Reading / Calibrating a Hydrometer

[Dan]

Hi

Im trying to get to the bottom of why my actually OG figures are higher than the estimated from Beersmith. One of the areas Im looking at is my Hydrometer calibration.

The document that came with my hydrometer says it is calibrated to read correctly at 20deg C. Does this mean that, in pure water at 20 deg, it should read 1.000 or 0.998 (that actual SG of water at 20deg).

 My hydrometer reads 1.004 in pure water at 20 degs so depending on answer to above I reckon my hydrometer  readings are between 4 to 6 points too high, which goes a long way to explain my issue.

Any help appreciated..

Cheers

[Smiffy]

There are three probable causes of error.

1) the reading is normally taken at the surface of the liquid but some hydrometers are calibrated to be read off at the top of the meniscus to make reading "easier" with a coloured liquid.

2) the position of the numbers may be above the line rather than alongside them.

3) the temperature for which it is calibrated. Your figure of .998 for water at 20 deg C is only correct relative to the cold water at the standard 15 deg C. With your hydrometer, "calibrated to read correctly at 20 deg C" it should read 1.000 with plain water.

You can see from the attached pictures that the figures on mine are next to the line for .002 less, the line for the figure is below it. This is clear when you look at 1.020, but confused by the black bar at 1.006 - 1.010. In the other picture you can see that the liquid surface is 5 divisions above 1.010, i.e. 1.000, even though the 1.000 is completely hidden by the meniscus.

[Dan]

Thanks

My hydrometer is read from the top of the meniscus and this is where I read it from. Ive rechecked everything and it is definitely reading 4 points high at 20deg.

Short of buying another one, I guess I can just subtract 4 points from every reading to get something closer to the truth.

Cheers

[JackoNZ]

Hi Dan, I'm pretty sure it should read 1.000 at 20c. I just did some testing myself and mine is calibrated at 20c also and sits at 1.000. 

[Pilgrim]

As far as your Hydrometer is concerned then if you are reading it corrrectly, it sounds like you've got a crook one.

As for your OG being higher than estimated by BeerSmith, then remember that there are a lot of factors affecting the calculation, in particular your efficiency. Perhaps you are getting better mash efficiency than you are telling BeerSmith, this would leed to a low estimated OG.

[Dan]

Thanks

Ive been extract brewing/ steeping only to date so would have thought less factors at play is BSmith (provided the extract potential is roughly right (I use 1.036 for Blackrock light malt).

Im pretty sure my hydrometer is 4 points out.

Cheers