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04/17/08 03:12 PM  
predicting FG
Okay another question about this trippel that is stressing me out.


OG 1.08

Mash 60 min at 146 then 60 min at 153

1.75lb of sugar, the rest pale malt

This has been going now for almost two weeks and the gravity is still only down to 1.022 but the airlock is going about 9X per minute at close to 70 degrees.

Is there any way to know how low this will finish? Can I realistically hope to hit 1.012 so late in the game?

Seanywonton (Sean White)
04/17/08 03:41 PM  
Re: predicting FG
The only way you can know where it will finish is to wait, let it ferment out, and THEN take the f.g. If it doesn't finish out where you want, you can try restarting it with a fresh, krausening yeast starter.

I still highly recommend not mucking about in your beer to get a gravity reading. I only take a reading when I rack to secondary (sometimes) and bottle or keg (all the time).

04/17/08 03:51 PM  
Re: predicting FG
I second that. An impatient brewer is a disappointed brewer.
04/17/08 03:58 PM  
Re: predicting FG

But are there data out there that show rates of gravity drop given rates of bubbling or whatever?

04/17/08 04:23 PM  
Re: predicting FG
Not really--that kind of thing can be affected by changes in pressure, temperature, fill level of airlock, etc etc.


As for how the ferment is going, I believe there are some yeasts out there that may always take a couple weeks to finish out a beer (say, Dupont). That said, WY3787 is not one of them--my last tripel fermented out and dropped dead clear in less than 10 days. I am sure the reason for this is that I pitched at a very high rate (1.4 M/cells/ml/P).

If I recall, you pitched this tripel at a much lower rate, something like 1/10 of that. (I think we calculated that?) That doesn't mean your beer will necessarily be worse or better than mine. It does mean it'll take longer to finish. It should also increase your ester levels (which may be great, or may be excessive).

Anyway I think you have only two choices that make any sense. The first and probably best is to listen to Steve and Sean and just let it go for a while without messing with it. Regardless of whether it turns out great, okay, or bad, you'll learn a lot about 3787 and know more about how to work it.

The other choice is to rehydrate 10 grams of dry yeast and quickly pour it in (no readings, no samples, etc), which I would only suggest if you're more worried about making this one batch as good as possible than you are about learning how 3787 works for you. I'd do the former.


04/17/08 04:59 PM  
Re: predicting FG
You forgot one ingredient in your recipe - patience. My most recent triple remained in the primary for 4 weeks while I patiently waited for the final gravity.
04/17/08 05:17 PM  
Re: predicting FG
Thanks guys

I will wait. The next step I'm planning is to rebrew this beer (although with more hops and some oak) on the yeast cake. The massive increase in pitch rate will hopefully tell me something usefull.


04/17/08 06:41 PM  
Re: predicting FG
I don't know if anyone is interested in this (or if its even a valid analysis) but I just plotted the drop in gravity as a function of the number of days of fermentation (I've taken three readings as I'm trying to learn a bit about this yeast).

The decay in gravity is almost a perfect natural log of the nubmer of days of fermentation

That is, gravity is dropping as the function ln(days)

My model predict that I'll hit 1.012 on day 17

today is day 12

04/17/08 08:59 PM  
Re: predicting FG
Based on your ingredients and mash profile, I would expect you could hit 1.012.

How low did you pitch?

04/17/08 10:22 PM  
Re: predicting FG
how low like temp?

about 65

04/17/08 11:19 PM  
Re: predicting FG
"The decay in gravity is almost a perfect natural log of the nubmer of days of fermentation"

This is not in any form a rule or guideline of fermentation - it will do what it wants when it wants.

04/18/08 10:33 AM  
Re: predicting FG
"The massive increase in pitch rate will hopefully tell me something usefull."

I'm not so sure, unless you somehow prepare that cake so that the cells are in the same physical shape as the cells were on this go-round. Otherwise it's just not apples to apples and it's hard to compare what's going on.

One way to make it more apples-to-apples is to take however much slurry you want to repitch for your next batch, and put it on your stir plate with a pint of starter wort for a few hours. This will get it into a state that's more similar to the extremely healthy propagated cells you pitched on this batch.

By the way, unless you have some innovative sampling method, the more samples you take from your batch, the more oxygen you let in there. There are few absolutes, but I doubt many people would disagree that repeatedly letting air into a batch that's past high krausen is a "bad thing."

04/18/08 11:34 AM  
Re: predicting FG
Oh I'm anything but innovative.

I will be making a newly stirred starter though.


04/26/08 07:10 PM  
Re: predicting FG
FG 1.008!

04/27/08 02:42 PM  
Re: predicting FG
Wow, that's a pretty low FG! - looks like 90% apparent attenuation, and Wyeast lists 72-78% as typical for this strain.

How did the rest of the fermentation progress compare to your anticipated logarithmic curve?

04/27/08 02:50 PM  
Re: predicting FG
Well to give you some idea, the r-squared was 0.9987

for the log plot.

I'd say it was highly predictive.


04/28/08 10:26 AM  
Re: predicting FG

Interesting. Is this the beer you pitched with the 300mL of slurry from the starter we talked about?

BTW, what FG would be predicted by your log "model"?

04/28/08 11:10 AM  
Re: predicting FG

this is the very one indeed.

The plot has pretty much hit its asymptote so 1.008 maybe 1.007 is about the predicted FG as well as the actual FG.

04/28/08 11:17 AM  
Re: predicting FG
check it:


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