How to calibrate your hydrometer

[Kegory]

I found this great article which explains how to calibrate your hydrometer.

https://beerandbrewing.com/calibrating-your-hydrometer/

I'll be calibrating mine soon and I'll post the results here. 

[Classic Brewing Co]

30 minutes ago, Kegory said:

I found this great article which explains how to calibrate your hydrometer.

https://beerandbrewing.com/calibrating-your-hydrometer/

I'll be calibrating mine soon and I'll post the results here. 

I reckon I have posted that & others a hundred times over the years. 

[Kegory]

I'm sure you have, Phil. I even think I found the link to this one at the bottom of another article you posted a link for.

I just thought it would be good to make a thread about. I think it may be interesting for other new brewers. The accuracy of hydrometer readings was recently brought up in another thread.

[Classic Brewing Co]

41 minutes ago, Kegory said:

I'm sure you have, Phil. I even think I found the link to this one at the bottom of another article you posted a link for.

I just thought it would be good to make a thread about. I think it may be interesting for other new brewers. The accuracy of hydrometer readings was recently brought up in another thread.

Yes, it is important to know how to read them properly otherwise you may as well not use it. I have seen people record the wrong readings in the past.

[Otto Von Blotto]

I remember reading somewhere that distilled water is actually 1.000 at 4°C, not 20. I looked into it when I was getting a bit confused as to whether my own hydrometer was measuring properly or not because it always reads 0.998 in 20°C water, and I thought it was off. Turned out it's exactly what it should be. I did measure the water at 4 degrees as well and it read 1.000.

As a result of that when I take readings I temperature adjust for 4 degrees rather than 20. 

[Kegory]

1 hour ago, Otto Von Blotto said:

I remember reading somewhere that distilled water is actually 1.000 at 4°C, not 20. I looked into it when I was getting a bit confused as to whether my own hydrometer was measuring properly or not because it always reads 0.998 in 20°C water, and I thought it was off. Turned out it's exactly what it should be. I did measure the water at 4 degrees as well and it read 1.000.

As a result of that when I take readings I temperature adjust for 4 degrees rather than 20. 

Thanks Otto, I think you just broke my head on this sunny Sunday morning.

I found this article which has charts and tables for Water - Specific Gravity vs Temperature.

Now I desparately need another coffee.

[Kegory]

Hydrometer Calibration Day

First I tried the 4C measurement using my known to be not entirely trustworthy thermometer (read 0.4C in freezing water & 101.5C in boiling water).

The Coopers hydrometer reads about 0.094

The glass hydrometer reads about 1.005

The glass hydrometer came with a corrections table.

And, of course, putting a couple of hydrometers at an ambient temperature of around 12C into a flask of 4C water raised the temperature of the water.

Conclusion: neither of my hydrometers are accurate in the 4C - 6C range.

[Kegory]

Next I took readings at approximately 20C.

The Coopers hydrometer didn't register much of a change giving a reading of about 0.096.

The glass hydrometer didn't change much, either, or perhaps at all, giving a reading of 1.003 - 1.004.

I got a little bit clever before taking the readings, using the cooler hydrometers to bring the water temperature down and simultaneously using the warmer water to raise the hydrometer temperatures. A post reading temperature check registered only a small change.

[Back Brewing]

Very in depth experiment I think I will just keep plodding along with my readings 

[Kegory]

44 minutes ago, Back Brewing said:

Very in depth experiment I think I will just keep plodding along with my readings 

Sure, but I'm trying to avoid, or at least delay, mowing the backyard.

[Kegory]

Now for the second calibration point, according to the article, or, in this case, third.

The article says dissolving 15g of table sugar in 89ml of water results in a solution of 15 degrees Plato which reads as a Specific Gravity of 1.061. It then says to make a solution of enough volume to float the hydrometer to dissolve 30g of sugar in 170ml of water.

That doesn't add up. I think the amount of water is a typo in the second volume so I made a solution of 30g of sugar in 178ml of water.

I heated it in the microwave, stirred, and cooled it down in the fridge, then sat the hydrometers in it to balance the temperature before eventually taking a reading.

The Coopers hydrometer gives a reading of around 1.055.

The glass hydrometer gives a reading of about 1.064.

And I forgot to immediately take a temperature reading but took this one a couple of minutes later.

 

[Kegory]

Conclusions:

The Coopers hydrometer is reading 0.004 - 0.006 below the expected readings at temperatures of around 5C and 20C. I'll give that a Rule of Thumb @ -0.005.

The glass hydrometer is reading 0.003 - 0.005 above the expected readings at temperatures of around 5C and 20C, without allowing for the corrections table. I'll give that one a Rule of Thumb @ +0.004.

Remaining mysteries:

I once got the same readings from both hydrometers and another time there was only 0.001 difference between them. How to explain that?

[Otto Von Blotto]

They should be floating freely in the water rather than leaning against the side of the tube, but otherwise the only thing that explains why they're reading different and the same at different times to me is they're probably at the lower end of the quality spectrum. 

Mine isn't high end either but it reads consistently. 

[Kegory]

11 hours ago, Otto Von Blotto said:

They should be floating freely in the water rather than leaning against the side of the tube, but otherwise the only thing that explains why they're reading different and the same at different times to me is they're probably at the lower end of the quality spectrum. 

Mine isn't high end either but it reads consistently. 

Maybe it's something to do with barometric pressure and the phase of the moon.

[Tricky Micky]

21 hours ago, Kegory said:

22 hours ago, Back Brewing said:

Very in depth experiment I think I will just keep plodding along with my readings 

Sure, but I'm trying to avoid, or at least delay, mowing the backyard.

Extremely in depth experiment. But I think you may now have a bigger problem in the backyard.

[Kegory]

1 hour ago, Tricky Micky said:

Extremely in depth experiment. But I think you may now have a bigger problem in the backyard.

Astute observation, Micky. However, unlike the backyard, I only have to calibrate the hydrometers once.

[Classic Brewing Co]

29 minutes ago, Kegory said:

Astute observation, Micky. However, unlike the backyard, I only have to calibrate the hydrometers once.

 I would wear combat gear; you may encounter trouble in there!

[Coopers DIY Beer Team]

On 8/27/2023 at 10:37 AM, Kegory said:

The Coopers hydrometer didn't register much of a change giving a reading of about 0.096.

The Coopers Hydro's are calibrated to read 0.998 in distilled water @ 20C so yours looks to be out by about 2 points. Although the SG scale is not strictly linear, it's close enough for most DIY applications, so adjusting your readings by two points will give you a reasonably accurate figure. 

Cheers, Frank.

[Kegory]

27 minutes ago, Coopers DIY Beer Team said:

The Coopers Hydro's are calibrated to read 0.998 in distilled water @ 20C so yours looks to be out by about 2 points. Although the SG scale is not strictly linear, it's close enough for most DIY applications, so adjusting your readings by two points will give you a reasonably accurate figure. 

Cheers, Frank.

Thanks Frank

[Kegory]

Cheers Frank @Coopers DIY Beer Team