Refractometer issue

[TheDarkSide]

Here's the formula:

=IF(A11>0,(1.001843-0.002318474*(A$7)-0.000007775*(A$7^2)-0.000000034*(A$7^3)+0.00574*($A11)+0.00003344*($A11^2)+0.000000086*($A11^3))+(1.313454-0.132674*B11+0.002057793*(B11^2)-0.000002627634*(B11^3))*0.001,0)

See how simple it is

Here's the link to the spreadsheet. You just need to know what your starting gravity is:

http://morebeer.com/public/beer/refractbeer.xls

[mthhurley]

How can the refractometers reading be adjusted after fermentation if the final gravity is unknown, and may be off of what is expected?

Can you describe how the post fermentation adjustments work?

Because I'd love to use a Refractometer instead of a Hydrometer

Essentially, the measurement you are taking IS your FG...at that moment.

I've only used a refrac so I've been comfortable with it since day one...However, I went through this exact question when I couldn't figure out why my FG's were so high. It was definitely a "DOH!" moment.

[ajdelange]

How can the refractometers reading be adjusted after fermentation if the final gravity is unknown, and may be off of what is expected?

Can you describe how the post fermentation adjustments work?

It is properly done by calibration. To quote the ASBC's MOA Beer-5 "Differences in real extract and alcohol contents of beers usually make a calibration curve necessary for each type of beer analyzed." As I noted in an earlier post, if you are a commercial operation that has a Kölsch in its portfolio you oviously brew this frequently. You take refractometer meaurements and digital densitometer measurements for AE, TE and alcohol and construct calibration curves for your Kölsch. After enough beers have been analyzed in this way and the residuals of the calibration curve(s) have been determined to be acceptable you can, in the future, omit the laborious analysis and simply read the RI and insert it into the calibration curve thus obtaining AE, TE and ABV for the Kölsch. Similar curves need to be developed for the other beers in the portfolio. If all you care about is AE then obviously you can generate calibration curves yourslef by comparison with hydrometer readings. As with the digital density meter the criterion for acceptance would be tolerably low residuals (how low is really up to you to decide).

It is, of course, possible to generate an average curve from a set of calibrations for different beer styles and obviously the formulas out there attempt to do this. In many cases they work and in many cases they don't. The difficulty is that you have no way of knowing whether you have one of the cases that does on one that doesn't. If you make the calibation curves and the residuals look good then you can procede with the RI approach. I suspect that in home brewing the controls are not good enough to allow a tight calibration to be done.

If you are trying to use a single formula to "correct" an RI reading for alcohol you are fooling yourself unless and error of 1 - 2 °P is acceptable.

Because I'd love to use a Refractometer instead of a Hydrometer

Yes, wouldn't we all? Refractometers are great for monitoring the decline in extract content as the sparge progresses and for detecting the cessation of fermentation but not for much else. They are not a replacement for a hydrometer.