Refractometer malfunction

[Crut]

I'm confused.

that happens to me all the time!
-Crut

[Mylo]

Jay, I think the correction factor that you are referring to (in Promash) is different from the "Fermenting Wort" specific gravity calculations. I don't know why it would be .4 - I can't see any correlation.

I know in BeerSmith, you calibrate the correction factor for your refractometer. You do this by not only zeroing out the rfm with water - but by comparing the brix reading on the rfm with the value from your hydrometer, using a sample of unfermented wort. I think that is to fine tune the correction for your specific rfm. My correction value (not changed from the default is 1.0286.

There is a rfm tool in BeerSmith that asks for your OG (in Brix), and your FG - and will determine your corrected FG. I assume that it's calculations are identical to what appears in the spreadsheet from B3.

Good luck.


Mylo

[BDawg]

There are 2 correction factors here:

1) Brix does not equal Plato. You divide Brix by 1.04 or somethign like that and it gives you the Plato value.

2) The deal with the FG correction factor is that alcohol will bend light (refract) it differently than water. These gizmos measure how much the light bends. When there's more sugar in the water, the light bends a different amount. That works great for an OG, where there's basically water and sugar dissolved in there (solids don't change the bend). You can read the value directly.

Now, after the beer ferments, there's less sugar in there to bend the light, but there's also alcohol in there too, which bends it differently from the water. And that's what screws things up. Different amounts of alcohol will bend the light differently. But there is is still some sugar in there too, causing the light to bend differently. So, some of the bend comes from the alcohol, and some from the residual sugar. We need to figure out how much of the effect is from each of the components.

If you know what the OG was, you know how much sugar was there to begin with, and it can help you zero in on a really good estimate of how much alcohol there is in there now that it fermented. They did this by measuring a gazillion samples with both a hydrometer and a refractometer until they had enough samples that they could figure out a formula that uses both the numbers (OG, and the Measured Brix level) when you run that through a formula, it comes up with the right FG.

Bottom line, the software can figure out your FG if you give it the measured final brix reading AND the measured OG Brix reading.

HTH-