Author Topic: Terminating Fermentation Before Terminal Gravity  (Read 1003 times)

Offline UnequivocalBrewing

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Terminating Fermentation Before Terminal Gravity
« on: April 11, 2017, 05:35:26 PM »
Do people have opinions on stopping a fermentation before hitting terminal gravity?  Say for example you expected a beer to land at 1.014 but it looks like it's going to head more to like 1.011...would you cold crash prematurely at 1.014? 

It doesn't seem, on the surface, there is anything wrong with doing this but wanted to see if there were any off flavors this could create?  How much of the beer character happens toward the end of terminal gravity when yeast is "cleaning up"?

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #1 on: April 11, 2017, 05:50:55 PM »
Nope.  It won't work anyway.  Even cold the beer will keep slowly fermenting.  And I generally don't worry about 3 points FG difference.

It is a mistake to think that beer "cleans up" at the end of fermentation.  It happens all the way through and should be done by the time fermentables are gone.  Here's how John Palmer explains it....

"Essentially it is this:

100-150 years ago, fermentation was open, followed by maturation in a wooden cask. The beer was prone to contamination. This could be mitigated by heavy hopping and long warm maturation to wait for the bitterness to die down, or by long cold maturation (lagering) to use temperature to keep the contamination down.

Yeast have 3 phases in their life cycle: Adaptation, High Growth, and Stationary. (See Yeast by CW and Jamil) They do not have a maturation phase where they clean up byproducts. Adaptation phase is where they take in oxygen and build sterols and other lipids, assess the sugar composition and build enzymes, etc. Once those activities are done, they start the High Growth Phase, eating and reproducing. The number of cell divisions is limited by their lipid reserves they made during Adaptation. These reserves are shared with each daughter cell. When those lipid reserves are exhausted, the cell stops reproducing. In addition, when those reserves are exhausted, the cell is old and cannot eat or excrete waste efficiently across it’s cell membrane. A yeast cell typically can reproduce about 4 times during a typical fermentation, after that it is old and tired and tends to enter Stationary phase where it shuts down most of its metabolism and flocculates, waiting for the next batch of aerated wort. Stationary phase is essentially an inactivity phase, resting on the bottom.

Like I said, no conditioning phase as far as the yeast are concerned. Byproducts can be consumed at any point during the high growth phase, but they are a lower energy source than sugar, so guess what? Byproducts are not a biological priority. The brewer therefore needs to plan his pitching rate and fermentation conditions such that the yeast run out of fermentable wort sugar before their lipid reserves are exhausted and they go into stationary phase. Now you have a majority of vigorous yeast that have only undergone 2 reproductions (for example), the sugar is gone, and they are still hungry, so they turn to acetaldehyde and diacetyl as alternate energy sources and maturate the beer. You can help this by doing a diacetyl rest by raising the temperature a few degrees after the first half of fermentation, to keep the yeast active and eating. Where in the fermentation? after the first half, 2/3 to 3/4, when most of the attenuation has occured and raising the temperature is not going to cause rampant growth and the off-flavors associated with it. "
« Last Edit: April 11, 2017, 05:52:38 PM by denny »
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Offline UnequivocalBrewing

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #2 on: April 11, 2017, 07:16:48 PM »
Thanks for the info Denny.  I think you answered my question with the Palmer documentation.

However, I'm not sure I agree that it won't stop fermentation.  I take gravity samples out of my conical throughout primary fermentation.  I take the reading and then I chill it down in the fridge to drop the yeast out to see how aroma and taste are progressing.  Yeast drops out so fast and becomes inactive at fridge temperatures from what I can see.  Granted I haven't measured gravity before and after but there is no signs of continued fermentation.  Now a conical with 10 gallons takes a lot longer to hit that fridge temp but I'm guessing the same phenomenon happens.


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Re: Terminating Fermentation Before Terminal Gravity
« Reply #3 on: April 11, 2017, 07:39:41 PM »
Thanks for the info Denny.  I think you answered my question with the Palmer documentation.

However, I'm not sure I agree that it won't stop fermentation.  I take gravity samples out of my conical throughout primary fermentation.  I take the reading and then I chill it down in the fridge to drop the yeast out to see how aroma and taste are progressing.  Yeast drops out so fast and becomes inactive at fridge temperatures from what I can see.  Granted I haven't measured gravity before and after but there is no signs of continued fermentation.  Now a conical with 10 gallons takes a lot longer to hit that fridge temp but I'm guessing the same phenomenon happens.

I can pretty much guarantee you that the yeast is continuing to work.  Through sad experience.
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Offline dmtaylor

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #4 on: April 11, 2017, 08:37:01 PM »
Gelatin, cold, and extreme laziness can stall a fermentation permanently and on purpose, if you want.  I do this with my ciders.  However, be warned: it does require extreme laziness.  I mean to say, patience.  Patience.

On the other hand, results are difficult to predict.  Denny's theory is right more than half the time.  The other half of the time, you do run some risk of oxidation, lack of carbonation, possible contamination or other calamities, unless doing force carbonation.

Then there is the sorbate and sulfite option.  Don't do that, at least not with beer.  I currently have an IPA with zero carbonation because of that huge blunder.  Call it an "experiment".  Well it worked, if you enjoy flat beer.  It was bottled and primed like "normal" except for whatever reason, I added sorbate.  After a month, it's clear the yeast is pretty much dead, maybe just the slightest petillance, and huge diacetyl bomb.  Oops.  Won't be making that mistake a second time.
« Last Edit: April 11, 2017, 08:43:48 PM by dmtaylor »
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Offline erockrph

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #5 on: April 12, 2017, 02:56:10 PM »
I think Denny and Dave are both right to some extent here. Yeast will continue to ferment slowly before they peter out, but they eventually will. I think the issue is that you can't instantly halt a fermentation at a particular SG just by cold crashing. If you wanted to prematurely arrest fermentation at 1.014, you would have to start taking measures before it gets to that point. The only way to completely arrest fermentation instantly would be to pasteurize (either chemically or by heat) or via sterile filtration.

In general, I just think it's a bad idea with beer. If you have a beer end up at 1.011 and really want it at 1.014, add some maltodextrin.
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Offline HoosierBrew

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #6 on: April 12, 2017, 03:11:10 PM »
I think Denny and Dave are both right to some extent here. Yeast will continue to ferment slowly before they peter out, but they eventually will. I think the issue is that you can't instantly halt a fermentation at a particular SG just by cold crashing. If you wanted to prematurely arrest fermentation at 1.014, you would have to start taking measures before it gets to that point. The only way to completely arrest fermentation instantly would be to pasteurize (either chemically or by heat) or via sterile filtration.

In general, I just think it's a bad idea with beer. If you have a beer end up at 1.011 and really want it at 1.014, add some maltodextrin.




I agree. It's a bad idea, especially for bottlers obviously. Modifying recipe and/or mash temps until you're fermented out at your target FG is a lot more desireable IMO.
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Re: Terminating Fermentation Before Terminal Gravity
« Reply #7 on: April 12, 2017, 04:17:26 PM »
I think Denny and Dave are both right to some extent here. Yeast will continue to ferment slowly before they peter out, but they eventually will. I think the issue is that you can't instantly halt a fermentation at a particular SG just by cold crashing. If you wanted to prematurely arrest fermentation at 1.014, you would have to start taking measures before it gets to that point. The only way to completely arrest fermentation instantly would be to pasteurize (either chemically or by heat) or via sterile filtration.

In general, I just think it's a bad idea with beer. If you have a beer end up at 1.011 and really want it at 1.014, add some maltodextrin.

I have first hand experience that it happens.  Back in the days when I started brewing, the SOP for saving yeast was to put it in a capped bottle.  I had to pick glass shards out of my fridge a couple times after doing that.
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Offline UnequivocalBrewing

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #8 on: April 17, 2017, 05:02:17 PM »
The last IPA I brewed had a large 5-minute boil addition, a large flameout addition, and while I was cooling the wort I added a bit more hops at the 165F range.  The beer had a terrific aroma of bright tropical fruit and citrus.  Just what you would expect from Citra, Centennial, and Mosaic.

Primary fermentation seemed to be healthy and the aroma on the beer was incredible as I checked it throughout.  I did a 4 oz dry hop at high krausen.  The beer got down to about 1.012 from 1.060 in about 6-7 days.  I never measured to see if it was stable but I dry hopped with some fermentation activity in the conical.  I added another 8oz of dry hop waited a day and dropped to 60F.  After a day and a half at that temp I crashed it to 40F.  I kegged using a closed transfer with CO2.

The aroma went from this bright fruity citrusy aroma that was just so pleasant to now it has this aroma that is hard to describe.  You can smell some of the citrus but there is this piercing solvent-like thing coming through that overpowers any pleasant aroma.  I get some solvent-like aroma and some medicinal type aroma off it.  I can't tell if my hopping rates are too high (12 oz dry hop in 10.5 gallons) or if I'm having fermentation issues?  This beer was incredibly pleasant and I started to notice the change right around 2 days into my second dry hop when the beer temp went to 60F. 

Any thoughts?

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #9 on: April 17, 2017, 05:09:29 PM »
What was your fermentation temp?
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Offline UnequivocalBrewing

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #10 on: April 17, 2017, 05:17:00 PM »
I pitched at 63F and held that temp for about 75% of the fermentation before raising it up to 68F. 

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #11 on: April 17, 2017, 05:20:53 PM »
I pitched at 63F and held that temp for about 75% of the fermentation before raising it up to 68F.

OK, that doesn't sound like the problem then.  I get undesirable characteristics by dry hopping on the yeast, but not what you mention.
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Offline UnequivocalBrewing

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #12 on: April 17, 2017, 05:23:42 PM »
I didn't have an issue until about 2 days into dry hopping.  Right around the time I dropped the temp to 60F.  Could I have put strain on the yeast during the end of fermentation?

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Re: Terminating Fermentation Before Terminal Gravity
« Reply #13 on: April 17, 2017, 06:00:46 PM »
I didn't have an issue until about 2 days into dry hopping.  Right around the time I dropped the temp to 60F.  Could I have put strain on the yeast during the end of fermentation?

Nope, especially with that little drop.  I generally do 63 for about 4 days, 70 for 3 days, then crash to 30 without problems.  I think it's more likely you're tasting biotransformation of the hops, although I've never heard it described quite like that.
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