Hydrometer

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Hydrometer

Postby Danespirit » Sun Aug 16, 2015 9:58 am

A hydrometer used in homebrew and wine making, needs either very precise factory calibration (that will cost you $$) or you need to calibrate it every time you use it. Fortunately, this is very simple so you can turn your standard homebrew hydrometer into a precision instrument with minimum effort.
You can easily calibrate for most errors and use a low cost hydrometer to get a high quality reading using the following procedure:

Keep a testjar/graduated cylinder with water near your brew. The idea is that this water have the same temperature as your brew so leave it there all the time.
Like when making your ferment it is essential that you work clean, so always use a clean testjar/graduated cylinder and fresh water.

Before using your hydrometer (always!): Check the reading of the water. It should be around 1000 s.g. (0 on hydrometers showing oechsle degrees) but it will vary depending on temperature and scale errors.

If your hydrometer shows, say 1002 (+2) you obviously need to take your reading minus 2 to get it right. Then simply take all your ferment readings minus 2 and that's it!

If your hydrometer shows 0.998 (-2) on the water - just add 2 to all your readings.

Remember that you have to check the water reading every time because temperature might have changed and/or your hydrometer scale might have moved inside the hydrometer. The beauty with this procedure is that it compensates for both temperature and scale moving errors at the same time so no need any more to make sure that the beer/ferment has a certain temperature before measuring the specific gravity.

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. You can also find a datasheet online, regarding the different readings respective to temperatures.

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 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.

NOTE: A hydrometer or oechslemeter measures only the s.g. (sugar) , it CAN'T be used to measure the alcoholcontent (ABV).

To read about how to use a hydrometer, please see Bushmans excellent post here: http://www.homedistiller.org/forum/view ... 61&t=42746

hydrometer with thermometer.gif
Hydrometer with inbuild thermometer
hydrometer with thermometer.gif (4.58 KiB) Viewed 1587 times
GPSD.gif
GPSD.gif (63.83 KiB) Viewed 1587 times
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Re: Hydrometer

Postby still_stirrin » Sun Aug 16, 2015 3:19 pm

Great post Danespirit...this should be a sticky. I really like the .gif too...it kinda' brings it all to life. Thanks.
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Re: Hydrometer

Postby Danespirit » Tue Aug 18, 2015 9:27 am

Thanks..
I notice this subject was coming up a few times the last days and a HD google search only came up with Bushmans post and a few others.
None of them was going into details, so i thought i might contribute with a little in here.
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