I thought I had this figured out but my last couple of batches are falling way short from my stated SG. My last two batches were identically 0.6 too low in gravity as read with the refractometer. For example, I read 12.6 Brix (approx 1.052) with my refractometer but the hydrometer reads 1.049 (approx 12Brix). My starter read 1.032 (approx 8 Brix) with the hydrometer but reads 8.6 Brix (approx 1.035) with the refractometer. Can’t I just ‘re-calibrate’ my refractometer by dialing in an 8 Brix reading when I read my starter which was at 8.6 Brix?? ??? please help, and thanks, cheers!!
I think you have issue with your conversion formula because 12.6 Brix is about 1048.
What formula are you using?
Thirsty_Monk, that could be. I tried using a chart on another forum but it was further off than the following formula. I searched the net until I found the following formula which I have been using:
SG = 1.000898 + 0.003859118B + 0.00001370735BB + 0.00000003742517BBB
where:
B = measured refractivity in Brix
SG = calculated specific gravity at 15 C (59F)
any further help would be greatly appreciated… thank you
I think there was just discussion on this forum about formula to convert brix to Plato and to original gravity.
I am not a big formula guy.
I use ProMash where I enter Brix and it will do conversion.
You could also check More Beer refract spread sheet that is pretty accurate.
http://morebeer.com/learn_vids/vids_refract
Are you writing your own program/spreadsheet?
Thirsty, I believe you are correct in that I am using the wrong conversion table. After watching the morebeer video, it stated that 15 Brix = 1.060 gravity. According to my chart, I show 15 Brix = 1.062 gravity, while the older chart showed 15 Brix = 1.063 gravity. On my chart, 1.060 gravity = 14.5 which is darn well near the 6 Brix I am always off. What formula or what chart is everyone else using?? :-\
Check also this thread:
http://www.homebrewersassociation.org/forum/index.php?topic=1258.msg15845#msg15845
Ok, on the morebeer site I downloaded the spreadsheet and the formula for the BRIX to SG conversion. Unfortunately, it appears that whichever formula one uses, will determine how far off their conversions will be. Taking the lower variables from my original formula and the newer formula (from morebeer spreadsheet) and applying them, morphs into yet another formula which further adjusts the conversions getting my readings closer to what my hydrometer is saying. Since I am no mathematician, I found myself wanting to further ‘enhance’ the formula so that my refractometer actually equates with my hydro reading. Fortunately, I caught myself, and now am wondering why they just do not make a refractometer that reads gravity like a hydrometer. Wouldn’t that be the best of both worlds? Is that even possible? 
Yes, that is possible but you have to keep in mind that the market for this refractometer is limited to brewers as it would only read the correct gravity for brewer’s wort. It may even be so limited that it only reads the correct gravity of all malt brewer’s wort. All it takes is a replacement of the scale mounted inside the refractometer.
Much less confusing would be a refractometer that reads the refractive index and you would use a table to convert it to the wort specific gravity. This is pretty much what you do now only that the refractive index is expressed as the sugar content (Brix) of a sugar solution that has the same refractive index as you sample.
Kai
Is it possible you’re simply forgetting to apply the wort correction factor?
12.6/1.04 = 12.1 → 1.050
8.6/1.04 = 8.3 → 1.034
The thread Thirsty_Monk linked to gets into this.
there is a refractometer that reads gravity, I have one, it reads brix-scale on left side and gravity-scale on the right side. i just calibrate it to read same as my hydrometer, i can check my runnings at any time and see reading in gravity-scale.
Even if it reads gravity it may not be the same gravity that you measure with a hydrometer if you use wort. Chances are that it reads the correct gravity of a sucrose solution.
Kai
The refactometer i have is for use for beer only, it measures gravity of wort, same as a hydrometer. its out in my backyard brewery, i’ll tell you the details tomorro, its raining here now.
the same one i have is on e-bay, the item # is (370317544138)
That’s sweet but for the upcharge, I’ll use the spreadsheet and convert from Brix. :o