Author Topic: More refractometer woes  (Read 2293 times)

Offline ccfoo242

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More refractometer woes
« on: April 09, 2012, 11:34:03 AM »
I bought a refractometer because I thought reading the hydrometer was too difficult, but either I have a crappy device or I'm using it wrong because I can't seem to get consistent readings.

I'll calibrate with distilled water...0.0 brix
Take a wort sample...15.5 brix
Hmm...take another sample...16.5...16.0...16.2...
Check distilled water...still 0.0.

WTF?

I finally take a large enough sample for a hydrometer and get 1.065, exactly what it should have been.

I took readings after the wort settled and after it was stirred up, always different. I rinse the surface of the refractometer with a little distilled water between readings and dry it with a clean cloth.

What am I doing wrong?

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Offline bluesman

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Re: More refractometer woes
« Reply #1 on: April 09, 2012, 11:50:23 AM »
A couple of things to consider when reading a refractometer.  Be sure to keep trub or hop particles from getting underneath the daylight plate as they can skew the reading.  Assure that the wort sample is a representative sample.  The temperature of the wort can also have an affect on the sample, as a boiling or very hot wort can affect repeatability because the wort will evaporate during transfer to the prism.  Once the hot wort sample has been transferred and the daylight cover closed, allow at least 30 seconds for the wort temp to stabilize. 

These steps as well as taking multiple readings will give you an average sugar concentration. There can be a slight deviation depending on the amount of solids that are still in suspension and the ability to get a representative sample.
Ron Price

Offline majorvices

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Re: More refractometer woes
« Reply #2 on: April 10, 2012, 04:39:06 AM »
Yeah, in your case you are not letting the wort temp stabilize. It took me a while to finally learn to be patient enough to take a proper reading. I have been taking my reading with a large spoon and blowing on that to cool it down quickly, then dropping it on the glass, blowing again and then closing the lid and blowing yet again then wait a few seconds. Problem solved.

That said, I have given up trying to get an FG reading from it. The calculation never seems to work. I'm assuming you have to have a crystal clear sample to get a correct reading.
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Offline mabrungard

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Re: More refractometer woes
« Reply #3 on: April 10, 2012, 05:03:06 AM »
I second the wort cooling issue.  Even though many refractometers have 'ATC', it doesn't seem to work when the temperature is above 100F. 

I grab my sample of hot wort with a plastic micro dropper.  I'm sure the wort temperature is still way over 100F when I put two drops on the window.  I'm careful to avoid trapping any air bubbles when placing the drops or when closing the cover plate.  I notice that my readings rise as the wort cools further on the window.  I typically see the measurement rise 2 or 3 tenths of a Brix as it cools.
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Offline ccfoo242

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Re: More refractometer woes
« Reply #4 on: April 10, 2012, 05:24:31 AM »
Alright maybe that's it. I've been using little plastic pipettes to pull samples. I'll let them sit a few minutes before reading next time. I'll keep using the hydrometer until I'm sure that I'm sure that I'm doing it right!  :P

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Offline tschmidlin

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Re: More refractometer woes
« Reply #5 on: April 10, 2012, 09:13:13 AM »
I second the wort cooling issue.  Even though many refractometers have 'ATC', it doesn't seem to work when the temperature is above 100F. 

I grab my sample of hot wort with a plastic micro dropper.  I'm sure the wort temperature is still way over 100F when I put two drops on the window.  I'm careful to avoid trapping any air bubbles when placing the drops or when closing the cover plate.  I notice that my readings rise as the wort cools further on the window.  I typically see the measurement rise 2 or 3 tenths of a Brix as it cools.
I suspect the rise you are seeing is due to water evaporating from the hot sample.  I haven't tested that hypothesis, but I cool my sample in a covered cup before measuring.
Tom Schmidlin

Offline euge

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Re: More refractometer woes
« Reply #6 on: April 11, 2012, 10:46:00 AM »
Usually I dip something in the wort- a temp probe or a spoon and immediately place a drop on the lens and then flip the cover. I let it cool a bit- as it's a drop or so it cools rapidly, usually within seconds. The temp and evaporation problem is solved by doing it this way.



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Offline bluesman

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Re: More refractometer woes
« Reply #7 on: April 11, 2012, 11:33:46 AM »
Usually I dip something in the wort- a temp probe or a spoon and immediately place a drop on the lens and then flip the cover. I let it cool a bit- as it's a drop or so it cools rapidly, usually within seconds. The temp and evaporation problem is solved by doing it this way.

This  ^^^^ is my method as well. 
Ron Price

Offline mabrungard

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Re: More refractometer woes
« Reply #8 on: April 11, 2012, 11:58:51 AM »
I suspect the rise you are seeing is due to water evaporating from the hot sample.  I haven't tested that hypothesis, but I cool my sample in a covered cup before measuring.
Shouldn't be the case with the cover plate closed. But could be.
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Offline tschmidlin

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Re: More refractometer woes
« Reply #9 on: April 11, 2012, 12:03:22 PM »
I suspect the rise you are seeing is due to water evaporating from the hot sample.  I haven't tested that hypothesis, but I cool my sample in a covered cup before measuring.
Shouldn't be the case with the cover plate closed. But could be.
Maybe not.  It should cool pretty quickly when spread out on the lens, maybe there's not enough time for significant evaporation.
Tom Schmidlin

Offline a10t2

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Re: More refractometer woes
« Reply #10 on: April 14, 2012, 09:31:32 AM »
I've seen bubbles form in between the lens and cover plate when I'm testing a hot sample. Letting the sample cool in a sealed container seems to give me good consistency.
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