First Partial Mash = Low OG

Discussion in 'General Brewing Discussions' started by Craigerson, Aug 26, 2018.

  1. Craigerson

    Craigerson New Member

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    Hey all. First time posting here and somewhat new to brewing. I've got 3 extract recipes under my belt and wanted to give partial mashing a shot, which I did last night. Researched the bejesus out of this before tackling, and thought I had it all figured out, but I ended up missing my target OG by 13 points and I'm not sure why. Hopefully someone can help me figure this out before my next go.

    Here's my grain bill:

    4# - German Wheat Malt
    1# - American 2 Row
    .5# - Carmel/Crystal 10L
    6# - DME (Golden Light)

    When I plugged these numbers into the BF recipe calculator, I got an OG estimate of 1.050 using a somewhat conservative 60% efficiency (which was my hope). My end result was 1.037 which is an efficiency rate of 30%.

    Here's the process I used.

    I mashed the grains at 152 degrees for an hour, using 6.5 quarts of water. It held at this temp pretty well as I put the kettle in the oven for the full hour. I should mention, I used a 5 gal paint strainer bag in the kettle and mixed up the grains really well. I let the grains drain before doing a batch sparge in another 6.5 quarts of water heated to 180 degrees. My pre-boil volume was about 2.8 gallons, that was before adding my DME (didn't measure my volume at this point - wish I would have). Post-boil volume was slightly over 2.5 gallons. Ended up having 2 quarts of waste in the kettle before going into the fermentor.

    I think those are the key things. I have a feeling I may not have used enough water in the mash, or the paint strainer bags aren't big enough. Would really like to get some feedback from the experts, as I've become somewhat addicted to this hobby, and I don't want to be frustrated when I do my next brew.
     
  2. Nosybear

    Nosybear Well-Known Member

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    First, logically, if your OG was low, you used too much water somewhere, either in the mash or the sparge, or you didn't boil off enough. Can you post the BF recipe or, if you haven't done so, enter your recipe into the Recipe Builder so that we can see the predictions? Given your volume numbers I'm inclined to think you didn't boil off enough water but can't tell from what you've given. An hour boil should boil off about a gallon of water, you boiled off 0.3 gallons.
     
  3. philjohnwilliams

    philjohnwilliams Well-Known Member

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    Did you crush the grains yourself or did your LHBS do it for you? Crush quality is usually the first place I look when there is an efficiency issue. Also, you might try mashing with a little more water, it looks like your water/grain ratio is a bit less than 1.2qt/pound, 1.5qt/pound might work better for you.
     
  4. Craigerson

    Craigerson New Member

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    The LHBS did it for me. Bought it from a pretty reputable place, so I'm trusting they know what they are doing more than I do. What does the increase in water/grain ratio buy you?

    I posted the recipe I used if that will help Nosybear. Regarding the boil off of .3 gallons, wouldn't it actually be somewhat higher then this. I added the 6 lbs of DME to my 2.8 gallons of wort, so I'm thinking it was closer to 3.2 gallons (give or take). Now granted, the boil off was still short of a gallon which may be the problem. I'm boiling on a gas stove, so I didn't have a huge boil, although it was boiling. I assume that could be part of the reason I'm not seeing the full boil off expected?

    Well it doesn't appear that I can post a link to the recipe, perhaps I need to upgrade my membership.
     
  5. Nosybear

    Nosybear Well-Known Member

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    Perhaps. But it looks like you might have solved your problem - boil-off rate. I did my first few batches on a stove and, well, got about the same results as you. I recently switched from a monster propane burner to induction heating and am still trying to get my boil rate dialed in. There are lots of variables in this craft!
     
  6. J A

    J A Well-Known Member

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    #6 J A, Aug 28, 2018
    Last edited: Aug 28, 2018
    None of this is adding up...If you put 6 pounds of DME in 2.8 gallons of water the gravity is 1.090. Even if you diluted that for a regular 5 gallon batch the gravity is 1.050. That's totally ignoring any contribution from other ingredients or any concentration of sugars from boil off.
    There's a lot of missing information here. o_O
     
  7. Trialben

    Trialben Well-Known Member

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    Im not savy with quarts and Fahrenheit and all but you left 2 quarts in kettle as well this will lower brew house as well. Maybe try the cooler route next brew with bag in that way you can get more water volume in there maybe get better conversion/extraction outta ya grains. Also dont be scared to squeeze the bag man there is some gravity points in there as well. Next brew get your measurements recorded use the brewersfriend brew log thats what its there for so you dont have to scratch your head trying to remember what your preboil volume was pluss your gravity boil off fg was extra :).
     
  8. J A

    J A Well-Known Member

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    I think I've deduced your missing information and tracked down your problem. This is a 5 gallon recipe, judging by the ingredients list you noted and you're doing a partial mash/partial boil method. You did a mini mash and added all the ingredients into a 2.5 gallon boil that was intended to be diluted to 5 gallons in the fermenter. The 2 quarts you left in the boil pot (not sure why you'd want to do that) contained a substantial percentage (20% !) of your concentrated sugars. When you diluted to 5 gallons or more, you reduced the gravity.
    Doing the math with just the extract, I come up with 1.038 in a 5.5 gallon batch. There would have been some contribution from your mash but you probably lost more than you think in leaving wort in the boil kettle or diluted more than you think into the fermenter.

    My guess here may be off base but it's the only way to explain how you got the result you did using that much extract. Efficiency applies only to the malt, not the extract, so there's a guaranteed gravity at a certain volume of liquid.
     
  9. Nosybear

    Nosybear Well-Known Member

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    Think of quarts as slightly underfilled liters and fahrenheit, double the celsius and add 30. Neither are exact. Both are unfortunate.
     
  10. Craigerson

    Craigerson New Member

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    All very good information guys. J A - you're correct when you say none of this is adding up, and yes I went with a partial mash / partial boil method. There's one tiny little error from my original post. When I said I added 6# of DME, that should have really said 3# (ok, so that's a big error).

    Regarding the 2 quarts left in the kettle, that was mainly related to the trub, but sounds like I'm being overly cautious in not carrying that forward to the fermentor.

    So summing up what I've learned so far. Sounds like my boil off rate isn't where it needs to be given my gas stove, and I'm leaving far too much wort behind in the kettle. Do most just dump the whole contents of their kettle and not worry about the trub?

    Appreciate the help everyone. Lot's to learn with the new little hobby.
     
  11. J A

    J A Well-Known Member

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    What was your actual fermenter volume when you took the reading that gave you 1.037?
    Did you transfer 2 gallons from the boil and leave 2 quarts and that was that or did you transfer the 2 gallons from the pot and top up with water?
    If you added 3 # of DME to 2.5 gallons of water, absent any other input from mash and no more water, you'd have 1.050 for an original gravity. To get any lower gravity reading, you have to have added less DME or added water.
     
  12. Craigerson

    Craigerson New Member

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    I figured I had slightly over 2.5 gallons after the boil, all went into the fermentor less the 2 quarts. Now that I think about it, that was really stupid on my part to toss out 20% of my wort. I then topped it off with about 3 gallons of water to get to my 5 gallon mark. The gravity reading was taken after the top off in the fermentor.
     
  13. J A

    J A Well-Known Member

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    Ok...now it starts making sense. ;)
    You lost 20 percent of your sugars from your recipe and based on a few quick calculations, your efficiency before that loss was probably in the neighborhood or 60 to 65 percent depending on how accurate your volumes were. If you'd added the water to the entire 2.5 gallons and then left 2 quarts in the pot, you'd have 4.5 gallons of wort at 1.044 or so - much closer to your expected OG
    So the take-away is that your efficiency wasn't off-the-charts low but could definitely stand some improvement. Your mash procedure is probably okay and batch sparging with BIAB can yield good efficiency. As has been mentioned, finer crush for BIAB is pretty necessary and squeezing the bag will get you a lot more sugars.
    After all that work to get sugars in the pot, I wouldn't be leaving anything in the boil pot, especially with partial boil. Get it into the fermenter and top it up. You'll find that your 2 quarts of break material in the boil pot will turn to much less when it's compacted under a layer of yeast at the bottom of the fermenter during cold-crashing. You have the option of using less top-up water if your efficiency isn't what you expect so you can choose a little less finished beer at the proper OG/ABV.
    Onward and upward! :)
     
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  14. Trialben

    Trialben Well-Known Member

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    Second either less top up or sparge water if your not getting a great boil off youll have to reduce mash or sparge volume to account for this orrrr more grain;).
    Boil for longer to reach desired Final Volume. Many options but go with one at a time till youve got all your ducks lined up in a row so to speak.
     
  15. J A

    J A Well-Known Member

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    Boil off won't matter when you're doing partial boil and topping up. Final gravity is determined by amount of water added to the fermenter to achieve volume.
     
  16. Hawkbox

    Hawkbox Well-Known Member

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    Try being Canadian and having to do these conversions on the fly regularly. I fully understood when the Mars recon orbiter smoked into the planet because of a conversion error.
     
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  17. ChicoBrewer

    ChicoBrewer Well-Known Member

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    #17 ChicoBrewer, Aug 30, 2018
    Last edited: Aug 30, 2018
    That has always been a mystery to me. Having a degree in computer science I took many of the same math, chemistry and physics classes engineers take and I never used imperial measures. That was in the early to mid eighties. I don't know why any engineering team would do that. Doesn't make sense. All of the science text books are metric and all of the literature is metric.

    Edit: now that I think about it I started out as an engineering student then switched to CS LOL. It as an exciting time for computing. They used to call it data processing. Used punch cards for my assembly class.
     
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  18. Trialben

    Trialben Well-Known Member

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    Well first option less mash /sparge water
     
  19. Nosybear

    Nosybear Well-Known Member

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    Yep, foot-pounds instead of newtons, or vice versa. A $300,000,000 divot on the surface of Mars, all because the US can't ditch an ancient system of measurement based on the length of some king's appendages. I lived in Germany for a while so am very comfortable with metric units, love them actually, because driving 130 km/h just seems faster.... For quick and dirty, the following conversions work: A meter is a yard with inflation (around 3%). A liter is an overfilled quart. A kilogram is just over two pounds. The Fahrenheit temperature is twice the Celsius temperature plus 30 (thanks, Bob and Doug, for that one).... All I can figure is our units of measure are somehow a barrier to entry to foreign competition in some consumer goods, although we are buying a lot of 16.9 ounce (one half liter) containers these days....
     
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  20. Mark Farrall

    Mark Farrall Well-Known Member

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