Pre-boil efficiency: I hit my numbers, but eff. is off

Discussion in 'Brew Sessions' started by cassa, Feb 21, 2017.

  1. cassa

    cassa New Member

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    I have a brew session where the numbers don't make sense to me.

    Here's what I think is the relevant info from the recipe (it's BIAB if that matters):
    1. Efficiency: 70% (ending kettle)
    2. "Starting boil volume" under Water Requirements: 2.88 gal (it's for a 2.5 gal batch)
    3. "Recipe based estimate" of boil gravity: 1.048
    I thought that boil gravity would be same as "pre-boil gravity" in the Brew Log, so I expected that if I collected 2.88 gal from the mash, and if my pre-boil gravity was 1.048 or better, then my pre-boil efficiency in the log would be at least 70%. So, I was surprised when I recorded the following in the log:
    1. Pre-boil volume: 2.9 gal (i.e. essentially identical to what was expected)
    2. Pre-boil gravity: 1.051 (i.e. more concentrated than expected)
    3. Calculated pre-boil efficiency: 67% (i.e. less than recipe efficiency)
    I know that pre-boil efficiency is not "the same" as ending kettle efficiency, but the FAQ says Ending Kettle Efficiency is:
    Theoretically the same as Pre-Boil Efficiency, provided accurate measurements at both points (minus rounding error)

    What am I missing or misunderstanding? Thanks in advance for any help understanding this.
     
  2. Ozarks Mountain Brew

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    just some clarification, in your recipe do you have the brew method set to bib and you have your equipment profile correct or are you using defaults and if so did you select that profile in the recipe?
     
  3. cassa

    cassa New Member

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    Yes, it's set to BIAB, and using my BIAB equipment profile.
     
  4. Trialben

    Trialben Well-Known Member

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    That's a small brew if I had the same gravity at your us 5 gallons it would be well into 80s I'm sure.

    What's the gravity going into fermentor and your brew house efficiency?
    That's what you want dialled in everything in between isnt worth much.

    Here's a pic of my latest brew.
     

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  5. cassa

    cassa New Member

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    My gravity going into the fermentor was fine, but the volume ended up being low (and thus brewhouse efficiency was low). But I don't see how that would help explain why my pre-boil volume and gravity targets were met without my efficiency target also being met.

    I'm not trying to fix my efficiency -- I'm happy with lower efficiency if it's predictable.

    I am trying to fix my understanding of what happened and what the pre-boil efficiency really is. I must be missing something, because I thought my pre-boil efficiency would be the same as the recipe ending-kettle efficiency given that the measured pre-boil volume and gravity matched the recipe estimates.
     
  6. jeffpn

    jeffpn Well-Known Member

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    I do BIAB. I am only concerned with a kettle batch size target. I set it for 6.5 gallons. My preboil volume is 7.25 gallons when the boil is 60 minutes. I write my recipes for those variables. I don't check gravity until it's in the fermenter. I check my volume from the kettle at flame out. As long as my stick shows 7 gallons, I know I'm at 6.5 gallons, including hot break and hops and anything else that's in my wort. My recipes are mostly set for 75% efficiency. I'm mostly within a point or two on the hydrometer when I check it after chilling.
     
  7. Ozarks Mountain Brew

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    one thing to note your settings will change drastically for deferent size batches, if you set your profile to 5.5 gallon batches then brew a 1 gallon, your settings will be off
     
  8. cassa

    cassa New Member

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    I assume you mean "Default batch size" in the "General Settings" part of the profile? Then, yes, it's set for the same batch size as this recipe (2.5 gal).
     
  9. Ozarks Mountain Brew

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    compare notes to your next brew and report back, things can change from batch to batch good or bad
     
  10. Trialben

    Trialben Well-Known Member

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    Not necessarily cassa. Given your boil off rate any differences in boil length and how vigorously you boil these things change your post boil gravitys. This is how your post boil gravity can differ from your predicted recipe estimate.

    You boiled for 60minutes? If your predicted recipe was let's say 3 Gallons at 1.051 but you achieved 2.5 gallons at the same gravity then this will throw your brew house. You need to increase your sparge amount /pre boil volume to compensate this.

    It will take a few brews at that set volume to really dial it in:).
     
  11. Mark D Pirate

    Mark D Pirate Well-Known Member

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    Boil off rates can change with the weather as well
    First run with my urn was with just water so I could determine boil off and dead space volumes , also hot filled cube to see what chilled volumes I can expect after cooling shrinkage ..my original calcs were off for that run so changed them and had barely any wort left after boil .....
    Nailed it !
     
  12. cassa

    cassa New Member

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    I still don't think my question is clear. I appreciate all the advice and info about improving efficiency and dialing in a process that works. But my question is not about improving efficiency, but understanding how to interpret the Brewer's Friend calculations:

    Why does Brewer's Friend tell me that my pre-boil efficiency is off from predicted when I hit exactly my pre-boil volume with a slightly higher gravity pre-boil wort?
    I don't really care what my pre-boil efficiency is, but the fact that Brewer's Friend told me it was low when I thought it would tell me it was high has me worried that there's something I'm not understanding (or that Brewer's Friend has a bug, which doesn't seem likely).

    I understand that that boil-off rate affects ending kettle gravity, but wouldn't the volume also differ from the estimate, making the ending-kettle efficiency equivalent to the pre-boil efficiency? That's what the FAQ seems to say, and what all the reading I think I've understood seems to say.

    No doubt. I've made 8-10 batches at this volume with this equipment. It's getting a bit more predictable (and I've been lucky that it's all predictably good beer). :) And it's fun. :D
     
  13. Trialben

    Trialben Well-Known Member

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    Forget about ending kettle efficiency go by fermentor volume and calculate your efficiency from this brew house not kettle volume or efficiency. It works for me;).
     
  14. Ozarks Mountain Brew

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    kettle efficiency and preboil gravity is very hard to predict to an exact figure, to many variables that can change it, mostly human error but not always, ball park is a good reading, trying to keep exact records will drive you crazy unless you brew the same beer over and over. I only check my preboil gravity just to prove people wrong that the scrips are wrong because I haven't mist a target preboil gravity in years. now I will get a point or 2 difference in my brew house just because of the yeast mostly
     
  15. Yooper

    Yooper Administrator
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    What temperature did you take your preboil reading? The reason I ask is because if it was taken over about 90 degrees, the reading is notoriously inaccurate, even with correction tables and software. The other thing is evaporation (as it cools) can make the gravity reading inaccurate. If you're using a hydrometer, especially, the reading should be chilled (I use a little pitcher of ice water to chill it quickly, and then take the reading at under 90 degrees and then use conversion software to get the reading). It's not always accurate, but it's pretty close. I normally choose to use my refractometer though because then the evaporation/chilling is not so much of a factor.
     
  16. cassa

    cassa New Member

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    I always chill the sample in a cocktail shaker that I place in a bowl of ice water. The readings are always taken at less than 70 degrees (my hydrometer is calibrated for 60 degrees, but Brewer's Friend makes a temp. correction, usually only affecting the value by one point).
     
  17. Trialben

    Trialben Well-Known Member

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    Hey and as found in another thread by jeffpn trub can scew your readings .
     
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  18. KC

    KC Active Member

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    For BIAB, I noticed that when and where you take the readings have a large impact. At the end of a mash rest, reading from the top is watery because grist has sunk to the bottom. Reading at the end of the boil includes hot break and hops that make for a thick reading. Measurements of wort volume also have a huge impact.

    Inaccuracies in any of these readings, even small ones, will throw off your efficiency calculations. I'd even say that without truly accurate readings, efficiency numbers are useless except for batch-to-batch comparisons of similar recipes.
     
  19. Trialben

    Trialben Well-Known Member

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    Yea for sure. I take readings at same points in all brews. Yea not perfect but you gotta find your happy medium.

    Brew in that happy place :)
     

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