Brew session refractometer calculations are completely wrong

Discussion in 'Brew Sessions' started by Baron Swank, Dec 9, 2013.

  1. Baron Swank

    Baron Swank New Member

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    I have a problem with the way "brew session" handles brix readings.
    Batch1: 1.091 OG.
    after 3 weeks, fermentation had ceased and I measured FG at 17Brix. According to the calculations on this site, my FG is 1.102!!! According to this site http://www.northernbrewer.com/refractometer-calculator/, my FG is 1.054, which is the same as my hydrometer reading. This batch failed to finish fermentation, but that is not the point.

    Batch2: OG 1.078. With this one I did my FG measurement as usual, entered the brix value, and it returned a value of FG1.009. I thought it was fine, and bottled the batch. 2 weeks later I tried the first bottle. That's definitely not FG 1.009. More like 1.030 or 1.040 I reckon. I wish I had given this beer a taste before bottling, even when the values returned by my brew session said it was fine...

    Am I doing something wrong here? Northernbrewer's refractometer calculator gives me the same values as my hydrometer. brewer's friend does not...
     
  2. Ozarks Mountain Brew

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    Re: Brew session refractometer calculations are completely w

    have you set up your equipment settings correct, everything changes based on those settings and your efficiency settings, your ending gravity is really just a calculation under perfect conditions, that can change drastically by a number of factors
     
  3. Baron Swank

    Baron Swank New Member

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    Re: Brew session refractometer calculations are completely w

    No matter how wrong my equipment settings might be, fermenting my wort from 22Brix to 17Brix should never result in an INCREASE in gravity. Inaccurate equipment profile can not account for an error of this magnitude.
     
  4. Ozarks Mountain Brew

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    Re: Brew session refractometer calculations are completely w

    we would have to know more, recipe and everything that went in to the beer including all sugars and yeast amounts, and how it was brewed this is a high gravity beer and allot can happen in real time to change the results
     
  5. Baron Swank

    Baron Swank New Member

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    Re: Brew session refractometer calculations are completely w

    Please, this has nothing to do with my brew!!

    Try it for yourself:
    1. pick ANY recipe from your list, and press "brew" to start a new brewing session. Don't deduct anything from your stock; this is just a test

    2. click "brew log", click "add log entry". Create a log entry for "brew day complete". Leave the date field open, set volume to 50L and Gravity: 22 Brix (refractometer), record to log in SG. The value gets correctly recorded to the log as SG 1.092

    3. Add another log entry called "sample", "racked" or "fermentation complete"; Final gravity: 17brix, correction factor: 1, alcohol correction: 1.092. Record to log as SG.

    Result: 1.101 SG. This result is WRONG. The correct result is 1.054 SG, as reported by my hydrometer AND the calculator at northernbrewer.com. (my fermentation has stopped too early, but this is not the point)

    The calculation produces a result that would be physically impossible to achieve, and this has nothing to do with what went in the beer!!
     
  6. Ozarks Mountain Brew

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    Re: Brew session refractometer calculations are completely w

    OK now we narrowed it down, wasn't sure where in the site you were looking first, will have to let Larry get this one, haven't seen him post in a while but I'm sure he'll get back to it
     
  7. RoundKid

    RoundKid New Member

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    Re: Brew session refractometer calculations are completely w

    From reading the source material for the refracomoter alcohol correction formula used by this site (http://seanterrill.com/2011/04/07/refra ... g-results/) it appears this is a known issue and the formula does not provide acurate readings below 50% attenuation. Your fermentation stopping early is part of the point. Northern Brewer's formula correlates better across the whole spectrum (which is why it worked in this instance), but is less accurate within the range (60-90% attenuation) that is most useful to brewers.

    From you second beer, it is hard to say if the formula is the issue without a corresponding hydrometer reading rather than just your tasting results. Did you decarbonate a bottle and take a hydrometer reading to confirm what you were tasting was a high finishing gravity and not some other perceived sweetness?

    Additionally, have you determined the wort correction factor for your particular refractometer? http://www.brewersfriend.com/how-to-det ... on-factor/

    You seem to be using the 1.00 factor, but based on my use, the article above, and reading on seanterrill.com it seems that 1.04 is more acurate; but the best thing to do is test your own equipment over several brewdays/beers before trusting the results of your refractometer alone.
     
  8. LarryBrewer

    LarryBrewer Active Member

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    Re: Brew session refractometer calculations are completely w

    Personally, I use a refractometer for mash gravity readings and pre-boil gravity. I find a hydrometer better suited for FG since it reads true in all cases (provided the hydrometer reading is temperature corrected). As you and others have noticed, refractrometers are poor at measuring FG since the alcohol content throws off the reading. An FG reading from a refractometer should really be considered an estimate. Use a hydrometer for a solid figure.

    RoundKid correctly points out, this site uses the Sean Terrill equation. 50% attenuation is something the equation doesn't handle too well apparently.

    In my own testing using my PAL-1, the Sean Terrill equation lined up better than other equations. This low attenuation situation is way outside the range of a typical brew. Especially considering Sean Terrill is a pro brewer, he must have tailored the equation to a tighter attenuation range to make it more accurate. So, once your attenuation improves everything else falls into place.
     
  9. Baron Swank

    Baron Swank New Member

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    Re: Brew session refractometer calculations are completely w

    this makes sense!

    in the case of the other beer: I decarbonated a sample and checked. It appears that I made a mistake reading my refractometer. The FG for this batch is 1.022. 10.8 Brix. In this case, both refractometer calculators give a result of 1.025, which is well within reason, considering that I've made no attempt calibrating anything.

    Thanks for your help!
     

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