Do Hydrometers lose accuracy?

[Opdog]

I have two proof and tralle alcoholmeters that I bought from Brewhaus. I bought one years ago when I first got started and another one I bought recently when I broke my hygrometer and thought I should probably have an extra on hand just in case.

I’m about to proof down some high test to put in a barrel and was double checking the ABV that I wrote on the bottle to make sure that the dilution was correct. I used the old alcoholmeter and the numbers were consistently 5% lower on an uncorrected basis. I thought that maybe the temp was significantly different. I’m doing the measurement at my basement bar, which stays at a pretty consistent 68F. I grabbed the new meter and it measured dead on the number I wrote on the bottles. So one of them is off.

I took a gallon of distilled water that I’m using to dilute my spirit and both meters measure accurate at zero. How do I figure out which one is off? It is only about 5% but I’d still like to have confidence that my measurements are accurate.

I don’t have any store bought vodka on hand to do a reference check there at the moment.

Any thoughts or advice is welcome.

[GNBrews]

What *may* have happened is that the paper inside with the printed graduations has broken free and slipped. It doesn't usually happen though unless you've given it a good bump.

Note that alcometers are usually calibrated at 60F and you'll need to adjust for that higher temperature. That wouldn't account for a full 5% though.

[stillanoob]

If the paper hasn't moved then most likely one was off to start with. Get some store bought and find out.

[IDPotatohead]

I just noticed the same issue with mine from Brewhaus that's several years old. That was weird to see this post....

[The Baker]

"...I have two proof and tralle alcoholmeters that I bought from Brewhaus. I bought one years ago when I first got started and another one I bought recently when I broke my hygrometer..."

Auto-correct strikes again?
A hygrometer measures humidity.

A hydrometer can be calibrated to measure alcohol content.

Geoff

[NZChris]

A man with one watch always knows what the time is.
A man with two watches is never quite sure.

For decades, I had no complaints about my original alcometer and was happy with the results, then I started checking the results of proofing and discovered the numbers didn't add up and the proof was never what was calculated. I bought a certified 70-100% Alla and discovered that the paper scale in my old faithful was 3mm out. I have no idea how accurate it was when I bought it.

Now that I have a more accurate alcometer to calibrate other alcometers against, am I happier, is my booze better? Probably not.

[Cristof]

I have 7 different alcoholmeters and I think everyone shows a little different value. That's what you get with 5-10€ stuff. Once I wanted to buy certified alcoholmeter (it's scale is only 5% and is very precise and have thermometer) but when I knew the price I changed my mind. It cost around 80€.

[Chauncey]

Check your thermo, make sure your liquid temp is actually correct for your calibration temp. make sure the paper aint slipped, etc etc. I have a carlson that seems to be pretty legit. Had it for a hot minute. Knock on wood.

[Yummyrum]

Im guessing paper hasn’t moved otherwise both wouldn’t be reading 0ABV in distilled water .

Check the calibrated temp for both . Most are 20°C ... but not all .
Sample temp makes a big difference . Also be aware when you temper spirit that it will heat up when you add water . So if you take a reading , add calculated amount of water , unless you retake temp reading , the new Tempered ABV will read a lot higher .

[Demy]

I would say it is a nice dilemma, despite many hypotheses I think it is difficult to find the problem. If it was a paper problem you would find the same error with water, if it was the temperature and you measure the same distillate at the same time you would still find the same problem. I think there is a problem with the construction (for example the calibration sinkers on the bottom) but honestly I don't know if this would give a different reading with alcohol and 0 with water. If I were I, I would try to measure neutral alcohol using a third instrument as a comparison (even if this does not give the certainty that the third is accurate).

[Chauncey]

I may be wrong but arent some alcohometers and hydrometers made to use a specific sized cylinder?

[bluefish_dist]

The cheap ones don’t have all that good accuracy. The expensive ones $35-$40 per, have been no more than .1 proof off when I had them calibrated. The cheap full scale ones I have were off by 3-5 proof.

[hefezelle]

Perhaps there's some smudge sticking to the outside, altering your measurements? Use some window cleaner to gently clean the glass, then rinse well with water and finally distilled/de-ionized water. Use rubber gloves while doing this (and during any subsequent handling of the hydrometer) and be careful not to drop it.

Also make sure there are no droplets sticking to the part of the hydrometer that's above the liquid surface before reading it off! Same goes for bubbles forming on the immersed part of the hydrometer.

[shadylane]

My theory is.
You haven't been leaving enough alcohol for the leprechauns that live in your basement.
The little buggers can cause all sorts of mayhem when they started getting bored or thirsty.

[Cristof]

I may be wrong but arent some alcohometers and hydrometers made to use a specific sized cylinder?

The amount of liquid doesn't matter, because they work on the principle of buoyancy, and that is same in 100ml or 100l.

[stillanoob]

I may be wrong but arent some alcohometers and hydrometers made to use a specific sized cylinder?

The amount of liquid doesn't matter, because they work on the principle of buoyancy, and that is same in 100ml or 100l.

Surface tension can come into play. So too narrow can throw results off.

[Birrofilo]

I would buy a bottle of 95% alcohol at a store. That should be presumably very near the stated value, and the deviation should be much less than 5%.

I would then do the following test. Get a graduated container and a receiving container. Use always the same "mark" of that container. For instance, the 100 ml mark. Let the liquids and the containers sit at 20°C for a couple hours.

Prepare some quantity with 4x alcohol and 1x distilled water (e.g., 400 ml alcohol and 100 ml distilled water). You should always use the same mark, so e.g. in order to make a 4x and 1x mixture, fill the graduated container 4 times with alcohol up to the mark, and pour the alcohol in the receiving container, then fill the graduated container with distilled water up to the mark, and put the water into the receiving container.

Now dip both alcoholmeters and take the readings for each measurement in a four-column sheet. E.g.
Parts alcohol; Parts distilled water; Theoretical ABV; Reading instrument A; Reading instrument B;

Now add a measure of distilled water into the receiving container and repeat the two measures.

You should collect data for (parts alcohol and parts water);
4x and 0x;
4x and 1x;
4x and 2x;
4x and 3x;
4x and 4x; (that's 47,5% ABV if your product was 95%);
4x and 5x;
4x and 6x;
4x and 7x;
4x and 8x; (that's around 31,5%);
...

You should easily see which of the two instruments is off-mark at 20°C.
They will tend to converge at 0% volume (water) and presumably show an increasing divergence with the increase of the alcohol content.

You could also use a refractometer to see which of the two alcoholmeters is way off.

[Yummyrum]

Thats a good test Birrofilo .

Methylated spirits we buy here is pretty much a standard 95.0% avb and a good reference for calibrating high end of an Alcometer

[Birrofilo]

If you have a precise refractometer which you trust, and well calibrated, you could use it to spot which of the two alcoholmeters is off.

You can do this by using these two sources:
Janina Nowakowska: The Refractive Indices of Ethyl Alcohol and Water Mixtures, 1939
United States Department of Agriculture: sucrose conversion table, FILE CODE 135-A-50 JANUARY 1981

You need the second document only if, as usual, you have a refractometer which is graduated in Brix degrees (water-suger mixture). But you might have a refractomter which gives you the refraction index and you would use the first source only, and you could have a refractometer which is graduated for alcohol content, and then you need no sources at all

Let's say you have a refractometer which measures the sugar content of a sugar-water mixture in Brix degrees.
You put your Water-alcohol mixture in it and the instrument tells you 16,7 °Brix.
Your instrument tells you that your sugar-water mixture is 16,7 Brix but it doesn't know that your mixture is alcohol-water (or whatever else). All that the instrument knows "internally" is that the mixture has a refractive index of 1,3584. Instead of showing you "RI = 1,3584" which is of no use to you, the instrument applies the conversion (which is in a table in the second source) and tells you directly "16,7 degrees Brix".

What you are interested in is that that your alcohol-water mixture has the same refractive index than a sugar-water mixture of 16,7 degress Brix, and that is 1,3584.

Now you get the first document, and see which water-alcohol mixture you have given that refractive index. You see from Table II that you are very near 41,51% by weight (you now have to convert into alcohol "by volume" using some calculator).

Basically you can prepare a mixture which is more or less 45% (one part your store-bought 95% bottle and one part distilled water), you measure it with your refractometer, which probably gives you a "Brix" value, you find in the second document the corresponding refractive index, and you find in the first document the alcohol-content by weight for that refractive index, and you convert it into ABV. The alcoholmeter which gives you the closest number to that is the more precise.

Note that the RI reaches its maximum at 82,86 ABW then decreases again, so you have to know in which "region" of alcohol content you are to translate a RI into an alcohol content.

[Birrofilo]

@yummyrum

I was thinking at the 95% alcohol than one can buy for actual liqueur preparation, in food stores (that's usually called "alcohol buongusto" here, "goodtaste alcohol"). One pays the excise tax (the horror of it!) but nothing is wasted: after the tests, one can put it at good use But thinking about it, I think one can find 95° rubbing alcohol here (the pink stuff) although normally it is 90° and, in that case, I don't know how "precise" is that number (it could be 92° or 88° and probably be within commercial specifications). The 95% kind should be "precise" in alcohol content, one would presume, being taken from the azeotropic production without dilution.

[NZChris]

But thinking about it, I think one can find 95° rubbing alcohol here...

It has a different Specific Gravity to ethanol, so it won't work.

[Birrofilo]

But thinking about it, I think one can find 95° rubbing alcohol here...

It has a different Specific Gravity to ethanol, so it won't work.

I don't know what you exactly mean for "rubbing alcohol" in the US or elsewhere. What we find here in Italy is "alcol etilico denaturato". It's ethylic alcohol so it should have the same specific gravity, ot maybe you mean that the denaturant alters the specific gravity enough to render it useless for the purpose of this thread?

I understand in other countries is easier to find methylic alcohol. I have never seen methylic alcohol in general stores in Italy, although it is certainly available in specific stores (for what I remember it was a favourite for scale models' engines). For what I know, methylic alcol is forbidden also as a denaturant here.

[Yummyrum]

Downunder , we consider Rubbing Alcohol to be Isopropyl ( or Isopropanol.... or Propan-2-ol) ... not Ethanol .

[higgins]

In the US rubbing alcohol is 70% isopropyl alcohol, and an ABV refractometer reads zero.