Hydrometer discrepancies

[Corbières]

Any guide me on this please ?
I’ve got two hydrometers - calibrated both today at 20c before checking FG on a stout.
One has a RED BAND
Calibration red band 1.004
Other spot on.
FG RED BAND 1.016/7
Other 1.008
So 4 points out at calibration and 8 or 9 on FG measure.

 

[foxbat]

That's strange isn't it? When the paper slips inside the glass tube you'd expect the error to be the same.

 

[Buffers brewery]

I guess it depends what you want to use the readings for. If you just want to check that fermentation is complete you can us either (but only one) to check that SG is steady. However, if you want to use the value to calculate with some accuracy the ABV, neither can be trusted and an investment in a “laboratory” standard hydrometer may be needed

 

[Buffers brewery]

You could try calibrating your hydrometers with different concentrations of sugar solution. This site has charts for brix v sugar solution and brix v sg.

https://too.uk.com/useful-information/

 

[Corbières]

I guess it depends what you want to use the readings for. If you just want to check that fermentation is complete you can us either (but only one) to check that SG is steady. However, if you want to use the value to calculate with some accuracy the ABV, neither can be trusted and an investment in a “laboratory” standard hydrometer may be needed

I would like to know ABV more accurately- any recommendations for a “lab” hydrometer ?

 

[Buffers brewery]

Sorry, I don't have any experience of this type of instrument but Google identified this supplier.

https://www.coleparmer.co.uk/c/hydrometers
I calibrated my cheap hydrometer using different concentrations of sugar solution as I suggested above and produced a graph. As it happened my hydrometer wasn't far out but it sounds like one of yours is a rogue

 

[Corbières]

Sorry, I don't have any experience of this type of instrument but Google identified this supplier.

https://www.coleparmer.co.uk/c/hydrometers
I calibrated my cheap hydrometer using different concentrations of sugar solution as I suggested above and produced a graph. As it happened my hydrometer wasn't far out but it sounds like one of yours is a rogue

 

[Corbières]

Thanks - pricey
I’ll try your recommended sugar solution calibration and take it from there.

 

[Buffers brewery]

It worked for me

 

[The Baron]

As Buffers says most cheapo/wilko hydrometers are good enough for homebrewing you only need to spend on the expensive ones if you want a exact reading to .2 i.e you are a little anal which some brewers are or you are running a brewery.
Just calibrate it and if its off just adjust any reading it will be near enough for most homebrewers

 

[Corbières]

As Buffers says most cheapo/wilko hydrometers are good enough for homebrewing you only need to spend on the expensive ones if you want a exact reading to .2 i.e you are a little anal which some brewers are or you are running a brewery.
Just calibrate it and if its off just adjust any reading it will be near enough for most homebrewers

Agreed. Having two so far apart has been the issue. I’ll calibrate one and go fro there.

 

[foxbat]

I would like to know ABV more accurately- any recommendations for a “lab” hydrometer ?

A Stevenson Reeves saccharometer, are I believe HMRC approved if you really must have that level of accuracy.

 

[Hop_it]

The suggestions to calibrate against known sugar solutions are sound, but it is also worth remembering to adjust for the 'offset', i.e. the error in the reading you get with just plain water (at the prescribed temperature). I use 2 hydrometers - one wide range for OG, and one narrow range for a more accurate FG reading. In both cases the reading for pure water is offset below 1.000 by 0.1 and 0.2 respectively. I have confidence in the overall accuracy of the printed scales of both hydrometers, so I just add the offset to any reading that I take. . . . . . . . However, in your case I do accept that you are getting such radically different FG readings that at least one of them must be wrong.

 

[Pavros]

Are both hydrometers supposed to read 1.000 at 20C? Some read 1.000 at 18C - it should tell you which temperature to use in the instructions or on the packaging somewhere.

Although that doesn't explain the difference in FG reading which I would expect to be consistent unless there was another temperature difference between the samples.

 

[Corbières]

Are both hydrometers supposed to read 1.000 at 20C? Some read 1.000 at 18C - it should tell you which temperature to use in the instructions or on the packaging somewhere.

Although that doesn't explain the difference in FG reading which I would expect to be consistent unless there was another temperature difference between the samples.

Both 20c
FG photos were taken with 2 mins of each other so temperature was the same.

 

[Pavros]

Yeah, it would have to be a fairly large temperature difference to account for an extra 4 points between the readings

 

[nickjdavis]

When "calibrating" in water, if you get a reading that is higher than 1.000 simply make the hydrometer a bit heavier by cutting a small length of electrical tape and sticking it round the tip of the hydrometer....doesnt take much...maybe a centimeter or so, to adjust downwards by two or three gravity points.....its easy to fine tune as you just need a pair of scissors to cut off any excess tape.

However, I've not yet found a method of adjusting a hydrometer that under reads!!!

 

[Hop_it]

When "calibrating" in water, if you get a reading that is higher than 1.000 simply make the hydrometer a bit heavier by cutting a small length of electrical tape and sticking it round the tip of the hydrometer....doesnt take much...maybe a centimeter or so, to adjust downwards by two or three gravity points.....its easy to fine tune as you just need a pair of scissors to cut off any excess tape.

However, I've not yet found a method of adjusting a hydrometer that under reads!!!

The scale on a typical inexpensive brewers hydrometer is linear, so all you need to know is the positive or negative offset from 1.000. Any error is most likely caused by the scale having been stuck in the wrong position before being sealed into the tube above the weighted bulb. If the graduations were really incorrectly spaced then its only fit for the bin, and (in my own very humble opinion) it's not worth trying to recalibrate it.

 

[Corbières]

You could try calibrating your hydrometers with different concentrations of sugar solution. This site has charts for brix v sugar solution and brix v sg.

https://too.uk.com/useful-information/

Today I made up a sugar solution of 75g in 1L of water. Both hydrometers have a scale to measure amount of sugar per L
It is clear which hydrometer is out. Thanks for all of your responses.

 

[nickjdavis]

The scale on a typical inexpensive brewers hydrometer is linear, so all you need to know is the positive or negative offset from 1.000. Any error is most likely caused by the scale having been stuck in the wrong position before being sealed into the tube above the weighted bulb. If the graduations were really incorrectly spaced then its only fit for the bin, and (in my own very humble opinion) it's not worth trying to recalibrate it.

I dont disagree and that's all well and dandy if you only have one hydrometer and only one offset to remember. I brew in a garage with a concrete floor. Glass hydrometers, gravity and concrete isnt a successful mix of ingredients....hence I have at least two hydrometers available for use at any time....picking up a random hydrometer out of two (or sometimes more) examples I wouldn't know which one I'd got and which offset, if any, to apply....hence the calibration.

Funnily enough, despite my comment about making a hydrometer lighter...I've never actually had one that under-read!!!