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Advice On Hydrometer And Refract. Readings Please

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symphony1975

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hi,

using a calibrated thermometer i tested my 2 hydrometers in 20 degree distilled water. both read 1.003.

i also calibrated my refractometer, also using 20 degree distilled water.

brewed on the weekend, took samples to measure pre boil gravity and OG. I did my readings with the samples at 20 degrees.

hydrometer read:
pre boil- 1044
OG- 1051

refractometer read:
pre boil - 1041
OG- 1048

a difference of .003 between hydro & refracto.

going by my attempt at calibrating my hydro and the same difference of .003 between instruments with my samples, can i assume that my refractometer is accurate and that future hydro readings i just need to subtract .003 to get an accurate reading?

is this what other people do once they calibrate their hydrometers?

i was concerned when BOTH hydrometers read the same 1.003. coincidence or have i done the calibrating testing wrong?

cheers.......
 

QldKev

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Are you reading the refractometer facing south?
 

Rowy

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May a thousand camels mate upon your fermenter!
 

emnpaul

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To the OP, I'm on my second brew cellar hydrometer and they both read 1002 in 20 degree tap water, give or take a bee's dick. It stands to reason that two hydrometers from the same manufacturer, made on the same equipment will read the same or very close to it. That being the case I'd say your calibration is fine. If they are different brand then maybe have another look at your calibration.
 

manticle

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In the interests of trying to get the guy an answer to the reasonable question he asked, I'll post what I wrote in a PM.

Your testing looks to me very sound.

I should let you know though that I have only just started using a refractometer and am not anywhere near expert on their use.

My understanding is that, depending on the model, they may not always give entirely accurate readings when converted to a gravity scale so I wouldn't assume the refrac is the one to trust.

I would bump your thread to see if you can get more of a response - sometimes the right people miss things depending on time of post and yours seems well thought out and detailed enough that someone should be able to help better than I.

Until then, I would split the difference between the two instruments and assume the real answer is somewhere around .0015

Hope that helps a bit and sorry I can't be more useful but if I don't know something, I won't pretend.
I could be wrong about the above and my camel died from syphilis anyway but hopefully someone can provide some vaguely useful info at some point.
 

Rowy

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Sorry to hear about the Camel mate........were you close?
 

manticle

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Well he got the syph from me so I guess we may have been a bit too close at one point.

Drifted away in later years though.
 

Rowy

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They all do my friend.............they all do (sigh).
 

QldKev

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In the interests of trying to get the guy an answer to the reasonable question he asked, I'll post what I wrote in a PM.
disclaimer: My background knowledge of this is from the cane sugar industry, and not specifically from brewing.

Remember both Brix and Gravity readings are reading dissolved dry solids, and not just sugar. Dissolved solids will effect the Brix / Gravity of a solution, with some other factors effecting the reading differently. Ie. To read the gravity after fermenting has begun using a refractometer we need to take into account the alcohol content. I've posted about this before, but the way we take our readings we can only use them as a best guess, which generally is fairly accurate as our other dissolved solids are minimal.

For a more accurate brix reading to be taken, even using the hydrometer, the sample must first be well mixed, then strained, and at 20c. The sample should then be left in the sample jar for at least 20mins until all foreign matter has subsided. (Try just leaving the hydometer alone for 20mins and recheck your reading)

I would actually lean towards the refrac reading, as it is less slewed by un-clarified wort. You could work out a pseudo purity by:
pseudo purity = clarified refrac reading/gravity using hydrometer x 100.



QldKev
 

gap

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Is the OP reading the hydrometers correctly?
 

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