Author Topic: What does it mean to let a fermentation free rise?  (Read 2921 times)

Offline brushvalleybrewer

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What does it mean to let a fermentation free rise?
« on: March 02, 2012, 04:51:26 AM »
I know that fermentation generates heat. I've demonstrated it to myself by measuring the temperature inside and outside an uncontrolled fermentation and seen as much as 8 °F difference. But I have also seen that in my 50 °F cellar, the beer in my carboy never gets above the temperature I have my set on my Johnson controlled FermWrap.

So when I see a recipe say, "Start fermentation at 64 °F and allow to free rise to 69 °F," and I have seen some professional brewers give this advice, what does it mean?

I mean, if the ambient temperature is 64 °F I can imagine one thing happening, but if the ambient temperature is 85 °F, it will be another, and if I control the temperature, well then I'm not exactly letting it free rise, am I?

So, what does it mean?
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Offline tygo

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Re: What does it mean to let a fermentation free rise?
« Reply #1 on: March 02, 2012, 04:54:10 AM »
I think it means just what you think.  Start it off at pitching temp and let it go where it will.  Obviously you'll have to take the ambient temp of where you're storing the fermenter into consideration when deciding if that's a good idea for the beer you're making. 
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Offline repo

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Re: What does it mean to let a fermentation free rise?
« Reply #2 on: March 02, 2012, 06:41:37 AM »
 
I know that fermentation generates heat. I've demonstrated it to myself by measuring the temperature inside and outside an uncontrolled fermentation and seen as much as 8 °F difference. But I have also seen that in my 50 °F cellar, the beer in my carboy never gets above the temperature I have my set on my Johnson controlled FermWrap.

So when I see a recipe say, "Start fermentation at 64 °F and allow to free rise to 69 °F," and I have seen some professional brewers give this advice, what does it mean?

I mean, if the ambient temperature is 64 °F I can imagine one thing happening, but if the ambient temperature is 85 °F, it will be another, and if I control the temperature, well then I'm not exactly letting it free rise, am I?

So, what does it mean?

Your controller is working so your beer temp doesn't rise above the set temp. It shuts off the heater.

Free rise - allow it to rise naturally without artificial means.  So by exothermic reation and/or by ambient temperature. This will occur slowly, which is the key.

At 64 ambient it wil not always get to 69, when it does use your heater to keep it there. At 85 ambient you will need some sort of cooling to keep it at 69.

Offline narvin

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Re: What does it mean to let a fermentation free rise?
« Reply #3 on: March 02, 2012, 07:00:09 AM »
Most breweries use cooling to maintain temperatures since the ambient is 65-75 depending on the time of year .  To free rise to 69, the set point is set at 69 and no external chillig is applied until it rises to that point.

Obviously this won't work in a 50 degree garage...
« Last Edit: March 02, 2012, 07:04:55 AM by narvin »
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Offline bluesman

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Re: What does it mean to let a fermentation free rise?
« Reply #4 on: March 02, 2012, 07:45:10 AM »
The fermentation temp is dependent upon a few factors. The OG of the beer and the AA% of the beer will determine the amount of work the yeast have to do, which in turn will create an exothermic condition in most cases. The amount of yeast and their health can also be a factor. The pitching temp as well as the ambient temp are a significant factor. All of these things come into play when trying to understand how the fermentation will behave.

A typical example: If you ferment 5 gal of a 60GU beer at 64F with 200B cells of an ale yeast in an ambient temp of 68F, there will likely be a temp rise of 4-6 degrees over the course of the fermentation (high krausen).
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Offline bo

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Re: What does it mean to let a fermentation free rise?
« Reply #5 on: March 02, 2012, 09:55:02 AM »
Why do I envision a bunch of homebrewers in a brewery, holding up cigarette lighters and yelling "Free Rise"?
« Last Edit: March 02, 2012, 09:56:35 AM by bo »

Offline tschmidlin

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Re: What does it mean to let a fermentation free rise?
« Reply #6 on: March 02, 2012, 05:03:08 PM »
In every case fermentation creates heat.  What you are seeing though, is that the speed the heat is generated makes a difference.  In your 50F example, heat is generated slowly enough that the ambient conditions keep up with it and the heat is removed - your fermwrap is even adding heat to keep it at the setpoint.  At higher temps the reaction goes faster and the ambient conditions are not sufficient to keep up, so you get a temperature rise above ambient/fermwrap.

Pro brewers advice is different though - they are fermenting much larger volumes of beer.  With the lower surface/volume ratio the heat won't be dumped as quickly so they will get a bigger temperature rise.

If I was letting a beer free rise, I would not want it to get above 68F for most ale strains.   With few exceptions (notably saison yeast) I'd want to keep it within 6F of my pitching temp, but that's me.
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Offline brushvalleybrewer

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Re: What does it mean to let a fermentation free rise?
« Reply #7 on: March 03, 2012, 06:48:11 AM »
Interesting responses, everybody. Thanks.
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Offline bluesman

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Re: What does it mean to let a fermentation free rise?
« Reply #8 on: March 03, 2012, 08:22:03 AM »
If I was letting a beer free rise, I would not want it to get above 68F for most ale strains.   With few exceptions (notably saison yeast) I'd want to keep it within 6F of my pitching temp, but that's me.

+1

There a few exceptions like Saisons, but for the overwhelming majority of ales, Tom is correct.

In the middle of the summer when my cellar reaches 68F. I like to pitch my American Ales around 62F and let them rise naturally, but I ferment in a chest freezer with a Johnson controller set at 68F.
Ron Price

Offline dcbc

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Re: What does it mean to let a fermentation free rise?
« Reply #9 on: March 03, 2012, 02:28:28 PM »
I asked this question and about temperature control jargon generally and got it answered on a July episode of Brew Strong.  If you're using a dual zone temp controller, you set your cold side to your ultimate set temp and leave your warm side, if any, below your pitching temp.  According to Jamil, if it doesn't rise to fermentation temp in about 24 hours, you might want to give it a little heating help.
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Offline brushvalleybrewer

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Re: What does it mean to let a fermentation free rise?
« Reply #10 on: March 04, 2012, 10:05:11 AM »
I asked this question and about temperature control jargon generally and got it answered on a July episode of Brew Strong.

Assuming you are “Doug in Texas,” I think I found it. It is the July 25th show. The funny thing is that episode does not show up in the iTunes subscription. I guess that explains why I had not heard it. It starts at 40:32.
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