refractometer accuracy and ???

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spencoid
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refractometer accuracy and ???

Post by spencoid »

i like the idea of testing the output of my still to get an idea of what the reflux ration is doing to the output strength etc etc. i do understand that the vapor temp at the top of the column should directly relate to the alcohol strength but thought that a refractometer would be a cool tool to add to my collection.

i got a cheap one ($20 amazon) which miraculously arrived in an open bag yesterday so i guess someone was looking after my interests :)

i measured several mixes i have and compared the reading to the reading of a standard float hydrometer. this is also a cheap device but when i got it i checked it against accurate specific gravity measurements. i have a little volumetric flask which makes it easy to accurately measure a fixed volume and i have an old analytical balance accurate to a half milligram or so. i convinced myself that the float hydrometer is quite accurate if temperature compensated properly.

i understand that the refractometer is measuring the refractive index and that it is not measuring alcohol strength directly and can be influenced by the presence of any material with a different refractive power that might be in the mix. so i am not expecting (like the idiot on amazon who reviewed this same refractometer and gave it two stars because it did not perform magic) this thing to sort out the alcohol strength in a complex mixture.

that said, here is what i don't understand.

cheap Amsterdam vodka and gin both read close to the 40% which matches their 80 proof. Some alcohol i made a while ago and remember as being about 186 proof puts the meter off the scale. So far so good. Gin i just made measures 62% with the hydrometer but 58% on the refractometer. Not so strange, maybe the juniper etc is stronger in my gin or maybe it is the high mineral content of my water.

the big strangeness is that 192 proof alcohol (everclear from Mexico) measures correctly on the hydrometer but on the refractometer it is totally out of line. It shows 65% on the refracto but should be off the scale. The only explanation i can think of is a little scary but good justification for making my own alcohol. Could the Mexican alcohol be contaminated with other alcohols such as methanol? Would methanol lower the reading of the refractometer. Water is 1.333 RI ethanol is 1.36 and methanol is 1.33 so this is possible but wouldn't it take a lot of methanol to have this much effect on the reading? are there other contaminants that could cause this much change? lead arsenic etc?
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kiwi Bruce
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Re: refractometer accuracy and ???

Post by kiwi Bruce »

One of the things I found with my amazon El Cheapo refractometer is that it has to be zeroed before each use, using distilled water, there is a small screw on top to adjust it. I don't have the instructions sheet in front of me at the moment... as I remember it's pretty simple. My El Cheapo beer wort refractometer, on the other hand, has been bang on since day one...go figure.
Last edited by kiwi Bruce on Fri Jul 07, 2017 3:29 pm, edited 1 time in total.
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kiwi Bruce
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Re: refractometer accuracy and ???

Post by kiwi Bruce »

spencoid wrote:the big strangeness is that 192 proof alcohol (everclear from Mexico) measures correctly on the hydrometer but on the refractometer it is totally out of line. It shows 65% on the refracto but should be off the scale. The only explanation i can think of is a little scary but good justification for making my own alcohol. Could the Mexican alcohol be contaminated with other alcohols such as methanol? Would methanol lower the reading of the refractometer. Water is 1.333 RI ethanol is 1.36 and methanol is 1.33 so this is possible but wouldn't it take a lot of methanol to have this much effect on the reading? are there other contaminants that could cause this much change? lead arsenic etc?
I strongly doubt there would be anything "wrong" with Everclear from Mexico...any meths would have to be deliberately added...not likely. More likely however is "user error" with the El Cheapo Amazon refractometer...I only have to look in the mirror to see one of these.
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bitter
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Re: refractometer accuracy and ???

Post by bitter »

refractometer are good for measuring og... but not much good for fg... I have a couple .990 to 1.020 hydrometers I use to measure fg.

B
spencoid
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Re: refractometer accuracy and ???

Post by spencoid »

what are og and fg?
spencoid
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Re: refractometer accuracy and ???

Post by spencoid »

i did check the 0 with distilled water and it was right on 0 without having to adjust. the strange thing is what i mentioned that only the Mexican stuff differed greatly between hydro and refracto. since i am not using the refracto to measure Mexican alcohol, i guess i don't care.
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still_stirrin
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Re: refractometer accuracy and ???

Post by still_stirrin »

spencoid wrote:i did check the 0 with distilled water and it was right on 0 without having to adjust. the strange thing is what i mentioned that only the Mexican stuff differed greatly between hydro and refracto. since i am not using the refracto to measure Mexican alcohol, i guess i don't care.
Consider this: alcohol (& water) refractometers measure the refractive index of ethyl alcohol (& water) only. And those refractometers you find on Amazon measure up to 80%ABV, with appreciable error at either end of the scale (zero alcohol and 80%ABV alcohol. So, if you're trying to measure above 70-75%ABV, there will be error in the measurement.

Now, to answer the disparity between gins and other spirits when compared to the hydrometer measurements (not the label claims either), juniper oils, flavorings (artificial or organic), or sugars and even glycerin (for body and texture) will affect the light refraction index of the solution tested. Your Mexican spirit very well could have any number of additives which would negate a refractometer measurement.

In fact, additives with a density other than water will upset hydrometer measurements too. And since both ethyl alcohol have different thermal expansion coefficients, the calibration temperature of your Proof & Traille alcometer will be critical when taking density measurements. Temperature measurement and correction should always be done.

For the most accurate measurement that we hobbiests can make, the brewing refractometer will measure the original gravity (OG) and Brix (sugar content) in the wort/wash. You can also measure the OG with a brewer's hydrometer, as the fermentable (and non-fermentable) sugars add to the density of the solution.

But the final gravity (FG) is measured only with a brewer's hydrometer, and don't confuse that with the Proof & Traille alcometer used by distillers (see the hotlink in my signature). There are some who suggest that the brewing refractometer can be used to measure FG with adjustment calculations. But that is not really true...you may see remaining sugars in the refractometer, but the alcohol in the completed ferment will skew the readings.

When your distillate comes out of the product condenser, you can measure the %ABV or proof with the alcometer. Or, if it is within the calibratable range of the alcohol refractometer, you can measure it with that device. If you have one...use it. But recognize that it likely is not accurate at the extremes of its measurement scales.

A long oratory and I apologize. But I hope you understand better which tools are best for which process. As well as the limitations of those tools as well.

If you really do care about what you're measuring.....
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spencoid
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Re: refractometer accuracy and ???

Post by spencoid »

thanks for the explanations. i am interested in all this. nice to know about the high and low range inaccuracies of the refracto. the Mexican stuff is over the limit and probably all it took was a tiny amount of something with a highly different RI to throw it way off in the meter's most inaccurate range. i am only interested in using it for pure ethanol and probably more toward the middle range. i want to know when to stop the still. i know that the top vapor temp correlates well with percent alcohol. once i figure out my numbers (digital temp sensors are not absolutely precise but are very repeatable) i hope to be able to reproduce successful procedures.

if i do want to know the true strength of my alcohol distillations (before or after making it into gin) is the best method temperature corrected specific gravity measurement on an accurate scale? i have (if i can find them) some little volumetric flasks that have a narrow neck and a mark on them that is supposed to be something like 10 cc. if i can't find them i can get more as they are pretty standard glassware items. i have an old Metler analytical balance that i calibrated a long time ago but it is probably pretty accurate. i can weigh 10 cc of product to about .1 mg so i should be able to measure specific gravity pretty accurately. i have a Fluke digital thermometer that is supposed to be more accurate than my old mercury thermometers. I also have a NIST traceable temperature meter but have no idea when it was last checked.

i have the measuring gene i got from my father and grandfather. both engineers. Dad measured particle interactions (retired now after his last job on the super collider) , probably a little more difficult than what i need to do :)
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NZChris
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Re: refractometer accuracy and ???

Post by NZChris »

Unless you are commercial, accuracy isn't super important, especially for things like charging a gin still.

If you are commercial, or need to be very accurate for some other reason, get a certified alcometer from someone like Alla and keep it, and the liquor to be tested, in a controlled temperature environment. This can be as simple as putting a heating element in a small refrigerator and switching both heating and cooling with a cheap controller. If a cheap junk alcometer doesn't compensate correctly for temperature, as it should, keep that in the same cabinet and calibrate it, or spend more and get a real one.
cob
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Re: refractometer accuracy and ???

Post by cob »

spencoid wrote:what are og and fg?
really?
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