Original Gravity, Final Gravity, and Efficiency

Discussion in 'Beginners Brewing Forum' started by TetersMillBrewing, May 18, 2020.

  1. TetersMillBrewing

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    My first of probably many dumb questions over the next few weeks and months.

    Each of the three recipes I have brewed have an original gravity and final gravity listed. Do I assume correctly that the original gravity listed is based simply on the grain bill and efficiency I have in the system?

    How much does final gravity have to do with volume in the fermentor vs my original gravity. I ask about the final gravity because I did not fully understand my equipment losses and ended up with less in my fermentor than expected. I am just trying to sort out some of the numbers since I am obviously in overload when I Iook at the brew log information.

    My first three brews / Software original gravity / my measured original gravity after boil
    Strawberry Blonde Ale / 1.059 / 1.057
    Oatmeal stout / 1.074 / 1.072
    The third was a recipe found on this site. The snapshot recipe has an efficiency of 70% which is lower than the efficiency I have and I don't know how to change it for my snapshot.
    Chocolate Coffee Stout / 1.065 / 1.070

    Thanks
     
  2. Nosybear

    Nosybear Well-Known Member

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    Original gravity is based on the amount of extract from the grains (the grain bill), your efficiency at extracting that extract (your efficiency) and the volume of water the extract (the sugars, dextrines, proteins, etc. that make it into your wort) is dissolved in. Final gravity has nothing to do with the volume in the fermentor - the same wort with the same yeast under the same fermentation conditions will ferment out to the same final gravity regardless of the volume. Hint: If you brew a five-gallon recipe, you will likely end up with less than five gallons in the fermentor unless you dump everything in, and then some of the volume will be trub and hop debris so it is inevitable that you will have less than 5 gallons in the fermentor. You'll package even less than that due to the volume of yeast left behind. I brew at 5.5 gallons to make up for these losses.
     
  3. TetersMillBrewing

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    Thanks Nosybear, that just confirms what I had expected looking at the numbers.I leaned very quickly on my first batch that there is a significant difference between final kettle volume vs initial fermentor volume and have started adjusting my grain bills accordingly.
     
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  4. Blackmuse

    Blackmuse Well-Known Member

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    Sounds like you are catching on quick and hitting some numbers nearly spot on!

    For the 3rd beer have you tried editing the recipe and adjusting the efficiency to match yours? BTW - watch IBUs when you adjust efficiency because they will change too - unless you "scale" the recipe based on efficiency. "Scale" can be found in the recipe tools tab while you are in edit mode.
     
  5. TetersMillBrewing

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    #5 TetersMillBrewing, May 18, 2020
    Last edited: May 18, 2020
    I never looked at the recipe tools while I was in edit mode, nice to know. I simply ran the grain bill knowing it would come out with a higher original gravity. Now that I have taken the time to look I see where I can change efficiency my numbers should have been much higher on the third batch. I think the root cause of the poor original gravity (should have been 1.079) was a "not as vigorous" boil. My buddy was in town and I let him manage the bulk of the process. After it was done we concluded that the boil should have been harder as we didn't lose the amount of wort as I had figured.

    I actually have a fair amount of experience with all-grain and calculating expected gravity, normally with just corn, wheat, barley, and rye, just never boiled and added hops :). .
     
  6. Blackmuse

    Blackmuse Well-Known Member

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    Nice! That explains why you have been hitting some solid numbers.
     

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