Refractometer readings

Discussion in 'General Brewing Discussions' started by Zambezi Special, Sep 29, 2022.

  1. Zambezi Special

    Zambezi Special Well-Known Member

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    Most refractometers have automatic temperature compensation, but how accurate is this?
    Let's say the wort is at room temperature and that is 40 oC (104 oF). Will the reading be accurate? Or do you use a table like for hydrometers and adjust?
    And if it is cold? Say 10 oC (50 oF)

    Inquiring minds want to know (and check a couple of calculations)
     
  2. Herm brews

    Herm brews Well-Known Member

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    I notice with my ATC (auto temp correct) refractometer that readings shift. A hot sample of wort usually reads lower, then higher as it cools. The variation is slight, but it exists. One cool feature of my refracto is measurement in both Brix and specific gravity. So with unfermented wort, I can see that my hydrometer and refractometer are in synch, which leads me to use the refracto for most measurements. However, I always pull a hydro sample for Original Gravity, and cross check with my refracto.

    Assuming you have both hydro and refracto, have you checked them against each other? Have you worked out a wort refraction index (WRI) for your refracto? Having the WRI is very helpful when it comes to using the refracto to measure for final gravity, as there is no waste.

    In other words, there is some variability with refractometer readings with respect to temperature, but those variations are much smaller than with hydrometer.
     
  3. Minbari

    Minbari Well-Known Member

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    Unless you are trying to read it instantly, this is really not a huge issue. Most are calibrated at 60F. By the time you put the 1mL of liquid on it and raise it to your eye, it has cooled.
     
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  4. Minbari

    Minbari Well-Known Member

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    I would disagree with the last part, with some explanation.

    A hygrometer requires a larger sample. This sample will remain at whatever temp it was for much longer than the 2drops on a refractometer.
    A hydrometer that is calibrated for 60F and then read at 90F one day and 70F the next will read different.

    Mine would be 4 pts different at that spread. So just make sure you adjust for it
     
  5. Zambezi Special

    Zambezi Special Well-Known Member

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    But that's exactly the point.
    The refractometer is calibrated for 60 F (mine is for 68 F (20 oC)) but mostly, my liquid will not be at that temperature and not get to it as the temperature inside and outside my house is much higher. Currently we are talking around 100+ F inside and outside (at day time)

    So, do I compensate for this reading?
    I got tables for the compensation for hydrometer, but have not seen one for a refractometer
     
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  6. Trialben

    Trialben Well-Known Member

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    I put the pipette in the glycol tank and swirl it for a few seconds before delivering the sample to the refractometer.
    Such a small volume cools incredibly quick.

    Maybe you could pop yours in the freezer for a bit to cool sample before measuring.
     
  7. Nosybear

    Nosybear Well-Known Member

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    ATC simply compensates for the difference between the sample and the stage. You still need to let the sample cool for a few moments before testing it - you can see (as Herms pointed out) that the reading changes, generally increases, by a point or two over time. No need to cool anything, air will do a good enough job in a minute or two.
     
  8. Sunfire96

    Sunfire96 Well-Known Member

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    Ah, I think I get what you mean...how will your sample ever cool to 68F when it's 100+F degrees ambient. I would try to cool your sample and compare the reading to a non cooled sample. My guess is the difference is less than 5 SG points. Definitely noticeable if you did nothing to compensate
     
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  9. Minbari

    Minbari Well-Known Member

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    Definately an issue. I would do as @Trialben Suggested. Put the sample in the fridge for a minute and chill it slightly.

    Other than that. You could make a table. Take a refrac at a temp with a hydro reading along side and see what correction you need to make. The temp correction might track with the hydro correction or it might not
     
  10. dmtaylor

    dmtaylor Well-Known Member

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    It's only accurate at 40C (104F) if calibrated with plain water at 40C (104F). Otherwise the ATC thing doesn't do shit.
     
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  11. Trialben

    Trialben Well-Known Member

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    So what your saying dmtaylor is if you calibrated you refractometer to 0 at 40 centigrade than you measurement of wort at or around that same temp should be correct?

    Makes sense to me.
    I do see 20c as the calibrated temp on my refractometer when I look through it but hey what's a brix or two? 2 sg points I'm not sure?
    I ain't done the maths.


    I'm new to the refractometer BTW only had one for maybe 5 brews now.
     
  12. Minbari

    Minbari Well-Known Member

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    in general I would say that is true, within reason. if you calibrate it for 10C it would be acurate for that temp. calibrate for 40c it would be acurate there.
     
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  13. Donoroto

    Donoroto Well-Known Member

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    ...or put the refractometer in the cool box to get it closer to 68 F?
     
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  14. Zambezi Special

    Zambezi Special Well-Known Member

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    What I've done sofar, is take the refractometer, work back to SG.
    Then grab the SG temperature correction table and correct the SG value.
    But I got no idea how accurate this is.

    I suppose I'll have to start doing more readings. Maybe a small small batch dedicated to hydro & refracto readings several times a year (for temperature effect)
     
  15. Zambezi Special

    Zambezi Special Well-Known Member

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    Going to do this just before next brew or bottling section.
    No, make that "as is" for next bottling. Then calibrate for current temp and measure again!
    I'll definitely report back on this as it sounds like a real easy solution
     
  16. Zambezi Special

    Zambezi Special Well-Known Member

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    Update:
    36 oC for both young beer & water
    Refractometer first reading: 4.5
    Calibrated with water. Not much adjustment necessary, new reading 4.5 to 4.75
    I kept the sample to try again early morning, when it is cooler.

    Hydrometer reading: 1.002-1.0025
    But I got 2 hydrometers
    Hydro 2 reading 1.000 :eek:

    I will repeat with unfermented liquids.
     
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  17. CoFlyGuy

    CoFlyGuy Well-Known Member

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    I was recently flipping through my Brewer's Notebook and found a spreadsheet I had downloaded for correction on my ATC. Anyway, I tried it out and it worked.

    Check out this form and the accompanying recipe. Definitely helped me out with getting things dialed.

    Check out the Refractometer Calculator here on Brewer's Friend. There is a really useful spreadsheet available in excel format to help you out.

    Hope this gives you something to work with.

    Brew on my friend!
     
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  18. Nosybear

    Nosybear Well-Known Member

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    I use a homemade spreadsheet implementing the formulas found in a past issue of Zymurgy. Because of the ease of reading the refractometer, I find it more accurate than using my hydrometer.
     
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