Stupid refractometer question

Looking into buying a refractometer & read they're inaccurate in the presence of alcohol. So are these only good for OG and preboil, leaving FG for the hydrometer? Is this worth it?

Get one that reads Brix. I don't recommend a refractometer that reads in SG, or a combination SG/Brix.... If you only use it for checking pre boil and post boil it is well worth the cost. As for how accurate they are at FG? Prepare for all the usual answers. You already posted the most popular. I use a refractometer throughout the process including FG and have abandoned my hydrometer.

There are software programs that convert your fG brix so you can get your abv. For the first few after I got a meter for a christmas gift, I measured with both. No real measureable difference between the hydrometer and refractometer with the results. And I have to say the refractometer is far easier on the eyes to read.

I've used a refractometer for brewing and winemaking for a couple years now and I can't imagine going back to my hydrometer. You can get one for about $25 on ebay and if you download the free magic spreadsheet from MoreBeer you can use it throughout fermentation. It's very accurate.

Here are a couple of refractometer calculators to estimate the final gravity and ABV. You need an OG reading to estimate the FG.
http://www.northernbrewer.com/refractometer-calculator/
http://onebeer.net/refractometer.shtml

I have been using a refractometer for only a few weeks and it is much easier, cleaner, and faster than a hydrometer. Agreed that a hydro is more accurate in more cases. Like iaefebs said, a unit that measures Brix is all you need. On every dual-scale unit I have seen, the SG scale is significantly off above 1.050. Maybe there is one and I have not stumbled across it.

I love my refractometer. Use beersmith to calculate ABV. Easy as pie.

I use a combo ATC SG/Brix and I've never had issues, iaefebs why are you not recommending one?

Not to speak for iaefebs, but one thing you need to be careful with when looking at dual scale refractometers is that many use a linear scale that simply multiplies brix by 4 to get SG. This is fine at lower gravities but you'll be further off as the gravity increases.

A shorthand way of converting brix to SG is to multiply brix by 4. For instance, 10 brix times 4 would equal 1.040. It's actually 1.041, but still reasonably close. If you multiply 20 brix by 4 you would assume a SG of 1.080, but it's actually 1.084. The relationship between brix and SG is non linear.

I think buying a dual scale refractometer is fine as long as you find one that assumes this non linear relationship between brix and SG. They are out there. Mine only shows brix, which is fine for me because I'm always plugging the number into a spreadsheet or beersmith and the conversion to SG is right there.

Interesting,my confusion is mine has two separate scales, one brix and one SG and they are separated (two independent scales/bars). I would think they would be independent entities and no different than a brix only.

Edit: this is what my scale looks like:

It's kind of hard to tell from that picture but it looks like that one is fine. Maybe the linear problem generally has been fixed because all of the refractometers I looked at on ebay seem to have the proper scale.

Admittedly, my eyes aren't great but I can't imagine trying to read SG on that thing. Them's some tiny lines and numbers!

EDIT: I take that back. The scale on the refractometers on ebay seem off. 10 brix shows as 1.039 and 20 brix shows as 1.077. I'm at a loss. Time for someone more knowledgeable about this than me to chime in.

Actually I just found mine: http://www.williamsbrewing.com/Product.aspx?ProductId=1758&More=1

Better picture.

jwalker1140 said:

EDIT: I take that back. The scale on the refractometers on ebay seem off. 10 brix shows as 1.039 and 20 brix shows as 1.077. I'm at a loss. Time for someone more knowledgeable about this than me to chime in.

Click to expand...

Mine also, so now I'm getting mad.

EDIT: whoooops! I'm guessing I should have RTFM, there is something called Brix correction factor I need to work on here.

My preference is a brix only scale, it's clean and simple and easy on the eyes. You use it for the whole process from start to finish with a spreadsheet.

jwalker1140 said:

Not to speak for iaefebs, but one thing you need to be careful with when looking at dual scale refractometers is that many use a linear scale that simply multiplies brix by 4 to get SG. This is fine at lower gravities but you'll be further off as the gravity increases.

A shorthand way of converting brix to SG is to multiply brix by 4. For instance, 10 brix times 4 would equal 1.040. It's actually 1.041, but still reasonably close. If you multiply 20 brix by 4 you would assume a SG of 1.080, but it's actually 1.084. The relationship between brix and SG is non linear.

I think buying a dual scale refractometer is fine as long as you find one that assumes this non linear relationship between brix and SG. They are out there. Mine only shows brix, which is fine for me because I'm always plugging the number into a spreadsheet or beersmith and the conversion to SG is right there.

Click to expand...

That would be almost true if the measurements were taken with a pure sucrose solution. (The actual gravity of a 20 Brix Sucrose solution should be 1.08298). If the solution was wort, the gravity reading should be somewhere around 1.077 - 1.078 because of the chemical composition of the wort.

Paulgs3 said:

Actually I just found mine: http://www.williamsbrewing.com/Product.aspx?ProductId=1758&More=1

Better picture.

Click to expand...

The gravity scale on that should be fairly accurate if you are making a typical beer, but it would be inaccurate when making wine where the Brix Correction Factor should be 1.000.

-a.

ajf said:

That would be almost true if the measurements were taken with a pure sucrose solution. (The actual gravity of a 20 Brix Sucrose solution should be 1.08298). If the solution was wort, the gravity reading should be somewhere around 1.077 - 1.078 because of the chemical composition of the wort.

Click to expand...

Thanks for the catch. I originally started using my refractometer for winemaking and even for brewing I still tend to use a spreadsheet that doesn't use a wort correction factor. I should have known better.

Funny thing though, I've plugged 20 brix into several calculators/spreadsheets/apps and each one gives me a different result:

Seanterril.com: 1.080
Beersmith: 1.081
Morebeer: 1.082
Northern Brewer: 1.083
Onebeer.net: 1.084

jwalker1140 said:

Thanks for the catch. I originally started using my refractometer for winemaking and even for brewing I still tend to use a spreadsheet that doesn't use a wort correction factor. I should have known better.

Funny thing though, I've plugged 20 brix into several calculators/spreadsheets/apps and each one gives me a different result:

Seanterril.com: 1.080
Beersmith: 1.081
Morebeer: 1.082
Northern Brewer: 1.083
Onebeer.net: 1.084

Click to expand...

There are two gotchas when converting from Brix to SG.

1. Brix correction Factor
2. Temperature compensation

The Brix correction factor is used to account for the difference between a sucrose solution and wort. Brix is defined as the % sucrose in a solution. Wort contains very little sucrose, but a lot of maltose which has a different refractive index. To get an accurate conversion from Brix to SG, you need to use a pure sucrose solution. If the solution is wort, you divide the Brix reading by the Brix correction factor to compensate for the difference between sucrose and wort.

Temperature compensation is generally necessary because most hydrometers are calibrated to give an accurate reading at 15C (59F), while refractometers are generally calibrated at 20C (68F). If this is not accounted for, it will introduce an error of approximately 0.78 gravity points.

So let's look at your references
SeanTerril:
Change the wort correction factor to 1.00 and you get a true Brix conversion of 1.083 (which is 1.08298 rounded to 3 decimal places). However, he doesn't account for temperature compensation.

BeerSmith:
Use the hydrometer tool to set the calibration temperature to 68F
Then use the refractometer tool to Calibrate Refractometer settings
Enter 20 Brix, and adjust the hydrometer reading until the correction factor = 1.000. You need to enter a SG of 1.08368, so BeerSmith gives 20 Brix = 1.084

MoreBeer:
20 Brix = 1.083 (which is 1.08298 rounded to 3 decimal places). However, it doesn't account for temperature compensation.

Northern Brewer:
20 Brix = 1.083 (which is 1.08298 rounded to 3 decimal places). However, it doesn't account for temperature compensation.

Onebeer.net
20 Brix = 1.08386270136. However, it doesn't account for temperature compensation.

Now look at what I found with a google search "degrees brix to specific gravity"

BellMarketing at 20C:
20 Brix = 1.08297 (no temperature conversion or Brix Correction Factor)

Brewheads.com
20 Brix = 1.083 (no temperature conversion or Brix Correction Factor)

TuxedoParkBrewers.com
20 Brix = 1.0814 (no temperature conversion or Brix Correction Factor)
(This is a homebrew club, not a commercial entity)

GreenwoodAssociates.com
20 Brix = 1.08297 (no temperature conversion or Brix Correction Factor)

Looks like everything is consistent except onebeer.net, BeerSmith, TuxedoParkBrewers, and me. (I am out by 0.00001, and will have to check the rounding in the calculations).
Of course, it is always possible that I am right, and everybody else is wrong, but I doubt it.

-a.