Tool to measure abv?

[VikeMan]

i just looked at your post #59 and #70.....read this but as the refractometer goes down due to less alcohol...the hydrometer goes up, thus comparing the two and using the calc works? because as the refrac goes down, the hydro goes up?

No, because both formulae still contain the underlying assumption that any alcohol created was made from a specific reduction in extract. If you try to use them in the opposite opposite direction, they have to assume that any alcohol removed was replaced by a specific amount of extract, because the relationship has to hold regardless of whether you are adding or subtracting alcohol. The fact that one of the formula's uncorrected reading goes up and the other formula's uncorrected reading goes down doesn't somehow fix the two broken formulae: broken in the sense that they can't be applied to solving what we're trying to solve.

I believe there is (maybe) a formula that would work. It just hasn't been written yet.

 

[DuncB]

Normally the mere mention of the word Barbecue was enough to bring on weather that prevented outdoor catering.
Apparently hottest day in March in london on record today. But not barbecue weather by law not conditions.

 

[bracconiere]

I believe there is (maybe) a formula that would work. It just hasn't been written yet.

well man, i just did a second test with the one built into beersmith....i added 23 grams of 65% ABV, so 52% by weight of brandy to a graduated cylinder....added 275 grams of water to it...for around 298 grams total which would equal about 4% by weight theanol, i added some sugar, enough to where the hydro was above 0...


i got 1.006 on the hydro and 5 brix on the refrac, beersmith told me pretty much spot on it had 3.82% alcohol by weight.....and being i lost a few grams shaking it with my hand cupped on it.....i think it works.....

\edit: and honestly, i made this brandy a long time ago...and it might have been 62-63% ABV which would work out to exactly 3.82% by weight ethanol.....

 

[1979doc]

Beer refractometer with some interesting articles at the end of the page.
https://www.misco.com/refractometer-applications/food-beverage-refractometer/beer-refractometer/

 

[Birrofilo]

Beer refractometer with some interesting articles at the end of the page.
https://www.misco.com/refractometer-applications/food-beverage-refractometer/beer-refractometer/

Talking about the refractometer, frankly, this seems a huge price to pay for a refractometer that cannot offer anything really justifying the cost.

Although they use a lot of marketing bullstuff, what this instrument provides in addition to a normal instrument is:

a) An incorporated correction factor which, rather than being fixed (such that 1,04) is "something else", of which we know nothing. It probably consists in a function, for instance the correction factor increases with the density of the sample.

b) Using some corundum instead of glass and maybe a larger sensor to read the light beam;

The result is that, "on samples from a dozen different worts" (really an impressive and independent lab test ) the density error was 1 density point or less. Normally one would get that kind of precision with a normal €40 refractometer, maybe 2 density points of error, but if you test your refractometer with 12 worts of your choice, I am sure you will get 1 density point maximum error.

I am not impressed.

The document though hints, if I read it correctly, at the correction factor being higher with a higher density, which could be useful information.

 

[mattrix]

OK I know this thread is 2 years old, but I think my questions fit here.
I'm a bit lost.

Assuming the unfermented mix is just dextrose and water, because I don't know how all the other stuff affects a hydrometer.

If the brew is fermented to absolutely dry, isn't the SG related to the alcohol content? And as the alcohol is removed the SG will approach 1.000?

No-one seems to have mentioned this.


Secondly, people keep saying that given OG and FG, they know the dextrose consumed.
The OG sample is dextrose and water, so any deviation from 1.000 is due to the dextrose.
However the FG sample is water, dextrose and alcohol,.
As dextrose is consumed the SG reduces,
As the alcohol increases the SG reduces
What correction is used on FG to get the dextrose component?

I thought this would be solvable by rearranging the equations, but I came up with problems calculating the volumes.
* If I add 50mL of alcohol to 950mL of water is the final volume necessarily 1000mL? I think not, surely some of the alcohol will interact with the water and not increase the volume.
*If I add 50g dextrose to 950mL water and the resulting volume is 965mL, if I then add another 50g dextrose will the final volume necessarily be 980mL? I think the volume will increase more per gram added when the concentration is higher.

 

[VikeMan]

Assuming the unfermented mix is just dextrose and water, because I don't know how all the other stuff affects a hydrometer.

If the brew is fermented to absolutely dry, isn't the SG related to the alcohol content? And as the alcohol is removed the SG will approach 1.000?

If by "brew" you mean your fermented dextrose and water solution, then yes, if you removed the alcohol, then the SG would be 1.000 (ignoring "insignificant" fermentation products that are also in solution). (Real beer will never be absolutely dry, because of unfermentable dextrins.)

Secondly, people keep saying that given OG and FG, they know the dextrose consumed.
The OG sample is dextrose and water, so any deviation from 1.000 is due to the dextrose.
However the FG sample is water, dextrose and alcohol,.
As dextrose is consumed the SG reduces,
As the alcohol increases the SG reduces
What correction is used on FG to get the dextrose component?

Given OG and FG, they do not know (precisely) the dextrose (or other sugars) consumed. They use a formula such as the following, which gives an approximate ABV.

ABV = (OG - FG) * 131.25

The correction you're seeking is baked into the 131.25 "constant." But it's not a well defined number, because it's actually different for different beers. Different values for the constant (and more complex formulae) can be useful over different ABV ranges, but at the end of the day, it's still always an estimate.

When gravity decreases, it's because some amount of sugars have been consumed, turning into some amount of alcohol and some amount of CO2 (most of which escapes). The proportions of alcohol and CO2 produced are roughly 50/50, but this varies (and also ignores small amounts of other products).

* If I add 50mL of alcohol to 950mL of water is the final volume necessarily 1000mL? I think not, surely some of the alcohol will interact with the water and not increase the volume.

You are correct. The final volume will be something less than 1000 ml.

 

[rushpapers]

Vernier makes an ethanol vapor sensor. It does not give exact abv, but can be used as a tool to measure fermentation.

 

[bracconiere]

You are correct. The final volume will be something less than 1000 ml.

wait? wouldn't the weight just not be 1000g's?

water is 1g/ml

ethanol is .789g/ml....


so i think, correct me if i'm wrong, adding 50ml to 950ml water, will indeed give you a 'volume' of 1000ml, but it will only weight ~989g's, which you can figure both ABV and ABW from....

 

[VikeMan]

so i think, correct me if i'm wrong, adding 50ml to 950ml water, will indeed give you a 'volume' of 1000ml, but it will only weight ~989g's, which you can figure both ABV and ABW from....

Water Volume + Ethanol Volume > Combined Volume

https://www.thoughtco.com/miscibili...:text=If you add 50 mL,of liquid, not 100 mL.
https://www.ethimex.com/blog/2022/07/19/what-you-need-to-know-about-ethanol-shrinkage/
You can think of it in terms of miscibility (first link) or in terms of hydrogen bonds (second link), but both are essentially different views of the same phenomenon.

 

[bracconiere]

Water Volume + Ethanol Volume > Combined Volume

https://www.thoughtco.com/miscibili...:text=If you add 50 mL,of liquid, not 100 mL.
https://www.ethimex.com/blog/2022/07/19/what-you-need-to-know-about-ethanol-shrinkage/
You can think of it in terms of miscibility (first link) or in terms of hydrogen bonds (second link), but both are essentially different views of the same phenomenon.

well i read both those, i liked the first one for toddlers the best with the line "sand mixed into gravel".... thanks for both of them!


(of course i just looked up the mol weight and ethanol is actually the gravel? and not smaller?)

 

[VikeMan]

(of course i just looked up the mol weight and ethanol is actually the gravel? and not smaller?)

Yes. Good catch. The explanation in the link is good, but she flipped-flopped her molecules.

 

[bobtheUKbrewer2]

1 litre of a 4% ethanol solution weighs 998.93 grams, 1 litre of a 1% ethanol solution weighs 999.73 grams. It is a linear relationship so easy to calculate 5%, 6% etc. So weigh a volume V of your beer, reduce its alcohol, and weigh the same volume to determine the new % alcohol. Pretty accurate scales are needed though. I would see how many pints I could drink of the reduced alcohol beer before falling over to estimate its strength.........

 

[mattrix]

Given OG and FG, they do not know (precisely) the dextrose (or other sugars) consumed. They use a formula such as the following, which gives an approximate ABV.

ABV = (OG - FG) * 131.25

The correction you're seeking is baked into the 131.25 "constant."

Thank you for that explanation.
And for your later links, It is always nice to have an explanation for one's gut feeling.

I can see my solution for the OP was a bit too simplistic.

1 litre of a 4% ethanol solution weighs 998.93 grams, 1 litre of a 1% ethanol solution weighs 999.73 grams. It is a linear relationship so easy to calculate 5%, 6% etc.

Hey Bob, where did you get your figures from?
I used this site , but their figures don't agree with yours; and theirs are definitely not linear when plotted 'solution weight per litre' against '%ABV' or 'weight of ethanol'


Edit. Actually I think your figures are based on water with 1000g/Litre (4'C?), mine are at 20'C
But I don't think this will change the linearity??

Edit 2: I may be misinterpreting this, or my references; I keep thinking of things I havent considered. Please point it out if I have.

 

[beren]

Given OG and FG, they do not know (precisely) the dextrose (or other sugars) consumed. They use a formula such as the following, which gives an approximate ABV.

ABV = (OG - FG) * 131.25

There’s a newer more complicated formula but a lower abv it’s almost the same as this one. Some online calculators allow you to pick this. If you want a true reading take it to a lab with a mass spectrometer but it might cost $200-300 for the test

 

[VikeMan]

If you want a true reading take it to a lab with a mass spectrometer but it might cost $200-300 for the test

About 30 bucks, and accurate enough for the TTB:
https://www.whitelabs.com/lab-services-product-detail?id=20&type=PRODUCT

 

[bobtheUKbrewer2]

Mattrix - I just looked up the density of ethanol, and deduced the volume of 1 gram of ethanol. It is clearly less then 1.000. I was being a bit tongue in cheek as the required weighing accuracy scuppers it. Having said that, 67 years ago I was taught to calculate density of a liquid using a small glass jar, and a stopper with a tiny hole in it. You filled it to the brim, inserted the stopper which displaced excess liquid, then weighed it.

 

[mattrix]

... I was being a bit tongue in cheek as the required weighing accuracy scuppers it ...

Oops, I missed that.
My "math" brain took over. It knows nothing about practicality.

 

[bracconiere]

i'd want to add this again...there is the differential between refractive index and SG to get a very close guess..


honestly it might have been this thread or similar, that inspired me to get a refrac to do just that....

 

[bobtheUKbrewer2]

I was starting with ABW of course.......

 

[DuncB]

i'd want to add this again...there is the differential between refractive index and SG to get a very close guess..


honestly it might have been this thread or similar, that inspired me to get a refrac to do just that....

I think that @VikeMan explained that in another thread but I can't track it down.

 

[bracconiere]

I think that @VikeMan explained that in another thread but I can't track it down.

and here i thought it was explained a lot in the past, with high FGs? (where i learned it)

 

[cheech226]

i've had people taste my mead and ask about the apv. the only % i can tell them is read on the % alcohol line (next to the sg line) on my hydrometer, if i ferment to 1.000. assuming honey only mead, how close to reality is that number? generally? tia

 

[mattrix]

... if i ferment to 1.000. assuming honey only mead, how close to reality is that number?

I'm not sure, but since no one else has responded, I'll throw in my 2c worth,
Before the ferment, the alcohol value on the hydrometer assumes only sugar and water, and that all of the sugar is fermented.
What is left, alcohol and water, would have a SG less than 1.000

So if the ferment ends at 1.000, some of the sugar, or whatever, is left unfermented.

So the actual alcohol will be somewhat less than the original SG suggests.

 

[bracconiere]

So if the ferment ends at 1.000, some of the sugar, or whatever, is left unfermented.

might have to add instead of subtract, if it goes to something like .995

 

[mac_1103]

So if the ferment ends at 1.000, some of the sugar, or whatever, is left unfermented.

Yes, if you fermented a sugar wash. But not if you fermented "whatever." Honey is not pure sugar and is not 100% fermentable.