Refractometer for FG

Hi fellow brewers,

Do any of you monitor gravity readings with a refractometer at the end of fermentation? I do 3 gallon batches in 6 gallon fermenters, and my thief can't even extract enough of a sample for my hydrometer to measure. Plus taking a hydrometer sample for a 3 gallon batch takes too much beer :cross:

I know it's possible to use brix for FG, but the alcohol skews the readings. Any advice? Thanks!

I do. Theres plenty of calculators online for reading the FG with it. Plus Beersmith has a tool for it.

Personally, I think it can be slightly off due to human error in reading it. However, I don't really care what the actual ABV is in my beer, as long as I have some sort of idea. I do still use my hydrometer from time to time though.

You can do it if you're not desiring absolute precision, use this: http://seanterrill.com/2012/01/06/refractometer-calculator/

It works, but take an hydrometer reading when you finally bottle.

I think there is a lot of error in refractometer readings, that I don't take them after the OG reading.

Once fermentation is started, I usually only take 1 reading; A day before bottling. If it is where I expect it to be, I bottle, if not, then I think about what I need to do, if anything.

I know a lot of folks refer to the Sean Terrill site and all of his explanations for it. However, my own Hydrometer tests against my refractometer readings are, and have always been, in sync with this much simpler online calc.

http://onebeer.net/refractometer.shtml

You shouldn't take my word for it and you should do your own tests. All I can say is that for me, I have done a Hydrometer to Reftactometer OG/FG test on several occasions and I have found the onebeer.net tool was dead on the money every time. Enough so that I don't even bother testing any more. I just use the tool and I trust its conversion.

I've never once had a refractometer reading match a hydrometer reading for FG, even with various correction software. Some are close-ish, but not exact.

I use a refractometer for pre-fermentation, and a hydrometer for post fermentation, even with my wines.

Yooper said:

I've never once had a refractometer reading match a hydrometer reading for FG, even with various correction software. Some are close-ish, but not exact.

I use a refractometer for pre-fermentation, and a hydrometer for post fermentation, even with my wines.

Click to expand...

To be clear, it's not the actual post fermentation readings that have matched. Its the calculated FG from pre-fermentation brix to post fermentation brix based on the OneBeer.net tool. Again, this has been my experience....

I used the Sean Terrill spreadsheet and checked against my hydrometer and found it was pretty damn accurate. When I dropped my (5th?) hydrometer last year I never replaced it!

FWIW & YMMV and WTF etc.

Cheers!
Steve da sleeve

Yooper said:

I've never once had a refractometer reading match a hydrometer reading for FG, even with various correction software. Some are close-ish, but not exact.

I use a refractometer for pre-fermentation, and a hydrometer for post fermentation, even with my wines.

Click to expand...

How close is "close-ish"? The few time I've compared, they've been within a point or two. Unless you're using a lab grade, narrow range hydrometer, that's about as accurate as you can read the instruments anyway. My hydrometer is good for +/- 1 gravity point before any temperature corrections. And although others claim otherwise, I'd say .25 Brix is about as close as I can get on my refractometer.

That said, the only time I really use a refractometer after pitching the yeast is to monitor a lager fermentation to decide when to start the d-rest. I like to have a taste before packaging anyway, so it's no big deal to use a hydrometer for my final final gravity reading.

gr8shandini said:

And although others claim otherwise, I'd say .25 Brix is about as close as I can get on my refractometer.

Click to expand...

Roger that....

For those of you who take refractometer readings of the finished beer, what kind of pipette do you use to retrieve the sample? I need one that is long enough to reach down into the beer. Three gallons of beer fills up about 2/3rds of the fermenter I use.

A small change in the final Brix reading makes a huge change in the calculation. Using the Onebeer calculator that Nagrog posted:

14 Brix -> 8.00 Brix, you have 5.45% ABV
14 Brix -> 8.25 Brix, you have 5.25% ABV

8.0 Brix or 8.25 Brix are 1.032 and 1.033 gravity points, respectively. You can be more precise with the hydrometer. If you are measuring freshly boiled wort and just fermented beer at significantly different temperatures, the ATC on the inexpensive refractometer is another source of error.

satph said:

A small change in the final Brix reading makes a huge change in the calculation. Using the Onebeer calculator that Nagrog posted:

14 Brix -> 8.00 Brix, you have 5.45% ABV
14 Brix -> 8.25 Brix, you have 5.25% ABV

8.0 Brix or 8.25 Brix are 1.032 and 1.033 gravity points, respectively. You can be more precise with the hydrometer. If you are measuring freshly boiled wort and just fermented beer at significantly different temperatures, the ATC on the inexpensive refractometer is another source of error.

Click to expand...

To be fair, the example you cited translated into SG is:

14 Brix -> 8.00 Brix, you have 1.0158 FG (Call it 1.016?)
14 Brix -> 8.25 Brix, you have 1.0174 FG (Call it 1.017?)

To me, that's also a pretty close read on a Hydrometer.. Seems like splitting hairs really and I guess I don't get bent out of shape over a .2 % variance in ABV..

You can always take a Brix reading, and not bother to convert it to SG. When the Brix reading stays stable for 2 - 3 days, fermentation is finished. You can then use a calculator to get an approximation of the FG, or use a hydrometer just once to get an accurate FG.

-a.