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Thread: attenuation issue

  1. #1
    Join Date
    Mar 2006
    Posts
    186

    attenuation issue

    Before I go ahead and email White Labs, I thought I would do some collective trouble shooting here (since yeast may not be to blame).
    I'll get right to it.....Here are the stats:

    Brewed a stout using (5th generation) Bristish strain I use, quite often with superb results.

    O.G 15.1 Plato

    75% British Pale malt
    13% Dark malts (Chocolate, Roasted and Patent)
    6% 60L Crystal
    6% Carapils

    Infusion Temp: 154 (1) hour

    Fermented at 65F

    YES I oxygenated correctly, YES I knocked out at 70F

    Gravity dropped to 6.5 in 8 days. Not to shabby. Fermetation has slowed down to almost a dead stop 6 days later, gravity only 5.4

    I wanted this to be a dry imperial style stout. Ironically, with all that sugar still in it, it's not at all sweet! It tastes like a well attenuated dry beer! That's when I began to suspect my hydrometer being off. I checked another beer, and it seemed spot on.

    I thought maybe (since I never brewed a stout to this caliber) it was my formulation. With only 6% crystal, I don't see how, especially at 154 degrees . The dark malts shouldn't leave behind that much residual sugar either.

    Then I thought, maybe I under-pitched, or harvested too early.

    I also thought, maybe I shut a previous beer in too early, and put the yeast under too much pressure (that did actually happen...Ooops )

    Either way, I ordered more yeast. My question is:
    (1) What do you suspect happend here
    (2) Why does the beer seem so dry, when the hydrometer says different.

    Thanks,
    Jay

  2. #2
    Join Date
    Oct 2002
    Location
    Athens, NY
    Posts
    432
    I ran into a similar problem several years ago. It turned out that my mash tun thermometer was off (by 6 degrees!). Have you checked all of your temperature probes to make sure that you actually mashed and fermented at the temperature you intended to?

    just a thought...
    Hutch Kugeman
    Head Beer Guy
    Crossroads Brewing
    Athens, NY

  3. #3
    Join Date
    Jul 2005
    Location
    Chandler, AZ
    Posts
    209
    Darker beers tend to mask sweetness, so your stout may seem dry despite having plenty of residual sugars. It's especially evident when you taste the wort. The first few times I brewed a darker beer, I tasted the wort before checking the gravity and thought it would be somewhere around 12 Plato but it ended up being over 16 Plato. I had to train myself to not freak out when I didn't taste a super sweet wort when I brewed that beer.

  4. #4
    Join Date
    Apr 2006
    Location
    Chicago, IL
    Posts
    185
    I double Kugeman. Check your thermometers!

    Also, always, a good practice is to pre-determine your final attenuation with a small amount of wort (say, 1/2 pint) and a huge dose of yeast on the side. it will give you a good idea if the fermentation is going right.

  5. #5
    Join Date
    Mar 2006
    Posts
    186
    How does one test a thermometer's accuracy on a MV? (sorry if it sounds like a stupid qu.. It just never occured to me this could be a problem, so I never thought about it).

  6. #6
    Join Date
    Oct 2002
    Location
    Athens, NY
    Posts
    432
    I suppose it depends on how your mash tun is designed, but on mine I just removed the thermal probe tri-clamp, and then unsrewed the housing around the actual thermometer. Then just drop it in a bucket of ice water and presto! I usually put another thermometer that I know is accurate in the ice water to make sure that I'm getting a true reading. Once I determined it's accuracy (or innaccuracy) in ice, I usually pull some water from the hot liquor tank to test the accuracy in mash ranges (155 F) just to double check.
    Hutch Kugeman
    Head Beer Guy
    Crossroads Brewing
    Athens, NY

  7. #7
    Join Date
    May 2004
    Location
    St. John's, Newfoundland, Canada
    Posts
    819
    testing thermometers

    bucket of ice with a little water = 0C

    boiling kettle = 100C

    Pax.

    Liam

  8. #8
    Join Date
    Jun 2005
    Location
    Lexington, KY, USA
    Posts
    78

    Testing thermometers.

    It is a bit more involved than that - testing of thermometers. In Denver water does not boil at 100 C because of the pressure. Same reason baking has to be done a little differently there.

    Look at the ERTCO (Everready Thermometer Co) for advice on temperature and correction.

  9. #9
    Join Date
    Dec 2003
    Location
    Strongsville, Ohio
    Posts
    244
    Yea...you definately want to test it in the range that is used. Thermometers do drift a degree or two or three between 32f and whatever your boiling point is.

    Ive looked a few times for a precision lab grade calibration thermometer but I never got one...cant remember if I couldnt find one or was just freightened by the price.

  10. #10
    Join Date
    Mar 2006
    Posts
    186
    Thank you, everyone. Cleaning the entire brewhouse tomorrow, will check it then.

    Thanks!
    Jay

  11. #11
    Join Date
    Nov 2006
    Location
    Escondido, CA USA
    Posts
    7
    I second the idea of doing a forced fermentation on the wort to test what your final gravity should be. It's a very valuable test that in 24 hrs can tell you whether you've got a mash temperature problem or a yeast problem.

    I also recommend checking cell counts during the fermentation, if the yeast cells aren't remaining in suspension, the fermentation will hang.
    A viability check on youir yeast will also help determine the cause.

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