Brix conversion

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mysterio

Brix conversion

Post by mysterio » Mon Jan 22, 2007 2:03 pm

I just took a refractometer reading of beer that has been fermenting since Friday (the initial vigorous fermentation looks like it has subsided). It came out at about 12.3 which is around 1.050 SG I think.

This is strange because, although I couldnt take an OG (I smashed my hydrometer), it was supposed to be around 1.044 when I pitched the yeast. I may have messed up my volumes a bit because it was a 10 gallon batch - but not too much I dont think.

Any ideas?

Either A) I don't know how to work the refractometer; B) I wildly miscalculated and made something like a 1.060 ale and its only dropped a few points over the weekend - maybe what I thought was vigorous fermentation was just the growth phase; C) I should relax, dont worry etc.

steve_flack

Post by steve_flack » Mon Jan 22, 2007 2:20 pm

Refractometers are designed for sugar solutions. The presence of alcohol in a fermenting beer affects the readings as alcohol is less dense than water but the refractometer doesn't see it in the same way as a hydrometer - consequently it's not a linear relationship. In fact it's probably the most complicated bit of maths I've seen related to beer. I'd use a software program if you have one or ask nicely someone who has...

steve_flack

Post by steve_flack » Mon Jan 22, 2007 2:26 pm

If you fancy hurting your head here's the formula

Code: Select all

Specific Gravity from original and final Brix

SG = 1.001843 - 0.002318474*OB - 0.000007775*OB*OB - 0.000000034*OB*OB*OB + 0.00574*FB + 0.00003344*FB*FB + 0.000000086*FB*FB*FB

          where:

                   SG = estimated specific gravity of the sample
                   OB = Original Brix
                   FB = Final Brix

mysterio

Post by mysterio » Mon Jan 22, 2007 2:34 pm

Ah I see. Beersmith seems to do the calculation.

I dont know the OG so it's not much use :roll:

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Andy
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Post by Andy » Mon Jan 22, 2007 2:40 pm

Why didn't you use the refractometer to take the OG :?:

As Steve mentions the calculations for unfermented wort and fermenting wort are different when you use a refractometer so best let the s/w do the maths 8) (don't forget to select the correct option though e.g. unfermented, fermenting etc).
Dan!

mysterio

Post by mysterio » Mon Jan 22, 2007 2:45 pm

It just arrived in the post today, ordered it on Thursday. Pretty fast from Hong Kong.

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Post by Doingatun » Mon Jan 29, 2007 9:51 pm

Hi All – Just received refractometer from Hong Kong and playing with known hydrometer readings using Beersmith Refractometer Tool, would somebody please explain what you have to enter in the boxes for Finished Beer Calc ABV/OG – entered 5.6 Brix for finished Beer do you have to take an FG hydrometer reading also? missing the point.

mysterio

Post by mysterio » Mon Jan 29, 2007 10:09 pm

In very basic terms, as far as I understand it: the refractometer is for measuring the sugar in liquid, so, you can take a reading before fermentation and convert the brix into the SG.

However with finished or fermenting beer, the brix number won't convert to SG because it's a mix of alcohol and sugars. So, beersmith will do the calc, presuming you know the original gravity.

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Post by Doingatun » Mon Jan 29, 2007 10:16 pm

Yes I've an SG1.038 and an FG1.012 but I don't understand why you have to enter a FG hydrometer reading along with a brix to get Beersmith to give the abv etc

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Post by Andy » Mon Jan 29, 2007 10:19 pm

I never use the "finished beer" option - that's used to work out what the OG was (if you didn't record it) given the FG brix and FG measured using a hydrometer.

I use "unfermented wort gravity" option to measure the gravity of the wort before yeast is pitched....

and then "fermenting wort gravity" to take daily readings as the beer ferments (you need to have recorded the OG for this calc).
Dan!

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Post by Doingatun » Mon Jan 29, 2007 10:30 pm

Thanks Andy - Mysterio, I understand now :roll: .

Cheers

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