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.
     
  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.
     
  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.
     
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  4. CurtFromHershey

    CurtFromHershey Initiate (0) Oct 4, 2012 Minnesota

    What temperatures were your samples?
     
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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.
     
  6. koopa

    koopa Initiate (0) Apr 20, 2008 New Jersey

    Nothing could.
     
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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.
     
  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
     
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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).
     
  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!
     
  11. machalel

    machalel Initiate (0) Jan 19, 2012 Australia

    Good point, forgot about that one!
     
  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
     
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