Author Topic: stuck fermentation ;(  (Read 787 times)

Offline octess

  • Cellarman
  • **
  • Posts: 41
  • the octess project
    • View Profile
stuck fermentation ;(
« on: March 27, 2011, 08:41:10 PM »
Hi all!
I recently brewed a cocoa stout. problem is attenuation is too low : 55%
any insights? here are the specs:
OG: 1.062
FG: 1.028
1st fermentation : 2 weeks at 70F, 2nd : 1 week at 70F. attenuation didn't change from racking.
yeast used : WLP036 dusseldorf (altbier) close to the expiring date, though well kept in fridge.
2 litres starter 18 hours prior to pitching for a 40L batch, which perhaps wasn't vigorous enough - though the actual fermentation seemed to be quick and sufficiently vigorous.
oxygenation of the wort was just as usual.
mash procedures: too hot at first (80 celcius) and brought back to 67 celcius with the addition of cold water after 15 minutes. perhaps denatured too many enzymes (to break down long chain sugars), thus not enough fermentables and too many unfermentables in the wort? though the conversion with the iodine test was OK after 90 minutes of mashing...
HELP!
Thanks ahead!
Viva el art of brewing alchemy!

Offline jeffy

  • Brewmaster General
  • *******
  • Posts: 2449
  • Tampa, Fl
    • View Profile
Re: stuck fermentation ;(
« Reply #1 on: March 28, 2011, 04:06:27 AM »
Hi all!
I recently brewed a cocoa stout. problem is attenuation is too low : 55%
any insights? here are the specs:
OG: 1.062
FG: 1.028
1st fermentation : 2 weeks at 70F, 2nd : 1 week at 70F. attenuation didn't change from racking.
yeast used : WLP036 dusseldorf (altbier) close to the expiring date, though well kept in fridge.
2 litres starter 18 hours prior to pitching for a 40L batch, which perhaps wasn't vigorous enough - though the actual fermentation seemed to be quick and sufficiently vigorous.
oxygenation of the wort was just as usual.
mash procedures: too hot at first (80 celcius) and brought back to 67 celcius with the addition of cold water after 15 minutes. perhaps denatured too many enzymes (to break down long chain sugars), thus not enough fermentables and too many unfermentables in the wort? though the conversion with the iodine test was OK after 90 minutes of mashing...
HELP!
Thanks ahead!

I'd say that 80C (167F) denatured all of the Beta enzymes and a lot of the Alphas, which would give you a lot of unfermentable wort and a high finishing gravity.

70F is pretty warm for fermenting, btw.
Did you measure the gravities with a hydrometer or a refractometer?  I ask because alcohol will not allow an accurate reading with a refractometer after fermentation has begun.
Jeff Gladish, Tampa (989.3, 175.1 Apparent Rennarian)
Homebrewing since 1990
AHA member since 1991, now a lifetime member
BJCP judge since 1995

Offline denny

  • Administrator
  • I must live here
  • *****
  • Posts: 11706
  • Noti OR [1991.4, 287.6deg] AR
    • View Profile
    • Dennybrew
Re: stuck fermentation ;(
« Reply #2 on: March 28, 2011, 08:48:13 AM »
though the conversion with the iodine test was OK after 90 minutes of mashing...

That really tells you virtually nothing.
Life begins at 60.....1.060, that is!

www.dennybrew.com

The best, sharpest, funniest, weirdest and most knowledgable minds in home brewing contribute on the AHA forum. - Alewyfe

Offline bluesman

  • Global Moderator
  • I must live here
  • *****
  • Posts: 8689
  • Delaware
    • View Profile
Re: stuck fermentation ;(
« Reply #3 on: March 28, 2011, 09:03:53 AM »
I'd say that 80C (167F) denatured all of the Beta enzymes and a lot of the Alphas, which would give you a lot of unfermentable wort and a high finishing gravity.

70F is pretty warm for fermenting, btw.
Did you measure the gravities with a hydrometer or a refractometer?  I ask because alcohol will not allow an accurate reading with a refractometer after fermentation has begun.

+1

Mashing at 80C could be a problem especially for 15 min.
Ron Price

Offline Kirk

  • Assistant Brewer
  • ***
  • Posts: 175
  • Sparks, NV
    • View Profile
Re: stuck fermentation ;(
« Reply #4 on: March 28, 2011, 01:03:50 PM »
+2  Hey, I'm into "cheap and easy" posts today. 8)
Kirk Howell

Offline octess

  • Cellarman
  • **
  • Posts: 41
  • the octess project
    • View Profile
Re: stuck fermentation ;(
« Reply #5 on: March 28, 2011, 02:03:36 PM »
Did you measure the gravities with a hydrometer or a refractometer?  I ask because alcohol will not allow an accurate reading with a refractometer after fermentation has begun.

hydrometer. that's what I thought too about the enzymes but since the fermentation started well, I guessed it was OK.
Viva el art of brewing alchemy!

Offline octess

  • Cellarman
  • **
  • Posts: 41
  • the octess project
    • View Profile
Re: stuck fermentation ;(
« Reply #6 on: March 28, 2011, 02:08:15 PM »
That really tells you virtually nothing.

mind me asking...why?
or should I say: what is the purpose of that test then?
thanks!
Viva el art of brewing alchemy!

Offline octess

  • Cellarman
  • **
  • Posts: 41
  • the octess project
    • View Profile
Re: stuck fermentation ;(
« Reply #7 on: March 28, 2011, 02:14:21 PM »
another: do you think that the wort is going to be especially hazardous to bacterial contamination - or other buggers?
and also, any idea about what to do with the wort before bottling?
it does taste pretty good! and surprisingly not overly sweet!
thanks
Viva el art of brewing alchemy!

Offline jeffy

  • Brewmaster General
  • *******
  • Posts: 2449
  • Tampa, Fl
    • View Profile
Re: stuck fermentation ;(
« Reply #8 on: March 28, 2011, 02:18:04 PM »
No worries.  If you like the taste, drink it up.
The last beer I did that to (high initial mash temp) I gave up on the yeast and added brett to it.  It's getting nicer all the time.  (See my photo on the "show us your pellicle" thread.)
Jeff Gladish, Tampa (989.3, 175.1 Apparent Rennarian)
Homebrewing since 1990
AHA member since 1991, now a lifetime member
BJCP judge since 1995

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3174
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: stuck fermentation ;(
« Reply #9 on: March 28, 2011, 03:27:32 PM »
or should I say: what is the purpose of that test then?

A negative iodine test (if it's done correctly, which is a big "if") tells you that there are no starches left in the wort. It doesn't tell you anything about what kind of sugars you've created. I think that's what Denny was getting at, anyway.
Beer is like porn. You can buy it, but it's more fun to make your own.
http://seanterrill.com/category/brewing/