Refractometer adjustment for fermenting wort

Beersmith has a tool to convert your refractometer reading to SG. I have 3 options. The first is unfermented wort, second is fermenting wort, and finished wort.

My question is why the conversion? My SG comes in much lower with the conversion than the unfermented wort conversion. Is it because the alcohol bends the light differently and that needs to be compensated for?

Sorry, first batch with a refractometer (it is an ATC, BTW).

Side note, I don't know if it will help. I am fermenting a light lager. My OG was 9B and now it is 3.9B (1.035 -> 1.004), this is a week into fermentation. Tastes ok, no sour flavors noted, predominant malty sweetness, color pale with good clarity.

reim0027 said:

My question is why the conversion? My SG comes in much lower with the conversion than the unfermented wort conversion. Is it because the alcohol bends the light differently and that needs to be compensated for?

Click to expand...

Yes.

And the conversions with the various programs are not always accurate. You're better off using a hydrometer for ferementing and feremented wort.

Hmm. Maybe I'll do a few side-by-side comparisons, checking Beersmith's accuracy. Thanks bro.

Here's some more info:

http://seanterrill.com/2010/06/11/refractometer-estimates-of-final-gravity/
http://seanterrill.com/2010/07/20/toward-a-better-refractometer-correlation/
http://seanterrill.com/2011/04/07/refractometer-fg-results/

I haven't used any of this yet, so I don't know how accurate it is, just thought it might be of interest.

Great, I'll check them out. I'm about ready to take a hydro reading (letting the sample warm up) to check my Beersmith. I'll read those articles. More info is always better.

When I need to determine if fermentation is complete, I use the refractometer and take a Brix reading (but don't try converting to SG. When the Brix reading stops dropping, fermentation is done, and I can take a single hydrometer reading to get an accurate result.

Sean Terrill's calculator has been the least inaccurate calculator that I have found, but it still isn't as accurate as the hydrometer.

[Doh] Didn't realize how old this thread was. [/Doh]

-a.