Gravity Question

Discussion in 'General Brewing Discussions' started by Nola_Brew, Jul 25, 2016.

  1. Nola_Brew

    Nola_Brew Active Member

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    I brewed a 3.5 gallon SNPA clone Sunday. I usually use the Priceless calculator to determine strike water volume. For this recipe it called for 5.35 gallons. Boil off is set at 1 gal/hr. I had about 1/4 gallon left which is what the calculator said I should have and is normal for my brews.

    My preboil OG was 1.042 which is about normal for me. The problem was the post boil gravity which ended up at 1.062 (supposed to be 1.053).

    Not sure what caused the increase. I boiled for 60 min/ mashed for 60 min.

    When I checked the strike water volume on BF it shows 5.04 gallons.

    If anything my OG should have been lower, not higher.

    By the time I chilled my wort, and the sample was chilled enough to check it was too late for me to add any additional water. Total grain bill was right under 7 lbs.

    Any ideas what could have caused the increase? Also what can I expect from the finished product?
    I used 1056 slurry that took 8 hrs to take off and is currently chugging away.
     
  2. Ozarks Mountain Brew

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    you just had a boost in efficiency, try to recall your exact steps in detail and change the efficiency next brew and see if it matches
     
  3. Nosybear

    Nosybear Well-Known Member

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    Here's how to think about it: In the mash, you produce sugars. Once the wort hits the kettle, the amount of sugar you have is constant, only changed by inefficiencies, i.e., leaving wort behind as in dead space or hop absorption. "Gravity points" is a way of thinking about this. In the boil, the equation looks like this: G1/G2=V1/V2 (and you thought you'd never use those proportions from high school algebra!). Working backward it looks like this: 3.5 gallons * 62 gravity points divided by 42 gravity points gives me 5.17 gallons of initial wort before you started the boil. What this tells me is you don't have any magical increase in sugars! Assuming no losses to dead space, the 7 gallons of grain should absorb about 1.5 gallons of water, so we're at about 7 gallons total water used.

    7 pounds of base malt will yield 217 gravity points (7 pounds * 31 point-pounds/gallon). Divide that by your volume, initial or final, and you'll get what the gravity should be. Divide 217 by 3.5 and you get 62, or 1.062 OG. Looks to me like the calculator was dead on! Using the initial volume you mention, I get 1.041 for the gravity, which matches what you cite. Again, dead on. There's no increase - you somehow didn't use enough water!
     
  4. jeffpn

    jeffpn Well-Known Member

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    That's exactly what I can't wrap my head around, nosy. That's why I'm concerned about ending kettle volume. Hit my water level (and gravity) preboil. Then I check my water level and gravity in the kettle post boil. Yes, I'm throwing product away, but I know how much I want to have in the fermenter. 6.5 gallons in the boil kettle after my boil does the trick.
     
  5. Nola_Brew

    Nola_Brew Active Member

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    From a water standpoint, I used what Priceless said. I also use the calculator on the BIAB site and it was the same. The only thing I can think of to cause the calculator to give a lower strike water volume would be the loss inputs.
    Inputing using the Priceless calculator, I do not enter any info in the mash thickness or sparge volume since am a BIAB brewer.

    Grain absorption is .08/ hop absorption is .040/ boil off 1 gal/hr/ kettle loss, packaging loss, mash tun loss all at .35. These inputs show a total water volume at 5.88 gal, which is a little higher than what I used. Still doesn't come anywhere near the 7 gallons as shown in the above post.

    When I brew 2.5 gallon batches I normally use approx. 5 gallons water. Increasing my batch to 3.5 I probably should have used at a min of 6 gallons which ultimately I was a .5 gal short.
     
  6. Nosybear

    Nosybear Well-Known Member

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    Rule of thumb that works well for my thumb: For six gallons in the kettle at the end of the boil, I start with 10 gallons of brewing liquor. I have set up my profile in this app, it generally recommends somewhere between 9.5 and 10.5 gallons, depending on the grain bill. Losses to account for are grain absorption, dead space in your lauter tun, hop absorption, boil-off, dead space in your kettle, hoses, pumps, etc. You generally lose 0.2 gallons per pound of grain, 1.4 gallons for 7 pounds of grain, I don't see that in the calculation. So we have 3.5 gallons of wort to the kettle, 1.4 gallons for absorption, a gallon for boil-off, hop absorption is negligible, 0.35 gallons lost to dead space. So yes, I get about 5.5 gallons of liquor required to produce the amount of wort you want. Squares with my rule of thumb proportions. You need 185.5 points to produce 3.5 gallons of 1.053 wort (3.5 gallons * 53 points). That's six pounds of grain within measurement error (185.5 points/31 points/pound). So we found your problem: You used one pound too much grain to produce the wort you wanted. The question is how did you arrive at the amount of grain to use. Was there a no-sparge option you might have accidentally checked? Maybe BIAB instead of all-grain using a Mash-Lauter Tun? I don't know how but somehow your recipe builder told you to use a pound of grain more than you needed.

    It's advantageous to learn to do the calculations by hand even if you never really do (kind of like high-school algebra). That way when something like this comes up you can check yourself or even notice when a result looks wrong. John Palmer's "How to Brew" is just about the best homebrew reference for the calculations I can think of. Once you can build a recipe by hand, the calculators make more sense.
     
  7. artbreu

    artbreu Member

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    Boil losses have been very hard (impractical) for me to nail down. First, if you're using gas, how can you ensure the same flow from brew to brew? With a heating element that has a thermostat, maybe more practical, but ambient conditions will still effect your losses.

    At some point, unless you're going the extra mile to control all of these variables (fun to some, pointless to others), you'll learn how to work your numbers in your specific case and you'll tweak to "perfection" from there.
     
  8. Nosybear

    Nosybear Well-Known Member

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    I can only approximate mine: My propane-fired burner sits on the back porch and it does get windy in Colorado from time to time. I have inconsistent boils to deal with. But all told, using the proportions mentioned above, it's possible to correct, just plan on boiling off more than you think and add water at the end. That said, I usually hit within 0.002 of my intended gravity so I seldom have to add anything.

    There are, however, exceptions where having some DME on hand has been handy.
     
  9. Nola_Brew

    Nola_Brew Active Member

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    I use Brewers Friend for all my recipe calculations. The main recipe for this batch came from HBT and I scaled it down using BF to 3.5 gal. The OG shows 1.053 using just under 7 lbs of grain and that's with 6 gallons of water vs 5.5 that I used. I find it hard to believe that a half gallon would have increased the OG as much as it did.
    I've brewed 30 batches so far and only had one other time that my OG was elevated. Coincidently that brew was also 3.5 gallons but was a 1.063 OG and used almost 8 lbs of grain.

    I guess I do need to learn manual calculations but since the BF site does it for me I just never found a need to manually do it. I do have Palmers book and read it when I first started brewing, which was over a year ago. Maybe I'll have to re-visit it for a re-fresher course.

    What I do not get is the other brews I did in 3.5 gallon version were all over 1.060 and used 8+ lbs of grain. This brew was supposed to be 1.053 and used a pound less of grain.

    Next batch I brew will be the 2nd version of a NE IPA I did and I will use 6 gallons of water. that particular grain bill stands at 7.24 lbs (OG of 1.055) and that's using 6 gallons of water.
     

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