....but no-one seems to have asked this before......

do hydrometers 'age'? Can a hydrometer become unreliable simply
because it is old?

I have some, to say the least, "suspicious" readigs on mine lately,
despite normal technique(normal "by the book", not normal for me
before you ask) .

I'm not reading at high or low temps, I havent exposed the instrument
to extremes, it is not cracked... and neither am I, beyond the degree
common to most country winemakers

Sean

Sure, maybe in 500 to 1000 years... No, they don't age.
Hydrometers can be damaged though. I am a metrologist, I used to
calibrate things.

The little paper scale slipped into the stem can come loose; if it
does (and that is exceedingly rare) you will develop an offset. If
you take a very finely graduated scale and place it next to the scale
on any hydrometer you will notice the scale is not linear, it's close
but not exact, so if the scale moved it's not a good thing.

So here is how you check it. Look at the scales, somewhere on it it
will tell you the calibration temperature. That is the temperature at
which the scale is precise and can be read directly. If you can't
find a temperature noted it's probably not very good to begin with but
assume its 68F (20C). Get some distilled water at the calibration
temp, stir it to make sure the temperature is equal and place the
hydrometer in, spinning it as you lower it (like a top). It should
read 1.0000 at the calibration temp; any deviation is considered an
offset that has to be accounted for on all readings. An offset of
0.002 or less is not a big deal, just note it.

Cleaning can also affect it, the skin of the device needs to be very
clean. I use Alconox to clean everything but that is not necessary,
just use any good detergent you use now and dry it, you don't want
water spots. If you want something perfectly clean you follow that
with a rub down of grain alcohol, that leaves no residue. (It will
look like you just wasted grain alcohol but believe me, it's clean now
if it wasn't before.)

Temperature corrections are needed because water density changes with
temperature and that is not linear either.

To calibrate a hydrometer used for fermentation pure sucrose is used.
Table sugar is better than 99.5% pure so it's good enough. I have the
tables for that and can email you them if you want to do that. In
summary, temperature correction, cleaning and a check of zero are all
that is needed for the most part.


Joe

On Mar 25, 9:29 pm, "snpm" wrote:
...but no-one seems to have asked this before......

do hydrometers 'age'? Can a hydrometer become unreliable simply
because it is old?

I have some, to say the least, "suspicious" readigs on mine lately,
despite normal technique(normal "by the book", not normal for me
before you ask) .

I'm not reading at high or low temps, I havent exposed the instrument
to extremes, it is not cracked... and neither am I, beyond the degree
common to most country winemakers

Sean

I have one that i bought at an auction maybe 5years ago and was stored
poorly(freezing temps, direct sunlight, etc) and I did half the test
joe mentioned. read 1.000 on the dot.

joe if the tables are not too large, i'd suggest putting up here.
sound like a wonderful way to test a questionable hydro.

or buy a second and use both every time you test. if good they should
both match