FG target in Brix

[ckirtley]

I use a refractometer, adjusting the FG reading with the Brewers friend calculator. I'm wondering what I should be expecting the FG to be in Brix? My current brew finished at 6 - is that about right?

 

[bradmcm]

More information needed. What was your starting gravity? Is this reading of 6 Brix, the actual reading or after correction?

 

[ckirtley]

1.046 OG (though never quite sure how well mixed the extract was) and 6 uncorrected. I am just trying to understand what the equivalent of, say, 1.01-1.02 is for Brix.

 

[bradmcm]

So 1.046 is 11.4 Brix. Plugging that in to the calculator, your FG is 2.78 or 1.011. meaning 4.7% abv.
In simple terms. the refractometer measures how much sugar is in water. Ethanol affects the refraction when you are measuring it because it is no longer just sugar and water.
That's why you need to use a formula to work out how the ethanol has changed the refraction as the refractomer is reading something it wasn't designed to do.
For example if there was no alcohol - just sugar and water, a reading of 6 Brix is 6 Brix (1.024)
But because there is alcohol in your sample it refracts from 2.78 up to 6.
It's worth getting a cheap hydrometer to double check your gravity after fermentation starts.

 

[raturay]

bradmcm - I'm a little confused with some of the numbers here. I use a spreadsheet to do the conversion from Brix to SG once fermentation has started. It's a spreadsheet my LHB gave me some years ago when I started all grain brewing. It pretty much agrees with your 11.4 Brix being 1.046 SG (within a couple of decimal points). When I plug in 2.78 Brix it results in 0.998 SG. In round figures 1.011 SG comes out at 6 Brix. Most of my brews start around 11.5 Brix say 1.045 SG and finish around 5.5 Brix say 1.008 SG for an ABV of 4.7/8%. Has my spreadsheet been misleading me all this time?
Appreciate your time.

 

[bradmcm]

Your spreadsheet is right but I think you keep switching things around when it comes to true Brix and what your refractometer is reading.

When I plug in 2.78 Brix it results in 0.998 SG

No, you've taken a corrected number and plugged it back in to be calculated again as if it was an uncorrected reading. Go to the Brix conversion calculator Brix Conversion Calculator | Brewer's Friend. 2.78 Brix is actually 1.010 SG.

OK, let's ignore SG units for just a sec and just use Brix.
You have a starting Brix of 11.4. At the end of fermentation your physical reading was 6. Uncorrected. By using the calculator, because we know it started at 11.4, the corrected Brix is 2.8.
Your beer is starting at 11.4 and it is finishing at 2.8 - (11.4-2.8)x0.535=4.8%

Most of my brews start around 11.5 Brix say 1.045 SG

Yes, that's right - 11.5 Brix is ~1.045 SG

finish around 5.5 Brix say 1.008 SG for an ABV of 4.7/8%

No. You are not finishing at this Brix. 5.5 Brix is actually 1.021 SG.
You are finishing where a refractometer says 5.5 uncorrected.
You need to plug that number into your spreadsheet to get the true Brix. Your calculator should show that the corrected, true final gravity is 1.95 Brix which IS 1.008.

I hope this makes more sense.

 

[Coalminer]

Use the calculator at the bottom of Cortez The Killer's First post in this thread

https://aussiehomebrewer.com/threads/refractometer-chart-during-fermentation.17412/
Download link and open in Excel.
plug in the fermentation temp at the top first
I use this all the time = makes life easy

 

[Mooroolbark_Mick]

So 1.046 is 11.4 Brix. Plugging that in to the calculator, your FG is 2.78 or 1.011. meaning 4.7% abv.
In simple terms. the refractometer measures how much sugar is in water. Ethanol affects the refraction when you are measuring it because it is no longer just sugar and water.
That's why you need to use a formula to work out how the ethanol has changed the refraction as the refractomer is reading something it wasn't designed to do.
For example if there was no alcohol - just sugar and water, a reading of 6 Brix is 6 Brix (1.024)
But because there is alcohol in your sample it refracts from 2.78 up to 6.
It's worth getting a cheap hydrometer to double check your gravity after fermentation starts.

Yep, I agree with the hydrometer idea

 

[dmtaylor]

I have put a lot of time into understanding and proper use of refractometers for determining FG. When done right, it is accurate vs. a hydrometer within 0.001-0.002 gravity points.

When FG is expected <1.014, then Sean Terrill's correction calculator is the most accurate. However, change his default Wort Correction Factor (WCF) from 1.04 to 1.00.

http://seanterrill.com/2012/01/06/refractometer-calculator/
When FG is expected >1.014, then use Brewer's Friend correction calculator. This site also tells you how to determine your WCF, and appropriate sets the default to 1.00.

https://www.brewersfriend.com/refractometer-calculator/
In this instance, using Terrill and WCF 1.00 you'll get 1.012. I dare you to measure real specific gravity using a hydrometer. I'll bet a hydrometer is close to the 1.012, in a range of 1.011-1.013.

Brewer's Friend is alright, it calculates 1.011. But I'll bet it's more likely to be 1.012, based on WAY too much of my time spent learning all this stuff.

Also need to make sure you calibrate your refractometer in plain room temperature water with each and every use. Refractometers are a bit touchy and can be inaccurate when used nonchalantly, especially for final post-fermentation readings. If you care about accuracy, do this:

https://www.homebrewersassociation.org/forum/index.php?topic=28544.msg404366#msg404366
Hope this helps somebody. Cheers.

 

[raturay]

Your spreadsheet is right but I think you keep switching things around when it comes to true Brix and what your refractometer is reading.

No, you've taken a corrected number and plugged it back in to be calculated again as if it was an uncorrected reading. Go to the Brix conversion calculator Brix Conversion Calculator | Brewer's Friend. 2.78 Brix is actually 1.010 SG.

OK, let's ignore SG units for just a sec and just use Brix.
You have a starting Brix of 11.4. At the end of fermentation your physical reading was 6. Uncorrected. By using the calculator, because we know it started at 11.4, the corrected Brix is 2.8.
Your beer is starting at 11.4 and it is finishing at 2.8 - (11.4-2.8)x0.535=4.8%


Yes, that's right - 11.5 Brix is ~1.045 SG

No. You are not finishing at this Brix. 5.5 Brix is actually 1.021 SG.
You are finishing where a refractometer says 5.5 uncorrected.
You need to plug that number into your spreadsheet to get the true Brix. Your calculator should show that the corrected, true final gravity is 1.95 Brix which IS 1.008.

I hope this makes more sense.

Thanks, Yeah makes sense. What's interesting is that I'm getting the right outcome in respect to the ABV by sort of reversing the process in my spreadsheet (need to reconfigure that or use one of the other suggested calculators). What we would have called a "buck balance" back in my banking days.