Fast Ferment Test Lower FG than Batch

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ryanjbrowne

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HBT:

I have two batches for which I've done fast ferment tests. The FG on both fast ferment tests are 6 points lower than the batches themselves, which are not budging after extend stay in their fermenters. Same yeast pitched into FFT as into the batch (Wyeast 1728 with BIG starter for SG 1.091, and big starter of Wyeast 2565 for SG 1.070 for the other), set the FFT in warm area, shook it to resuspend yeast, took gravity readings on FFT at 3 and 7 days. Batches have been in primary for 4+ weeks.

Perhaps poor aeration of the batches?

Have others had the FFT finish lower due to the sheer amount of yeast pitched at it? I know the FFT sheds light on the limit of attenuation of that wort, so my FFT shows there are still fermentables in there.

Major point: I want to bottle condition these two batches for sometime and need to know if I should take the final 6 points into consideration when priming so as to prevent any sort of overcarbed / bottle bomb scenario...or would the yeast be so stressed/tired at this point that those final 6 points won't be gobbled up?
 
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ryanjbrowne

ryanjbrowne

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UPDATE:
After adding the benzomatic O2 canister and oxygen system (left-hand regulator, tubing, and carb stone) and running O2 for 30-45 seconds before pitching, I've had every batch attenuate either dead-on with the FFT or only 1 point off. This seems to be pretty convincing -- tho admittedly anecdotal -- evidence that oxygenation was my previous issue with batches not attenuating down to where the FFT indicated was the limit of attenuation.

Hope this helps anyone else using FFTs!
 

erikpete18

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Thanks for checking back in! Just out of curiosity, how were you aerating before you got the O2 setup? I'm not surprised that O2 is better than even heavy aeration, but 6 points is a fair bit of difference and might push me towards picking up an O2 set. If nothing else, it looks like taking a FFT might be a good method to use to test aeration of a batch; if the FFT ends up at about the same FG consistently the aeration technique must be working, but if the FFT is consistently lower, then maybe the aeration needs to be improved.

Also, just as an aside, have you started changing up your recipes to account for the better attenuation? If your beers were still tasting good before the O2, I could see myself adapting recipes to account for the extra FG points, then having to readjust once I got an O2 setup going. Maybe mash a little higher, or throw in a little more crystal. I recently changed aeration techniques (shaking carboy -> aquarium pump/aeration stone) and seem to be finishing lower than I've been expecting. I'd been attributing it to other changes I've made at the same time, but now I'm wondering if I'm just getting better aeration and need to adjust my recipes. Maybe I've got a FFT in store next batch!
 
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ryanjbrowne

ryanjbrowne

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As a preface, certainly there are a number of variables that can affect attenuation aside from aeration/oxygenation (pitch rate, yeast health/viability, mash conditions, pH, calcium, zinc, etc., etc.). It's after controlling for as many of those variables as possible, I can fairly confidently say it is the switch to O2 via a carb stone that has had such a dramatic affect on my final attenuation. The fun of homebrew is all the variables, knobs, levers we can tinker with...but that is also where it can be work intensive to find which of those are causal in the effect we're looking for.

Anyway, before the O2, I was just rocking the carboy. Mainly, my reasoning here was after watching a lecture from a rep from Wyeast say that in their lab tests, rocking for about 1.5 minutes dissolved as much O2 into solution as rocking for 5 minutes (which is what I used to do). Not sure how much O2 is dissolved via aeration, but I suspect it is similar to rocking, perhaps a bit better. But, as you probably know, rocking and aeration are only drawing in the O2 in the air, which composes only about 20% of air. O2 is pretty much 100% O2.

Your thoughts on recipe composition is a great one, too. Since moving to O2, I have seen a corresponding effect as a result of mash mechanics--mash temp, pH, malt bill (crystal, base, etc.). For instance, I'm a huge fan of pales and IPAs with zero crystal. Previously with rocking, I'd have a recipe with 80% 2 Row, 15% Vienna, 5% carapils/wheat, mash at 150/152, pitch Wy 1968, and it'd attenuate to 1.015 or so (with a FFT of 1.010). It was fine, but a bit sweet with still fermentables left in solution. After O2, same grain bill, mash profile, yeast, and I'd get an attenuation of 1.011/1.010. Nice dry finish that lets the hops pop. Small example, but an illustrative one, I think.

Keep me updated on where ya go!
 

Alexholsch

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i just read that if you over agitate the fft it can lead to greater attenuation than what you will get from your normal fermentation. read this in the methods of the **************** which is a LODO web page.
 
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