Refractometers for FG readings?

Yes, refractometers can be used for both OG and FG readings. In both cases, use a refractometer calculator to convert from the "brix" reading to specific gravity. The original and final readings are both needed in the same calulator. i.e. don't try to compute an FG specific gravity without having the original reading too.

 

Yes it works. Use Sean Terrill's calculator: http://seanterrill.com/2012/01/06/refractometer-calculator/

In my experience it's accurate when checked against both hydrometers and vibrating U densitometers.

 

I do it all the time. There are people who will insist that it's not useful for FG. Those people are wrong.

 

In my experience my FG is -/+ .005 when checked against a hydrometer.

 

when i first got my refractometer I used Sean Terril's calculator and checked it against my hydrometer. Always accurate, but I will say that the tiny sample size of a refractometer is both a strength and a weakness.
You can take samples from different places in the wort or beer and get different readings. A 100-200ml hydrometer sample is more likely to get a representative reading. Make sure you're not taking a sample from the very surface of the beer. stick your pipette in a few inches.

these little caveats aside, my refractometer was a great purchase and I highly recommend one.

 

I have problems with the repeatability of my refractometer. Hygrometer readings sways make sense, but occasionally I get a flakey reading with the refractometer (ADE Advanced Optics Beer Wort and Wine Refractometer, Dual Scale) I got from Amazon. At the present time, having to double check with the hydrometer is defeating the purpose.

 

I second Sean Terrill's calculator = close enough!!

 

If you have software like BeerSmith it has a refractometer calculator tool built in. That's what I use.

 

Aside from the accuracy debate, can you depend on a hydrometer for consistency in FG readings? I'm currently monitoring a funky/sour saison for bottling and was wondering if the margin for error could hide slight fluctuations in gravity?

 

Don't use the dual scale thing. Translate the Brix into SG with a calculator. It's better.

 

The problem is not a scale issue. I get 20 point variations when taking one reading after another. I have a pretty scientific background, so reading the refractometer (or other "instruments" is familiar territory. If I re-check with water, it's on the spot (1.0000).

My next step was going to be a gage capability study with sugar solutions.

 

If your background is in science you've probably already considered this but are you using a wet pipet? If the pipet is wet from starsan or something it can throw off the reading a lot cuz you are only measuring from a few droplets. I always draw and release several times before taking the sample I test, so that the wort and only the wort is what I'm measuring.

 

Yeah, you gotta be really careful to wash it off, dry, wash, dry, then take your next reading. Don't want any residuals from last reading or water to dilute.

 

Another two thumbs up for Sean Terrill's calculator. I checked the results of his calculator vs hydrometer for a number of beers; the calculator is quite accurate: I compared readings on 19 beers, the standard deviation between by hydrometer and (corrected) refractometer readings is 0.0006. I don't use the hydrometer anymore.

There are a couple of caveats. (1) The correction is for all malt beers, so a lot of simple sugars will throw things off. (2) For (typically big) beers with a FG > 1.020 the correction does not work very well.

Cheers!

 

Two more thumbs up. Sean Terrill's calculation is best one I've seen, which is why I incorporated it in BrewCipher.

Regarding a lot of simple sugars throwing things off, that's where Sean's calculator's "Wort Correction Factor" (WCF) comes in. Unfortunately, there's no intuitive way to set the factor for various worts, so most people (I think) just leave it at Sean's default value (1.04). So in BrewCipher, I added a recommended WCF, based on the expected attenuability from the recipe. I have found it to work pretty well, but there's also still the option to override the WCF with Sean's default, or any value the user wants.

 

FWIW, I rinse the pipette about 6 times with water, then rinse about 6-8 times with the next sample taking care to make sure that all surfaces that were wetted before are "refreshed". Once or twice, it seemed that I heard something flopping around inside the refractometer...maybe I just have a defective one. Anyway, thanks for the comments. Eventually I'll nail it down to some quirky method problem or a defective instrument. Prost!

 

Does Sean's calculator only work in the FG range, or is it reasonably accurate for intermediate readings as well? The reason I ask, is that I'd like to be able to use the refractometer for determing when to do the diacetyl reast.

 

It's good for any reading along the way, as long as it's paired with the OG reading.

 

Thank you. I hadn't known before today that the refractometer readings didn't work directly. I had been taking readings for a diacetyl rest and couldn't figure why I was still getting such high readings (double what I expected) until I found this thread. I missed the diacetyl rest by a long shot as a result.