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Old 11-10-2010, 03:10 AM   #1
kidsmoke
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Default FG too high...in the fast/forced fermentation sample.

So I decided to brew up a dry stout and attempt to do a fast/forced fermentation (FFT) on ~8oz (enough to take a hydrometer reading). That was Friday. Fast forward to yesterday and today — the FFT has finished fermenting while the main fermentation is continuing to bubble away. I check the FG on FFT sample...and it's 1.020 or a 57% apparent attenuation! (OG was 1.048) That's more than 8 points from what I expected (1.012). For those of you who have conducted FFT, how accurate is the final gravity to the real thing?

Just for reference my mash schedule was 152/153 for 90 minutes with a 10 minute mashout around 165. (Higher mash temp to compensate for US-05's higher attenuation.) The grain build was based around the BYO's dry irish stout recipe with pale chocolate malt substituted for the chocolate malt and a half-ounce of Dehusked Carafa II for color.

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Old 11-11-2010, 02:35 PM   #2
COLObrewer
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I don't see how the silly FFT thing could work at all, there are too many variables that would be different between the main batch and the satellite batch, here are some threads discussing it.

http://www.homebrewtalk.com/f39/beer-178740/

http://www.homebrewtalk.com/f39/sate...chnique-68522/

http://www.homebrewtalk.com/f39/sate...ermenter-5014/

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Old 11-11-2010, 04:35 PM   #3
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I think the difference between those threads and what I've done was pitch a separate amount of the same yeast used (at a greater rate) just for the FFT sample rather than drawing off from the pitched carboy wort. I also fermented it at a higher temperature so the yeast would work it's way through the wort sample quickly.

I think these steps* mitigate any separate factors concerning the amount or performance of the yeast compared to the actual fermenting beer. I mean really I'm just trying to get to the limits of the wort's fermentability. The actual beer may or may not reach this limit, and could be higher since the pitch rate of the actual beer is lower.**

Truthfully, after thinking about the original topic a little more, I wonder if mashing at 152 for so long and mashing out at 165, rather than at 170, may have released more dextrins than I hoped due to the alpha amalyese being "on" for so long. (Assuming that this FFT is correct.) My efficiency was about 8% higher than I expected, so that's not really outside the realm of possibilities.


*And as a result made a really awful sour tasting sample as I learned today.
**All of this lovingly paraphrased from Kai's FFT page.

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Old 01-25-2011, 04:31 AM   #4
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Just a minor update, the FFT sample ended up finishing around 1.017 while the final batch was around 1.018. It's been a month since I bottled and I haven't gotten any overcarbonation. I've since used FFT for other beers with success as well..

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