Display fermentable sugar contribution in PPL / Pre-boil gravity wrong

Discussion in 'Recipe Editor' started by Baboonanza, Oct 10, 2019 at 10:12 AM.

  1. Baboonanza

    Baboonanza New Member

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    Is there any way to do this? I have everything set to metric so it's a bit weird to have the contrinutions shown as PPG.


    Ihe reason I noticed this is that I wanted to double check my pre-boil OG because I just brewed a recipe where I was 5 points under the predicted pre-boil gravity, compensated with some malt extract then ended up with OG exactly 5 point over.
     
  2. Nosybear

    Nosybear Well-Known Member

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    Don't you want points per KG per liter? Mixing pounds and liters is something so specialized I don't think it's a good idea to try to implement (in other words, stick with one set of units, says the guy who regularly measures his hops in grams). As far as the OG: Check your instrument (refractometer or hydrometer) first, it's the most likely cause of the error. After that, well, you aren't the first to report a pre-boil gravity problem. I've had it with very big beers but the software can't anticipate every brewing scenario. I adjusted my efficiency and the next batch came out perfectly.
     
  3. Pricelessbrewing

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    @Baboonanza can you link to the recipe, and list he measurements you took? Volume, gravity, and temperature.

    Preboil gravity, it's possible it's an issue of unit conversion but I manually checked the preboil gravity yesterday (in lbs and gallons) and it's working as it should.

    However that is with cooled volumes, if you're working from hot volumes then you'll generally be off by about 4%.


    Generally points /kg / L isn't a standard unit. Us homebrewers use PPG, pro's use % extract (vs succrose). Non us Brewers generally use % extract with a smaller minority using PPG still for malt potential. It's an easy calculation to switch to also supporting PkgL but it's not very common.
     
  4. Baboonanza

    Baboonanza New Member

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    Yes, I mean KG / L as PPL would be nuts :)

    I appreciate it's not that common but given I'm a metric brewer and not even in the US using US gallons for measuring anything is pretty foreign to me (pardon the pun). Anyway, it's obviously not a major issue as the maths can be done I just thought it odd.

    The recipe is here: https://www.brewersfriend.com/homebrew/recipe/view/881890/chocolate-milk-stout

    I'm a fairly new AG brewer and I hadn't bothered taking pre-boil readings before. My measurements were:
    pre-boil 1.037 at 31C (corrected to 1.039), expected from recipe was 1.044
    OG 1.057 at roughly 20C (including about +0.005 from a late DME addition)

    I guess that either my thermometer or my hydrometer (or both) were slightly out. I wouldn't have been suprised if my efficiency was out but I was suprised that the pre-boil was low while the final OG would have been spot on without the late addition. Or given there are multiple late additions in the recipe maybe the pre-boil is accurate and the late-additons messed up the final OG prediction. I'll have to try with a simpler recipe!

    Thanks for your help
     
  5. Nosybear

    Nosybear Well-Known Member

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    I don't know why we hang onto our obsolete system of measurement based on weird multiples of the length of some dead king's feet. But we do. I saw PPL and had horrific visions of some new bastardization of measuring systems involving cubits, pecks....
     
  6. Pricelessbrewing

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    There's some weirdness going on with the recipe, as the preboil is the same size as the batch size? Are you adding 2 Liters after the boil?

    Gravity readings should never be temperature corrected, it's not very accurate. Best practice is to take a sample and let it cool naturally then take the reading.

    Whenever you're going to attempt an efficiency calculation, or gravity prediction/correction, you must take the volume measurement and temperature measurement. Then you can do a rough approximation for the cooled temperature (there's a temperature adjustment calculator on my website). If it's at boil, then it should be approximately 4-4.4% for thermal expansion.

    With the sugar boil additions, it's also hard to estimate and make adjustments as they will increase the volume as well as the gravity.

    But my best guess based on your recipe, at a preboil volume of 21L (21.92L @ boil), and 70% brewhouse efficiency the preboil gravity (using only the grains) should have been ~1.0439 SG. This lines up with brewers friends calculation of 1.044
     

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