# Hydrometers, Refractometers,Brix, SG & abv. Conversions.



## Becks the Elder (Sep 16, 2009)

*Hydrometers, Refractometers, Brix, SG & abv. Conversions.*

Hi everyone,

I have been using my hydrometer and taking readings and then subtracting the finishing SG from the starting SG and dividing by 7.36 to get the abv.

I have recently been toying with the idea of buying a refractometer so started looking into the Brix scale.

I found an auto conversion webpage:

http://onebeer.net/refractometer.shtml

When I started to put some test calculations through this site I noticed it returned abv figures around 0.6% - 0.7% abv. below those that the subtraction and division method produce. I imagine the webpage results are more accurate as they calculate the figure to about 10 dec. places.

How accurate is the SG subtraction and division method at calculating abv? Would it be more accurate to calculate the abv using the subtraction and division method if the result had a final subtraction of 0.6 applied?

Maybe I've misunderstood something basic somewhere. Can anyone set me straight?

Many Thanks.

Becks.


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## Sacalait (Sep 16, 2009)

Can't help out on the math end since the hydrometer I use has a direct reading of potential alc., brix, and S.G....a triple scale hydrometer. The refractometer conversion table seems to be very close to the direct readings from the hydrometer as well.


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## cpfan (Sep 16, 2009)

Becks:

The division by 7.36 formula produces an alcohol number that is higher than my preferred formula.

(orig sg - final sg) * 133

This formula seems to match closer to the typical triple scale hydrometer.

For example, og 1.100, fg 1.000

1.100 - 1.000 * 133 = 13.3%
1.100 - 1.000 / 7.36 = 13.6%

Some folks use a factor as low as 131

1.100 - 1.000 * 131 = 13.1%

From my perspective, it's 13% wine.

Steve


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## Becks the Elder (Sep 16, 2009)

Thanks guys.

The system you suggested sure makes a lot more sense of the figures I got this morning, Steve.

Many thanks for clearing that up for me. Much obliged.


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## Luc (Sep 16, 2009)

This is going to be complicated. I was planning to do a web-log entry on this but here we go I will spoil the fun a bit.

The formula's you are using are up to discussion.

Look at it this way. Both formula's are the same..........
Huh ??? Well that is easy.

You use OG-GF / 7.36
or OG -FG x 133

Now lets's analyse.

1 / 133 = 0.0075 looks familiar isn't it ???
1 / 7.36 = 0.135 again familiar........
They are eachothers reciproke as called in maths. Inverse in normal language.

So who is right the one that takes 133 (being 7,5) as a figure
or the one that takes 7.36 (being 135) as a figure.

Where do these figures come from.
Well here it starts being complicated.

18 gram sugar makes 1% alcohol
in SG value that is : 18 / 2.6 = 6.92
Now if you presume 19 gram sugar makes 1% alcohol then
the SG vaule would be 19 / 2.6 = 7.3. Now that sounds familiar doesn't it......
And which one is right.....
Some yeast manufacturers say that 16 gram sugar make 1% alcohol (go ahead look it up and look at their webistes.) that would give an even further off figure: 16 / 2.6 = 6.15 in stead of 7.36 !!!!!!!

So the formula is based on the presumption that 19 gram sugar makes 1% alcohol.
So if that presumption is wrong the formula is wrong.

How about the 133 figure.

Well actually in europe we measure SG in whole figures
like 1000 or 1080 or 1050. Not the decimal variation like 1.050.
That actually makes sense as 1 liter water = 1000 ml and weighs 1 kilo or 1000 gram. Whole figures.......

Now if the SG is 1050 we say the sugar is 50 x 2.6 gram (as each point gravity equals 2.6 gram sugar)

Now look at that figure 2.6
And look at the figure in the equation 133.
There you are: 1.33 x 2 = 2.6 (about)

So what ????

Well if we presume that 50% of the sugar is transformed into alcohol then you will have to divide the SG points into 2.
So the 2.6 figure has to be divided into 2 and there is the 1.3 (about)
and as you are working with 1.000 figures you will have to multiply this 1.33 by 100 to get into the whole figure SG range...... There is becomes 133

Now if you are in the other camp that says that the sugar is not perfectly divided in alcohol and CO2 then the figure of 1.3 will likely be 1.33 or 1.31 or any variation on that......even the 135 figure !!!!

So in short.
The figures 7.36 and 133 are quite arbitrary.
it depends on how much sugar YOU thing the yeast need to make 1% alcohol from. And it depends if you presume that 1 point gravity equals 2.6 gram sugar.
So there are 2 variables that at the same time play a part in the formula and both are presumptions.
Meaning that none would be the right one.......

My web-log article will give you more details and samples in calculations. But that will take some time before being published I got first 5 apple wines coming up......

Luc


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## smurfe (Sep 16, 2009)

Thank God Luc chimed in here. He was who I was hoping for as I know he has discussed this before. He saved me a whole lot of typing!


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## Becks the Elder (Sep 16, 2009)

That's all very interesting, Luc. I look forward to reading your full expanded blog version. Thanks for the sneak preview. 

Good Luck with the apple wine.

Becks.


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## saskerrtoon-wine (Jan 4, 2010)

cpfan said:


> Becks:
> 
> The division by 7.36 formula produces an alcohol number that is higher than my preferred formula.
> 
> ...




had some trouble figuring out how to get my alcohol content till i came across this so not sure if i did this right ? This is my first time making wine thanks for all the help everyone..

started out at 1.124-.91/7.36=29% can anyone tell me if i did this right this is from a saskatoon wine i did up this is it at 6 month old PH 3.59 i was very worried when my hydrometer said -2 lol i have no idea what this meant thought i had mad some really good juice


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## cpfan (Jan 4, 2010)

Well 1.124 is a very high initial reading. And .91 is an impossible final reading.

Probably the final reading is .991. If the initial reading is true, then 1.124 - .991 = .133 / 7.36 = 18.07%. Definitely a possible result, although higher than most of use would be trying for.

Steve


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## surlees (Jan 4, 2010)

Saskerrtoon,
Your calculation is right, but I suspect something else is wrong. I doubt your fermentation would have ever gone to .91 if you really started it at 1.124. The yeast would have been killed off well before you got to 29% ABV. If possible, recheck your s.g. readings.

Fred


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## rawlus (Jan 4, 2010)

saskerrtoon-wine said:


> had some trouble figuring out how to get my alcohol content till i came across this so not sure if i did this right ? This is my first time making wine thanks for all the help everyone..
> 
> started out at 1.124-.91/7.36=29% can anyone tell me if i did this right this is from a saskatoon wine i did up this is it at 6 month old PH 3.59 i was very worried when my hydrometer said -2 lol i have no idea what this meant thought i had mad some really good juice



did you use a champagne yeast to drive the alcohol content up to 18%+? i've never personally used seriviceberries but i have read that 16-18% is possible with this juice from simmered fruit. im guessing you added a good deal of additional sugar to the recipe as well.

for calculators, im pretty lazy, i use the online calculators at
http://www.grapestompers.com/calculations.asp
and
http://www.fermsoft.com/products.html


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## rawlus (Jan 4, 2010)

i'd also like to put in a plug for narrow-range hydrometers. for my old eyes, it makes reading down to even 3 decimal places very easy compared to a triple-gauge hydrometer.


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## Manimal (Jan 4, 2010)

The only way to get an accurate measurement of the alcohol content is through ebullimometry or distillation which involve somewhat pricey equipment and a little bit of lab experience. There are too many factors during fermentation that can alter the actual conversion of sugar to alcohol for any arbitrary formula to be very accurate. Different yeast strains, fermentation temperatures, etc. can affect the conversion rate or lead to the volatization of alcohol during fermentation.

That being said, how accurate do you really need to be? Even commercial wineries are usually allowed a +/- 1% deviation on the label in regards to alcohol content (depending on the region of origin and if/where it is being exported.)

Alot of commercial winemakers use a conversion rate of 57% of the starting Brix to get an idea of what the final alcohol content will be. This is an average of the various systems used to determine sugar to alcohol conversion and as such, sometimes the real results will be lower, othertimes higher. But it's a good approximation provided the wine ferments to dryness. 
Eg. 22 Brix X 0.57 = P.A. of 12.54% alc./vol


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## JerryF (Mar 21, 2013)

*Searching for ABV and Using the Brix Scale conversions*



rawlus said:


> i'd also like to put in a plug for narrow-range hydrometers. for my old eyes, it makes reading down to even 3 decimal places very easy compared to a triple-gauge hydrometer.


 
i recognize this is an old post but I just happened on it while searching for information on how to use the brix scales to get to a certain ABV. I too would be interested in a narrow range hydrometer but I've never seen one nor where I would even start looking for one. Jerry


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## JDC (Mar 21, 2013)

http://www.eckraus.com/precision-finished-hydrometr.html

http://home-brewing.northernbrewer.com/brewbeer/Finishing-Hydrometer


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## Runningwolf (Mar 21, 2013)

Presque Isle Wine Cellars has the narrow range brix hydrometers and they're very reasonable.


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## applelover12 (Feb 10, 2016)

Hi Luc
You made apple wine. Do you still do? 
Whats your recipe and what alcohol do you get?





Luc said:


> This is going to be complicated. I was planning to do a web-log entry on this but here we go I will spoil the fun a bit.
> 
> The formula's you are using are up to discussion.
> 
> ...


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