Increase in gravity over a 60 minute boil

Discussion in 'Homebrewing' started by peter831, Sep 18, 2013.

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  1. peter831

    peter831 Initiate (0) Dec 2, 2012 California

    I have been using BeerSmith for some time now and trying to get it and my system in sync. I have brewed 15-20 batches, and they are getting really good, IMHO anyway.

    Occasionally it seems there is no way I can hit the final gravity when I start at the estimated preboil gravity.

    I know its about boil rate, evaporation rate.... volume in the preboil

    So, my question to you is, how much of an increase do you normally see from a pre boil gravity to the post boil - cooled wort OG?

    Does it differ with a high preboil gravity compared to a low preboil gravity?

    If I start with a preboil gravity of say 51, is it too much to think I will hit 67 with a starting vol of 8 gal and finishing with 5.25? Losing some in the boil kettle and in the 100' 3/8" copper line.
     
  2. mattbk

    mattbk Savant (1,111) Dec 12, 2011 New York

    ive made a dip stick i can place in the kettle that is calibrated to specific volumes in the kettle. i use it to get my initial pre boil volume and my final volume.

    based on these measurements, i know i boil at a rate of just about 1 gal / hr. this is probably a very common boiling rate.

    you can use the dilution tool in BS2 to estimate the effect of water on gravity. per instance, if im planning on making a 5 gallon 1.050 beer, at 6 gallons my gravity should be 1.042. dont forget to account for temperature effect on gravity when you take your measurements as well. you can use the hydrometer adjust tool for this!

    one final trick. i usually boil for 90 minutes - a little past my final OG - then add back some boiled water to nail my og exact. that little trick helps me account for slight varaitions in batch-to-batch efficiency/boil off rate.
     
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  3. TNGabe

    TNGabe Initiate (0) Feb 6, 2012 Tennessee

    Not sure what you mean by 'losing some', but if preboil is 51 GP and volume is 8 gallons, that's 408 total GP. If you boil it down to 5.25 gallons, 408/5.25 = 77.7 GP/gal. That's it, same for every beer no matter what.
     
  4. utahbeerdude

    utahbeerdude Maven (1,374) May 2, 2006 Utah

    I believe that the OP's 5.25 gallons is volume delivered to the fermenter, not post-boil volume in kettle (for which your calculation is entirely correct). To the OP: you need to accurately figure your losses (in transferring from kettle to fermenter) in order to be able to answer your question.
     
  5. inchrisin

    inchrisin Pooh-Bah (2,013) Sep 25, 2008 Indiana
    Pooh-Bah

    I try not to over complicate things. Once you get a volume into your kettle you DON'T lose any gravity points. From here on out you lose volume. You may lose a little potential gravity to your wort chiller, but I don't think you'll see that even measure out in brix or gravity on a hydrometer. More likely you'll lose a few drops off your batch volume and it's no sweat.

    To answer one of your questions, it's always about potential gravity (or sugar, as we'll call it) divided by volume.

    1 gal of 1.025 wort boiled down to 1/2 gal would be 1.050 wort
    1 gal of 1.050 wort boiled down to 1/2 gal would be 1.100 wort

    (This is @ 60F probably at sea level).

    If you halve the volume you will double the gravity.
     
  6. mikehartigan

    mikehartigan Maven (1,421) Apr 9, 2007 Illinois

    "When am I ever gonna use this stupid Algebra!?!?!?" - unknown
     
  7. sjverla

    sjverla Initiate (0) Dec 1, 2008 Massachusetts


    Well, to be fair, I've solved for X more since I started homebrewing than I did in the preceding 10 years after high school.
     
  8. peter831

    peter831 Initiate (0) Dec 2, 2012 California

    thanks everyone,

    Losing some meant I was losing wort in the lines... Due to very expensive water rates I added an immersion coil to my plate chiller, running the wort though the copper coil submerged in ice water allowing me to run the pump almost full blast and the water at a pretty slow flow, chilling my 5.25 gal in about 6-8 minutes.

    I get the GU's, and they are related to volume,

    I think my issue is I cant boil to 5.25 gal as mentioned above as I lose wort in my boil kettle (keg) and then in my lines.

    What I dont think I have ever done is measured the wort post boil but still hot, in the kettle. Maybe thats where I need to start.

    peter
     
  9. VikeMan

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

    You need to shoot for a higher post boil volume. Assuming your new chiller loss is the only issue, you'll need to add the chiller loss volume to your total (old) starting water (either the mash/sparge water if all grain, or the kettle starting water if extract).

    If All Grain... the extra water will cause a mash efficiency increase, but not enough to overcome the new (chiller) loss. So you'll need to adjust grain bills upward. Sorry...leaving sugar in the chiller means you need more sugar.

    If extract...the extra water will cause a lower OG, so you'll need to adjust your LME/DME amounts upward.
     
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