Author Topic: Hydrometer Readings  (Read 308 times)

Offline porkchopexp2

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Hydrometer Readings
« on: March 24, 2018, 01:28:03 PM »
Conducted my first BIAB, and first all grain for that matter.  I took a pre-boil hydrometer reading.  I left the hydrometer in the same wort sample I took for my pre-boil reading the was higher than the first reading.  I took a post boil reading after topping off to my desired total of wort in my fermenter and the same thing happened, after about 10-15 mins the hydrometer was reading a higher number than before.  Which reading should I use, an any ideas whats happening?

Offline Robert

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Re: Hydrometer Readings
« Reply #1 on: March 24, 2018, 01:37:37 PM »
Are you correcting for temperature?   Solutions get less dense as they get warmer, so as your sample cools it gets denser (higher gravity.)  You have to take the temperature of your sample and correct the reading to the temperature your hydrometer is calibrated at (either 59°F or 68°F usually.)  Your hydrometer should have come with a chart showing how much to add or subtract at any other temperature to get the actual gravity, and should be marked showing the calibration temperature.   If you don't have a chart, search for hydrometer correction, there are calculators out there. The actual gravity will not have changed, just the apparent reading at different temperatures.
Rob
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Offline dmtaylor

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Re: Hydrometer Readings
« Reply #2 on: March 24, 2018, 01:49:17 PM »
The higher the temperature, the lower the gravity reading.  You should always try to measure between 60-70 F if you can manage it.  Otherwise there's a table somewhere's that can help you adjust the reading for temperature.
Dave

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Offline porkchopexp2

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Re: Hydrometer Readings
« Reply #3 on: March 24, 2018, 03:32:10 PM »
Thank you, I have no idea what my hydrometer's calibration temperature is.  I did  look up the calculator on brewers friend and used 68 F as calibration temp.   

Offline Robert

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Re: Hydrometer Readings
« Reply #4 on: March 24, 2018, 03:45:27 PM »
Thank you, I have no idea what my hydrometer's calibration temperature is.  I did  look up the calculator on brewers friend and used 68 F as calibration temp.
Maybe the shop where you bought it can tell you the temp.  The cheap homebrew ones seem to be most often calibrated around 60°F, while the more professional.ones ate at 68°F/20°C.  Anyway, even using the wrong scale you'll still be off by less than 0.002.
« Last Edit: March 24, 2018, 07:40:00 PM by Robert »
Rob
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Offline personal brewer

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Re: Hydrometer Readings
« Reply #5 on: March 24, 2018, 08:43:45 PM »
I use a cheap homebrew one that is theoretically calibrated to 60 degrees F.

You can check actual calibration by using distilled water at the proper temp.

Mine however checked out .001 under and after using the manufacturer supplied temperature correction chart for 68 degrees F, turned out to be .002 under.

Instead of trying to remember to correct each reading by .002 and then later trying to remember if I applied correction or not I just read SG at room temp, record the reading and remember everything in my records should be .002 over.

It has been easy enough to chill the cylinder by putting in a tall water glass and surrounding with ice cubes until  68 degrees has been reached. Which is where my thermostat is at this time of year. Dunno what I will do when summer comes and I set the thermostat to 72 degress F.  Probably won't worry about it very much.

I do take readings and pour the wort back in, until post boil.

I have an inexpensive refractometer. Just doesn't seem very accurate to me. When one website did a synopsis on how many readings you had to take, record and evaluate to get a correction table it just didn't seem to me to be worth the effort.

Offline hackrsackr

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Re: Hydrometer Readings
« Reply #6 on: March 25, 2018, 01:49:38 PM »
Thank you, I have no idea what my hydrometer's calibration temperature is.  I did  look up the calculator on brewers friend and used 68 F as calibration temp.

Look on the hydrometer at the very bottom of the paper scale toward the glass bulb. Should give you the calibration temperature. Should say something like sp. gr. 60 @ 15c/60f or 20c/68f. That’s the temperature you want to measure at. Although the difference is minor, it’s still nice to know, especially for FG readings.




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