Brewhouse efficiency way lower than mash efficiency

Discussion in 'Beginners Brewing Forum' started by kkourmousis, Apr 4, 2021.

  1. kkourmousis

    kkourmousis Member

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    Hey guys.

    This is the 2nd time that this happens to me (in a total of 4 batches I have done so far) and I can't figure this out.

    I am starting with ~75% mash efficiency and my brewhouse efficiency ends up ~65% !

    Pre boil vol. 13.87L, pre boil gravity 1.046
    Post boil vol. 7L, post boil gravity 1.074
    Boil time was 108min (baby woke up and I wend 20 mins behind from intended 90 min boil).

    What am I missing here?
     
  2. Sunfire96

    Sunfire96 Well-Known Member

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    #2 Sunfire96, Apr 4, 2021
    Last edited: Apr 4, 2021
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  3. kkourmousis

    kkourmousis Member

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    I see. Thank you !!
     
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  4. Sunfire96

    Sunfire96 Well-Known Member

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    No worries! The recipe FAQs is a great resource
     
  5. Sunfire96

    Sunfire96 Well-Known Member

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    65% is a respectable brewhouse efficiency BTW, but for mash efficiency, 75% is a tad lower than what you could theoretically be getting.

    The actual brewhouse efficiency number is not as important as having a consistent BE. It's more difficult to plan recipes and predicted gravities and IBUs if the BE changes drastically from batch to batch.

    My first few months of brewing I had wildly inconsistent efficiency and sometimes made a beer with 1.040 OG and sometimes made a beer with 1.065 OG when I was shooting for 1.050. Over time I've dialed in the small steps that cumulatively increased my BE to 70%. There are additional steps I could take to increase it further if I'd like, but it's nice having consistency for now.

    If you have any more questions, please feel free to ask! :)
     
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  6. dmtaylor

    dmtaylor Active Member

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    Something is wrong in your numbers. The numbers above are impossible. One or more are not accurate. Sugar does not boil off. Hence, pre-boil gravity points, 13.87 times 46, must equal post-boil gravity points, 7 times 74. But they don't.

    So... maybe you had a boiloff and lost a lot of sugar that way? Or maybe your gravity measurements were made at hot temperatures to where you actually had different gravity numbers for pre or post boil? Or maybe one or both of your volume measurements are very inaccurate? Maybe you left a LOT of trub behind before taking the final volume measurement? You need to include it. Take a look, this should be the key answer you were seeking, or at least a big part of it. And when is the last time you calibrated your hydrometer in plain water? If that's off by a few points, that could also contribute.
     
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  7. Hawkbox

    Hawkbox Well-Known Member

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    Also 65% final efficiency is a little low but nothing major.

    You already know how the different stages get different efficiencies so your next step would really be to make notes on what you leave behind where and start tracking the steps a little closer.
     
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  8. kkourmousis

    kkourmousis Member

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    Yes this is what I am planning to do.

    I agree with you. I believe I should stop experimenting with different sparge methods and find one and stick to it. Other than that I don't change a lot

    That was my thoughts exactly! Let me answer to each of your questions:

    No boiloffs

    Pre boil gravity measurement was made at hot temperatures but I used Hydrometer calculator. Also, I kept the samples and checked them out once they were cool and I got what I was expecting from the Hydrometer calculator. Post boil gravity measurement was made at a quite cooler temp.

    Volume measurements is what could easily be off. I have to resign on initial water measurements (I know how much water I put in) and calculate how much is being absorbed. At this point I also measure the height of the water in the kettle and calculate the volume (height*π*r^2). If there is an error, it is there but I can't figure it out

    I did not leave any trub behind, I had minimum. I don't know if this is normal but I never do. Maybe I should let the beer settle before transferring to fermenter

    Good point on that plain water calibration of the hydrometer, I will start with this
     
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  9. Donoroto

    Donoroto Well-Known Member

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    @kkourmousis Mark the inside of the kettle with volume measurements. Add a liter, scratch a line; repeat until the top. Maybe start at 3 liters.

    I have this 'electric engraver', a hard metal point with a vibration motor behind, that marks metal easily. You can probably think of something.
     
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  10. Sunfire96

    Sunfire96 Well-Known Member

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    #10 Sunfire96, Apr 6, 2021
    Last edited: Apr 6, 2021
    I used a sharp deck screw. You could also sacrifice a wooden spoon or dowel
    20210406_073034.jpg
     
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  11. dmtaylor

    dmtaylor Active Member

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    FYI, I meant to say "boil-over" but I believe you understood what I meant.

    I'd take a hard look at volume measurements. The more accurate you can be on volumes, the better you will understand what's going on and be able to be more predictable on future batches. Temperatures also matter. Volume at 200 F is not the same as volume at 65 F, there is some shrinkage as it cools. So correct any hot volumes to what they would be at cool temps. Software and spreadsheets can help with this. The shrinkage factor I use is like 0.96. Small effect of about one quart in a standard 5 gallon batch, but it's still an effect that can matter. Eyeballing or guesstimating a volume measurement = not good enough.
     
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  12. RustyBeer

    RustyBeer Member

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    i'm not calculating it but the gravity numbers seem plausable given a 108min boil. if you over boiled , you lost water and the gravity went way up. did you add water to the fermentor to make up for lost volume to hit a volume mark? the only way i can see your FG going way down is if you added too much water.
     
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  13. kkourmousis

    kkourmousis Member

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    Yes I diluted it. My kettle is medium sized so I always have to dilute in order to have a normal size batch
     
  14. dmtaylor

    dmtaylor Active Member

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    Ah.... so is it possible that your actual post-boil gravity was 1.091 but then you watered it down to your reading of 1.074?

    Or to look at it another way, when you measured 1.074, did you really have 7L or was it more like 8.6L because you watered down with an extra ~1.6L?
     
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  15. kkourmousis

    kkourmousis Member

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    I really appreciate your interest in this, so let me explain in detail:

    Strike water was 9L, this was measured.

    Grain was 2.7kg and it should have absorbed 1.8L and it then should be 7.2L (estimate)

    I sparged with 6.8L (measured) and it should then be up to 13.8L (estimate)

    I took a hydrometer reading at the time, it was 1.034 @ 55.5 C, which ends up in a calibrated 1.045 pre boil gravity. This was also measured once it was cooler and it was precise.

    So pre-boil volume = 13.8L (estimate) and pre-boil gravity 1.045 (precise). So far, all according to plan.

    After 108 minutes of boil, my kettle should have lost 6.8L. So post boil volume should be 7L (estimate)

    I took hydrometer reading at that time and it was 1.072 @ 26 C, which ends up in a calibrated 1.073 post boil gravity. This was also measured once it was cooler and it was precise.

    I then diluted my wort with 5L (measured) of water, and this should bring the volume up to 12L (estimate). Once I transferred the wort into the fermenter, I saw it was indeed 12L. Because the 5L addition was measured, this means the estimate of my post volume was actually precise as well!

    I took a final hydrometer reading at that time and it was 1.045 (calibrated).

    So, post-boil volume 7L (precise) and post-boil gravity 1.073 (precise) and
    post-dilution volume 12L (precise) and post-dilution gravity 1.045 (precise)

    The only volume for which I can't be sure is the pre-boil volume. This leaves room for:
    • grain absorption miscalculation
    • boil off losses miscalculation
    But are these enough to explain the odd numbers?
     
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  16. RustyBeer

    RustyBeer Member

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    #16 RustyBeer, Apr 9, 2021
    Last edited: Apr 9, 2021
    Seems normal. What was your target finishing gravity? High gravity in the mash after conversion, it went down after sparge because you added more water with less sugar concentration. It went Way up after too long of a boil because you boiled off a lot of water, not sugars. It went Down at fermenter because you diluted it with more water. Make a dipstick or kettle markings so you know you’re preboil volume.
     
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  17. Donoroto

    Donoroto Well-Known Member

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    I agree, all seems good.

    First, 7.2 + 6.8 = 14, not 13.8. But 200 ml is not a lot, certainly not enough to worry about.

    Second, as your child grows older, they need to understand that Daddy's boil should not have to be extended unnecessarily. :rolleyes: :p
     
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  18. dmtaylor

    dmtaylor Active Member

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    I guess I enjoy problem solving. So I have completed a lot more number crunching to try to determine the most likely source of error, as these numbers cannot possibly all be accurate. Here is what I have come up with.

    The most likely error might be your preboil temperature. If preboil temp was actually 35 C instead of 55.5 C, you would have preboil gravity of 1.038 instead of 1.045 (corrected for room temperature from 1.034 to 1.038). From this point, all of the math works out pretty well, with minor adjustments. I was able to figure out the most likely actual numbers, allowing for minor margins of error for each data point. Given the preboil gravity of 1.038 instead of 1.045, if the following data were most accurate, then everything works out:

    Grain absorption was not 1.8L but rather 2.3L. This leaves (9 - 2.3) = 6.7L from the first strike.

    Sparging with 6.8L gave you a total 13.5L preboil volume (not 13.8L). The SG here then was 1.038 @ 13.5L as corrected for room temperature.

    Boiloff rate was about 25%, taking the volume down to 7.4L.

    Important: At this point, shrinkage occurs due to the boil temperature cooling down to room temperature. This results in a loss of about 0.3L, taking the volume down to 7.1L. Gravity at this point was measured to be 1.073 which appears to be pretty accurate, or perhaps was 1.074.

    From here, you then diluted with 5L more to about 12L, with a gravity of about 1.044 (perhaps a point lower than your 1.045). Tiny errors of 0.001 like this seem insignificant but can make some difference in the end. More significant perhaps might be any volume losses, if you lose a cup or two of volume here & there, it can throw off some of the readings.

    So now... what does all of this mean? Well... honestly..... not a whole lot maybe! It just looks like something was messed up with the preboil gravity or temperature measurements, causing additional confusion. With some number crunching, it shows how tiny errors can make a difference.

    But the real bottom line, as far as efficiency goes.....

    Yes, you only got about 65% brewhouse efficiency. But so what! To some extent, this should be expected for high gravity beers and/or concentrated boils. You had a high gravity mash and boil that went to 1.073-1.074 by the end of the boil. That will tend to hurt efficiency unless you sparge more to collect more sugars. Otherwise, higher gravity beers will tend to give you lower efficiency. It's just part of the nature of high gravity brewing. If you want to improve your efficiency, you can try a few different things:

    1) Mill the grains harder. This can improve efficiency by as much as 10-15%. It really helps a lot.

    2) Sparge more, and boil longer. The more you sparge, the more sugars you collect. And you can always boil longer to achieve a higher gravity. Combining a bigger sparge and longer boil, you can easily have 75-80% or more brewhouse efficiency with higher gravity brews. Something to keep in mind for future batches.

    3) Don't concentrate the boil and dilute later. The water you added at the end of the process, if added to the sparge instead, would have collected more sugars.

    Hope this helps. If not, oh well, I just enjoy mathematics a lot. Yeah I'm kind of weird. Cheers.
     
  19. kkourmousis

    kkourmousis Member

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    Well that was just amazing!

    Unfortunately, one assumption is not correct: the pre-poild (post-mash) gravity was double checked, I let it rest for the temperature to drop down to 30ish Celcius and it was actually 1.045

    On the other hand, grain absorption being higher that I was expecting is a pretty good assumption.

    As you said, errors of 0.001 are playing a role here for sure, but I am taking measurements with hydrometer so errors of 0.001 are definitely a possibility.

    I am buying my grains milled, I do not have a mill yet. As for the dilution, I can't always avoid it. My kettle is only 17L (to the top) so I only have room form 15.5L pre-boil volume. If I want to end up with more than a 10L batch, I have to dilute it. Alternative is to use DME but I prefer not to do so

    I will gladly sparge with more water, I was not sure about the ratio I should maintain. You see, I have 2.7kg of grain here and I think I am supposed to use at least x2.5 as strike water. Because I am not sure, I always use a bit more, so instead of 7L, I used 9L as strike water. I could definitely use those extra 2L for sparging, as long as the x2.5 grain to strike ration is correct.

    As for the sparging itself, I have a secondary 9L kettle which I use. I drain and then place the grain on a colander above the main kettle. I then slowly drop as much of the sparge water I feel I can, so as for the remaining to be able to accommodate the grain bag. I probably end up with 3L in the secondary kettle, where I place the grain bag and I leave it there for about 5 mins.

    Yep, that's the plan for sure

    Hahaha AMEN
     
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  20. RustyBeer

    RustyBeer Member

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    For the record, “you’re “ was a typo.
     
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