I brewed my first shot at a Belgian Saison two weeks ago (SG=1.057). A week ago it was at 1.005 on the hydrometer and the Milwaukee 884 digital refractometer said 5.7 which calculates to 1.001 using the Northern Brewer online calculator.
I followed some good advice from the Forum and let it go another week. Hydrometer now reads 1.002 and the refractometer now says 4.8 (calcs to 0.996).
It’s a cheapo hydrometer but I calibrated it about a year ago with distilled water.
The two agreed on the SG but are far apart on the FG. Do refractometers not work well down there? Is NB calculator suspect in that range? Something else going on?
Did you take an OG reading with the refractometer as well? If the hydrometer is off by a couple of points, this is going to increase the discrepancy of the FG calculator.
I do think the traditional calculator tends to predict low for beers that are highly attenuated.
The refractometer correction calculators are all slightly suspect. Sean Terrills is pretty accurate over a wide range but you have to have the wort correction factor to make it work right. this requires measuring OG with a hydrometer and refractometer.
I think Sean’s site has an explanation of wort correction factor. IIRC, refractometers are calibrated for sugar solutions from fruits, which have a different sugars than wort, hence wort correction factor.
Yep, good for OG and you don’t have to toss a lot of beer when taking daily FGs to see when a beer is finished fermenting. But it looks like hydro if you want to know the FG.
I like to look at it from a different perspective. The wort correction factor is based on the fact that different sugars (carbohydrates) have different molecular weights. Depending on your grist, mash schedule, composition of sugars in the final beer (unattenuated simple sugars vs unfewntable dextrines), the weight vs refractory index will diverge.
But, for a given style of beer, with similar grist, mash profile, and yeast, the refractive index should be a very valid comparison. So you can think of it as a reading of its own, vs a means to convert to gravity. If anything, the refractive index is less sensitive to alcohol and is a more definite measurement of sugar content, so it’s more absolute. If you have a Saison and raise the OG by 10 points, the same FG will actually have much more sugar since it’s an overall average of density (high for sugar and low for alcohol).
Brix refractive index isn’t a commonly published number, which is why I like to measure as many commercial beers as I can. Comparing your Saison to Dupont or another classic style is very useful, even without converting to gravity.
Right, although like narvin said one data point is generally sufficient to establish a reasonable WCF for your brewhouse. Really, though, I’ve only seen WCFs range from about 1.00-1.06, so guessing isn’t going to cost much in terms of accuracy.
I guess it just depends on what kind of accuracy you want/need in your brewery. I honestly stopped comparing against a hydrometer after a while, but for those 30 batches the mean deviation is 0.0002 SG, standard deviation is 0.0014 SG, and maximum deviation is 0.0039 SG (that was for an 11% ABV barley wine). About the same as the $10 triple-scale hydrometers we all started out with.