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-   -   Hydrometer v refractometer readings for final gravity (http://www.homebrewtalk.com/f163/hydrometer-v-refractometer-readings-final-gravity-192014/)

hiphops 08-21-2010 03:10 PM

Hydrometer v refractometer readings for final gravity
I took a measurement of my pale ale to determine it's final gravity. The hydrometer read 1.008 and the refractometer read 1.017. (it's beeen fermenting for about 20 days now and had an original gravtiy of 1.040)

I was told that for final gravity purposes to rely on the hyrdrometer and not the refractometer.

Is that right?

Also, to the extent you can comment on thus, what do you make of these readings?

JNye 08-21-2010 03:30 PM

use the hydrometer. The alcohol that is now present in your beer is skewing the reading from your refractometer. The number from the refractometer can be adjusted with a formula, lots of online calculators out there for this. I don't have a link, I use Beersmith for the conversion.

JuanMoore 08-21-2010 03:43 PM

Alcohol distorts refractometer readings, so you need to use a formula (like this spreadsheet) to correct for the presence of alcohol after fermentaion has started. Even after making the corrections, it still won't be very accurate, so anything post fermentation is better to rely on the hydrometer.

Using the info you gave, I'm guessing the original refractometer reading was around 10.1 brix, and the final refractometer reading was around 4.25 brix. If that's the case, the corrected FG would be 1.004, which is closer to the hydro reading, but still not very accurate.

kappclark 08-21-2010 10:55 PM

I just want to have a readable hydrometer ! Glasses help, of course, but does anyone use a hydrometer built exclusively for checking finishing gravities ?

JuanMoore 08-21-2010 11:52 PM


Originally Posted by kappclark (Post 2230270)
I just want to have a readable hydrometer ! Glasses help, of course, but does anyone use a hydrometer built exclusively for checking finishing gravities ?

Many soil hydrometers have a fairly narrow range that would work well for measuring FG. A lot of them measure in g/L, but some measure 0.995 - 1.038 SG. Here's the cheapest one I could find with a quick search-http://www.humboldtmfg.com/showitem-336.html

ajf 08-22-2010 02:02 AM

Yes, I do. You can get "finishing" hydrometers that have a very narrow range. Mine reads from 0.990 to 1.020, and it is easy to read.
I tried ordering one on line from Norther Brewer. It arrived snapped in two, but they replaced with another one that was also snapped it two. They offered to replace it with another one, but refused to pack it properly so that it would arrive intact. I then ordered one from Austin Homebrew that read 0.005 high. i.e. I couldn't read a gravity > 1.015. Then I bought one from my LHBS, and it is accurate. I've been using it ever since and am very happy with it.


tdawg183 11-15-2012 07:53 PM

I believe I know the answer to this but does the same apply to final gravity wine readings?

jgaepi 11-15-2012 08:02 PM

I know the equipment just adds up and takes up space but the most accurate option for OG is a refractometer and don't skimp on the price (buy at least the $50 ones and must account for ATC) and then the hydrometer for FG. More equipment but the best for accuracy.

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