but they can release enzymes that can be detrimental for beer stability affecting for example head retention.

Does the yeast do any meaningful metabolization after full attenuation and D rest?

Yes it does, especially for lagers. For example in a traditional lageer fermentation diacetyl cleanup could take several weeks. Having the yeast go dormant because of thermal shocking could turn this into a critical situation.

Does the residual yeast left in bottom of crashed keg (or bottle) do anything to beer flavor after cold crash and during cold lagering period? If so, is it more likely to be more active if it was cooled slowly than crashed fast?

No, yeast needs to be in direct contact with wort to metabolize its constituent substances. Yeast that has dropped to the bottom of any vessel cannot do that any more. What it can still do however is autolyse and release undesirable substances into the beer. In this regard this would be the only advantage of rapidly cooling to lagering temperature as this would delay autolysis. Of course removing the yeast in a timely fashion through a dump valve is still the best option regardless of temperature profile.

 

[ba-brewer]

There is a graphic figure in the middle of the page with various lager fermentation schemes, A few show reduction of diacetyl even after the beer is brought to conditioning temp.
http://www.braukaiser.com/wiki/index.php?title=Fermenting_Lagers

 

[mediant]

This excerpt from "Handbook of Brewing" by Graham G. Stewart et al. may give you some answers:

15.3.3 Lagering without Secondary Fermentation

Historically, beers using lagering employed shallow, open fermentation vessels for the primary fermentation stage but closed vessels for secondary fermentation in order to maximize carbonation. Modern equipment with refrigeration, carbonation, filtration, and so on obviates the need for secondary fermentation and a long, cold storage period. Modern brewing practice employs shortened fermentation and lagering times and uses rapid cooling after fermentation to stimulate yeast settling. Techniques for rapid fermentation accelerate the utilization of wort sugars. If the wort is fully attenuated during primary fermentation, there is no need for secondary fermentation per se, and the aging process is principally focused on flavor maturation and yeast settling.

As described earlier, one of the more important classes of compounds involved in flavor maturation are the VDKs. Because the rate of VDK precursor conversion is temperature dependent, elevating the temperature (also termed a “free rise”) can be used to hasten the conversion. Short, warm lagering has proven quite effective, with minimal deleterious effects on beer quality. This lagering should be accomplished in the presence of yeast by extending the residence time in the fermentation vessel at the upper temperature limit after the wort is fully attenuated. If there is a lack of sufficient suspended yeast, wort recirculation or “rousing” with a CO2 purge can help.

With modern equipment, the use of separate vessels is unnecessary; and some unit operations may be combined in a vertical fermenter unitank operation. For example, after a predetermined attenuation limit has been reached, yeast (for reuse) can be removed from the bottom cone and the beer cooled for lagering. Periodic removal of more yeast may be beneficial during the lagering phase to prevent off-flavor development. There are compelling economic advantages for combining fermentation and aging in one tank.30,31 Other advantages of this concept30 are (a) fewer microbiological and foam retention problems because of reduced transfers; (b) more efficient yeast collection; (c) improved control of beer CO2 levels, with the possibility of eliminating carbonation; and (d) better opportunities for automation. However, a major disadvantage of the unitank approach relates to the need for longer residence time in the single vessel due to the increased time required to cool beer to 0°C, or lower, within a single vessel, compared with the rapid chilling available through a plate heat exchanger on transfer from fermenter to a maturation vessel, without the risk of freezing the beer.