What could cause a Hydrometer to start giving incorrect readings?

[Markus]

So last night I checked on my batch of bitter, which has been neglected for the holidays. The hydrometer read 1.000 exactly. Once I'd gotten over the initial reaction of "Wow, cool!" and realised that this was very unlikely I decided I should probably test the Hydrometer. So I tested it with water and the reading was an equally improbable 0.992...

So essentially the hydrometer is off by .008.

This is a hydrometer I've been using for years by the way, and it has worked perfectly up until now. The last 3 recent batches I did all came out perfect so I don't think the readings were off then.

The only thing I can think of is that I recently left the hydrometer in the brew area for a week or so at 20 degrees. Would this throw the reading off? Only other thing, and this just occurred to me, is it possible that the label inside the hydrometer just shifted a bit?

 

[LloydV]

I have had the paper slip slightly on an old hydrometer ( while shaking it to try and get it back I dropped it).

 

[Chippy_Tea]

Why do you need to calibrate the hydrometer?

There are many sources of errors when you use a hydrometer, either it is a cheap one or an expensive lab quality one.

Temperature: The same liquid will show different readings at different temperatures. High temperature means lower reading. Your hydrometer usually states what temperature to use it at (normally 15-20 C). If you have a liquid with another temperature there are formulas to calculate the correct value. But then of course you need an accurate thermometer as well.

Scale movement: The scale inside your hydrometer is usually glued inside to the glass and quite often the glue is not good enough which means it slides up or down.

Scale misplacement: In production, especially on cheap hydrometers, the scale might have been fitted in the wrong position. A more expensive hydrometer would probably have been tested in water before approval so you are less likely to have this problem the more money you spend on your hydrometer.

Scale distortion: Scales are often photocopied from previous production run and eventually this might distort the scale. This is a less common problem and if it is there, it us usually very small, which is fortunate because we can not calibrate this error away (since it is non-linear).

 

[Fil]

cleaning/sanitising at too high a temperature can melt the glue holding the scale in place, i did that and didnt notice till the end of the following brew!!:wha:

 

[matt76]

cleaning/sanitising at too high a temperature can melt the glue holding the scale in place, i did that and didnt notice till the end of the following brew!!:wha:

Think i might have answered my own question here...

Bit of a thread resurrection but always fun to use the search function

Now i think about it i haven't always cooled my gravity samples and in one case it was hot enough to warp the trial jar - oops

I remember testing my hydrometer when new and it read 1.000 in water at 20degC - more recently i noticed it was 1.002 and yesterday i checked and it gave me 1.004 from mains water and 1.003 from softened water.

This would explain my recent FG's being a few points higher than I might expect, despite the beer appearing in every other respect to be "done". Since ABV is determined from the difference between OG and FG I guess it's not a major issue (not that ABV is the be all and end all anyway), though when it comes to tweaking figures in Brewer's Friend it means my yeast probably is attenuating a few percent more than I thought.

 

[Benfleet Brewery]

I had a problem with mine and found it was because it was sticking to the side of the plastic trial jar. Not had the same problem since I started using a glass jar.