gravity increase after boil - same volume

Discussion in 'Homebrewing' started by sveltman, May 17, 2015.

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  1. sveltman

    sveltman Initiate (0) May 17, 2015

    Just wondering if anyone can help explain something - I just finished a batch of beer, doing a mini BIAB brew. The preboil gravity of my 3 gal wort was 1.031, which was close to expected. However, after adding hops, boiling for 60 min, cooling and adding water to top up to 3 gallons again, the OG was 1.040. BeerSmith calculated a preboil gravity, and OG of 1.032, which makes sense.

    Can anyone explain what may have caused an increase in gravity to the same volume of wort?

    Thanks.
     
    #1 sveltman, May 17, 2015
  2. TomTown

    TomTown Initiate (0) Feb 7, 2011 Texas

    How certain are you of the volumes? Primarily the pre-boil, as you likely have double/triple checked the post volume now.

    If the gravity had dropped after the top-up, one would just assume that you lost some of the "good stuff" to trub during a transfer, but you're right; an increase is a little more confusing.
     
    #2 TomTown, May 17, 2015
  3. VikeMan

    VikeMan Grand Pooh-Bah (3,067) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    What were your pre-boil and post-boil (after topping off) volumes exactly?

    ETA: You probably didn't mix the top-off water and the wort completely before taking your second sample.
     
    #3 VikeMan, May 17, 2015
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  4. CurtFromHershey

    CurtFromHershey Initiate (0) Oct 4, 2012 Minnesota

    What temperatures were your samples?
     
    #4 CurtFromHershey, May 18, 2015
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  5. sveltman

    sveltman Initiate (0) May 17, 2015

    Thanks for your replies. I am 100% certain on the volumes. I thought that VikeMan made a good point but I rechecked the gravity on the wort (I have aerated and mixed very well since the first time I measured) and I got 40 again.

    I did not measure the temperature on the preboil but I think it may have been around 130 -140 F. The temp on the OG measure was about 70.
     
    #5 sveltman, May 18, 2015
  6. koopa

    koopa Initiate (0) Apr 20, 2008 New Jersey

    Nothing could.
     
    #6 koopa, May 18, 2015
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  7. machalel

    machalel Initiate (0) Jan 19, 2012 Australia

    There's pretty much only 3 things that could have happened:

    1) Incorrectly measured volume (pre- or post-boil)
    2) Incorrectly measured SG (pre- or post-boil)
    3) Incorrectly mixed wort (post-boil)

    The only way the gravity would have increased otherwise is if you added more sugars.
     
    #7 machalel, May 18, 2015
  8. Hanglow

    Hanglow Pooh-Bah (2,051) Feb 18, 2012 Scotland
    Pooh-Bah

    Assuming you used a hydrometer, it's the temperature that throws it right off

    there are calibration calculators but I don't think they are particularly accurate if its too hot
     
    #8 Hanglow, May 18, 2015
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  9. warchez

    warchez Zealot (545) Oct 19, 2004 Massachusetts

    Temperature does seem the culprit.
    A 140F wort reading of 1.031 should read 1.044ish at 68F (calibration temp).
     
    #9 warchez, May 18, 2015
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  10. sveltman

    sveltman Initiate (0) May 17, 2015

    I was not aware that hydrometer readings needed to be adjusted for temperature. The readings I reported were unadjusted, so that definitely is the explanation for the difference. Thanks everyone for your replies!
     
    #10 sveltman, May 18, 2015
  11. machalel

    machalel Initiate (0) Jan 19, 2012 Australia

    Good point, forgot about that one!
     
    #11 machalel, May 19, 2015
  12. PapaGoose03

    PapaGoose03 Grand High Pooh-Bah (6,057) May 30, 2005 Michigan
    BA4LYFE Society Pooh-Bah

    Here's a link to Palmer's How to Brew online conversion table.
    http://www.howtobrew.com/appendices/appendixA.html
     
    #12 PapaGoose03, May 19, 2015
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