Author Topic: Refractometer FG Calculator (now with PHP!)  (Read 2783 times)

Offline a10t2

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Refractometer FG Calculator (now with PHP!)
« on: January 07, 2012, 10:07:01 AM »
I've had quite a few requests, so I figured I'd post something to let people know it's finally done.

Refractometer Calculator

Any help with error checking and such would be appreciated. Cheers!
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Offline narvin

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Re: Refractometer FG Calculator (now with PHP!)
« Reply #1 on: January 07, 2012, 11:28:59 AM »
Awesome!  Thanks, I've found your spreadsheet to be very accurate so far.
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Offline benamcg

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Re: Refractometer FG Calculator (now with PHP!)
« Reply #2 on: January 28, 2012, 01:12:57 PM »
Thanks for the spreadsheet- it definetely helps sort out a bunch of confusion I am having with this instrument.  Can someone explain why a refractometer if only good for pre-fermentation readings. I did not see instructions for only using the refractometer pre fermentation, but now I do notice the "SG wort" label under the specific gravities. Does yeast in suspension bend light that much to throw off the FG readings?

Offline denny

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Re: Refractometer FG Calculator (now with PHP!)
« Reply #3 on: January 28, 2012, 01:14:06 PM »
Thanks for the spreadsheet- it definetely helps sort out a bunch of confusion I am having with this instrument.  Can someone explain why a refractometer if only good for pre-fermentation readings. I did not see instructions for only using the refractometer pre fermentation, but now I do notice the "SG wort" label under the specific gravities. Does yeast in suspension bend light that much to throw off the FG readings?

It's because alcohol has a different SG than water, which throws off a direct reading.
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Offline tschmidlin

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Re: Refractometer FG Calculator (now with PHP!)
« Reply #4 on: January 28, 2012, 01:35:22 PM »
Thanks for the spreadsheet- it definetely helps sort out a bunch of confusion I am having with this instrument.  Can someone explain why a refractometer if only good for pre-fermentation readings. I did not see instructions for only using the refractometer pre fermentation, but now I do notice the "SG wort" label under the specific gravities. Does yeast in suspension bend light that much to throw off the FG readings?
Denny means the the alcohol has a different refractive index than both water and dissolved sugar, which throws off a direct reading.

If plain water is set to zero (by calibrating the refractometer) you could read a mixture of water with either alcohol or sugar.  But in a mixture of all three you can't tell how much refraction is from alcohol and how much is from sugar.  If you have a base reading before fermentation then you can use an equation to determine alcohol content, but in general a hydrometer is easier and more accurate.  Sean's spreadsheet is very good, most of the others are off significantly in practice.
Tom Schmidlin

Offline denny

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Re: Refractometer FG Calculator (now with PHP!)
« Reply #5 on: January 28, 2012, 03:46:24 PM »
Denny means the the alcohol has a different refractive index than both water and dissolved sugar, which throws off a direct reading.

Yeah, that's what I meant!  First day off the painkillers, but my mind still isn't working right.
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