Questioning hydrometer accuracy

[Antzrhere]

Hi All.

Although I have been brewing for a few years now this is my first post, so hello!

I was brewing an all-grain IPA a few weeks ago and as you do, I took a gravity reading of the sparged wort. For some reason I have two typical glass hydrometers lying about(useful if you frequently smash them while sanitising!) , a rather plain cheap looking one with no calibration info and a more 'expensive' looking one with more markings, colours and some calibration info saying "made I France". I can't remember where I got either of them from but I've spotted the latter in one of my local homebrew shops here in the North West of England.

Anyway out of interest I took readings with both of these hydrometers and to my surprise the cheaper looking one read 1.030 and the other one read 1.040. My final gravity reading of the wort read 1.070 with one and 1.085 with the other.

The next day I decided to make up some known sugar solutions at different concentrations to determine which hydrometer was accurate using a beer tool online. Low and behold the cheaper hydrometer was correct within +/- 0.001 points at both 1.030 and 1.070.

I also decided to see what they read in pure water (unfortunately not distilled, but as you will see this wouldn't have made a difference) - both read 1.000 spot on.

Further to this there was no visible damage (i.e. chips) to either hydrometers that might make the gravity reading incorrect.

As the error rate of the higher reading hydrometer is not linear, ranging from correct in pure water to +0.010 at low sugar concentrations up to +1.015 at a prospective 8% ABV beers this would indicate it's not just a case of the paper markings slipping, but rather a manufacturing defect.

I know many people test their hydrometer by zeroing in pure water, but as is the case here that wouldn't have detected the problem. My question is how many of you have tested with known liquid densities (i.e. sugar solutions)?

My thoughts were that the implications of this would be more than just incorrectly calculating ABV (which matters little to a home brewer if truth be told other than bragging rights) but that your calculated mash and brew house efficiencies would be way off, approximately +14% in this case which is a big deal.

 

[ncbrewer]

I agree, that's a big deal. And it's really worrisome since the normal one or two point calibration wouldn't have caught it. Temperature correction would be iffy for the one with no calibration info - did you assume 60F calibration temp? That could be part of the problem.

 

[55x11]

Hi All.

Although I have been brewing for a few years now this is my first post, so hello!

I was brewing an all-grain IPA a few weeks ago and as you do, I took a gravity reading of the sparged wort. For some reason I have two typical glass hydrometers lying about(useful if you frequently smash them while sanitising!) , a rather plain cheap looking one with no calibration info and a more 'expensive' looking one with more markings, colours and some calibration info saying "made I France". I can't remember where I got either of them from but I've spotted the latter in one of my local homebrew shops here in the North West of England.

Anyway out of interest I took readings with both of these hydrometers and to my surprise the cheaper looking one read 1.030 and the other one read 1.040. My final gravity reading of the wort read 1.070 with one and 1.085 with the other.

The next day I decided to make up some known sugar solutions at different concentrations to determine which hydrometer was accurate using a beer tool online. Low and behold the cheaper hydrometer was correct within +/- 0.001 points at both 1.030 and 1.070.

I also decided to see what they read in pure water (unfortunately not distilled, but as you will see this wouldn't have made a difference) - both read 1.000 spot on.

Further to this there was no visible damage (i.e. chips) to either hydrometers that might make the gravity reading incorrect.

As the error rate of the higher reading hydrometer is not linear, ranging from correct in pure water to +0.010 at low sugar concentrations up to +1.015 at a prospective 8% ABV beers this would indicate it's not just a case of the paper markings slipping, but rather a manufacturing defect.

I know many people test their hydrometer by zeroing in pure water, but as is the case here that wouldn't have detected the problem. My question is how many of you have tested with known liquid densities (i.e. sugar solutions)?

My thoughts were that the implications of this would be more than just incorrectly calculating ABV (which matters little to a home brewer if truth be told other than bragging rights) but that your calculated mash and brew house efficiencies would be way off, approximately +14% in this case which is a big deal.

Very interesting. I have 3 hydrometers and a few refractometers and usually hydrometers are within 2 points or so (adjusting for zeros that may be off) - I will check again with sugar solutions. Interesting test.

1.085 vs. 1.070 means that it's not uniform (or not calibrated) cross-section at the narrow part to more than 20% or so. That's a huge tolerance violation.

 

[Antzrhere]

Yes both were measured at 18C. Either way a few degrees temperature wouldnt cause that much error. Five degrees C typically adds/looses a point (0.001)

I might purchase another of the same brand and see if it reads the same. Ill take pics of the suspect hydrometer tomorrow.

Probably wont affect most people out there but who knows, thought it was interesting enough to share

 

[Antzrhere]

Sorry to resurrect an old thread, but I've just found out the inaccurate hydrometer in question was purchased from Wilkonson's (or Wilko) here in the UK - my friend purchased one (the same as mine) and it's reading the same error (too high).

 

[Ulf Kavlie]

If you thought you were resurrecting an old thread, then hold my beer.

Firstly, this is my first post here, so hello to everyone. Secondly, I am based in Europe, so all the values will be given in the metric system, I apologize in advance to all the Americans here.

Yesterday I was going to calibrate my new RAPT Pill. Now, I am a huge math/statistics nerd, so of course I went for the custom calibration, where you calibrate the Pill in different solutions.

I did the calculations and found that I needed 208.3 grams of sugar, dissolved in 1l of water, to get an SG of 1.08, and calculated what amount of water I needed to dilute it down to 1.01, with .01 increments (please see table1 and calculations below). The solution was blended, not boiled, to avoid water loss due to vaporization so that it would stay as accurate as possible. Furthermore, I weighted my water with 0.1g accuracy, for the same reason as stated above. The temperature of the water was 20C (68F).

I felt I was very precise in my process, so it was a shock to me when I did my gravity reading with a hydrometer, and it showed 1.068!

I checked all my calculations and did a new blend of water and sugar, and the same result. Now, my hydrometer has always been a little off (±0.002 in tap water, excellent tap water, so no need for distilled water IMO), but nothing like this.

I decided to go on with the calculations instead of the hydrometer but checked the hydrometer reading for each step, and the error decreased for each dilution until it reached the normal error of ± 0.002 at tap water.

My question to you, is if any of you have had the same trouble, or have any idea of what is happening to my hydrometer? As stated above, the hydrometer seems reliable in normal water, but the error increases as the gravity does, and doesn’t even give a reliable reading at 1.04. I worry that my RAPT Pill is incorrectly calibrated when values are based on pure theory.

Dilution of syrup table

SG​	Sugar​	Milliliter​	Accumulative addition​
1,08​	208,3​	1000,0​	1000​
1,07​	208,3​	1142,9​	142,9​
1,06​	208,3​	1333,3​	190,5​
1,05​	208,3​	1600,0​	266,7​
1,04​	208,3​	2000,0​	400,0​
1,03​	208,3​	2666,7​	666,7​
1,02​	208,3​	4000,0​	1333,3​
1,01​	208,3​	8000,0​	4000,0​

Formulas used
Sugar needed = (( Theoretical Gravity - 1 ) * 1000 * Liter / 384 ) * 1000


Dilution = ( Sugar Content * 384 ) / ( Theoretical Gravity - 1 ) * 1000

 

[huckdavidson]

Have you ever calibrated your hydrometer with a sugar solution or only at 0.000 with tap or distilled water?

It wouldn't be the first time a printed hydrometer scale was off. Is this a higher end hydrometer?

How are you mixing your sugar solution? Adding 208.3 grams of sugar to 1 liter of water -or- adding 208.3 grams of sugar to half liter of water, dissolving, then topping up to 1 liter?

If the pill read the theoretical values and you're sure of your weight and volume measurements, it should be able to be trusted.