Author Topic: hydrometer vs. refractometer readings  (Read 1559 times)

Offline Beer Sense

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hydrometer vs. refractometer readings
« on: May 13, 2014, 01:53:13 PM »
I bought a refractometer recently to make my gravity readings easier and less costly in terms of wasted beer.  I calibrated it to 1.000 using distilled water at room temperature. I also put my hydrometer in distilled water and got a reading of 1.002.  taking a sample from the same beer, my hydrometer would get a reading of 1.012, which I would read at 1.010 given it was .002 over on the calibration.  With the same beer, my refractometer would read 1.020.  How could they be that far off?  same beer, same temperature.  Thoughts?

Offline Stevie

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Re: hydrometer vs. refractometer readings
« Reply #1 on: May 13, 2014, 01:57:21 PM »
Are you sampling beer or wort? Even with the various formulas, I have never been able to match a refractometer to a hydrometer when measuring beer. Another thing you should do is make a dropper bottle of 10% sugar solution with distilled water (measured by weight). This allows you to measure at two points when calibrating.

Offline dcb

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Re: hydrometer vs. refractometer readings
« Reply #2 on: May 13, 2014, 02:14:57 PM »
I just used a newly-purchased refractometer this weekend and had fun trying it out.   I had to tweak it a bit to get to zero with distilled water, and then verified that my hydrometer also measured 1.000.  I used both to measure first runnings, second runnings, pre- and post-boil gravities.  In every case the two were within .001 of each other.  I'm not even certain my measurement error with either instrument is .001.

The refractometer was one hell of a lot easier to use.  Thanks for the sugar solution idea.  I should have thought of that (or read more).

Offline mchrispen

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Re: hydrometer vs. refractometer readings
« Reply #3 on: May 13, 2014, 02:16:33 PM »
I use my refractometer during lautering and to determine when fermentation is complete (3 days of identical readings).


Otherwise, trust the calibrated hydrometer. It is the correct tool for measuring wort gravity.


Refractometers are tricky, but can be useful. You need to account for differences between beer wort and wine must (maltose v sucrose) and during fermentation - account for alcohol production. You should also be using the Brix reading, unless you can confirm that your device is specifically calibrated for beer. Like Steve, getting matching absolute readings are nearly impossible - so I use my refractometer to determine when a change is occurring and not for critical measurements.


http://seanterrill.com/2010/06/11/refractometer-estimates-of-final-gravity/


Sean has a fairly lengthy set of posts on using refractometers that are very helpful.

« Last Edit: May 13, 2014, 03:47:38 PM by mchrispen »
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Offline morticaixavier

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Re: hydrometer vs. refractometer readings
« Reply #4 on: May 13, 2014, 02:49:48 PM »
I find both sean's and the beer smith adjustment tool to work fairly well. I'd be more concerned I suppose if I cared if I was 1 or 2 points off.

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« Last Edit: May 13, 2014, 04:51:07 PM by morticaixavier »
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Offline bengelbrau

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Re: hydrometer vs. refractometer readings
« Reply #5 on: May 13, 2014, 03:28:31 PM »

"I find both sean's and the bet smith adjustment tool to work fairly well. I'd be more concerned I suppose if I cared if I was 1 or 2 points off."

+1.

A while ago, I compared the hydrometer reading to the refractometer reading, and found that the hydro was consistently 4-5% lower. In checking with a 10% sugar solution (20 grams table sugar brought to a  volume of 200 ml with distilled water) the hydro read 1.034, and the refr read 1.038. Since then, I use only the refractometer. I am looking for consistency and replicability, rather than absolute accuracy