Tool to measure abv?

[Birrofilo]

Before I get too tired (it's 3:25 here) I have an idea which might be interesting for the OP.

IF your process is clearly repeatable, you could:

a) Make 10 samples of 10 different degrees of alcohol reduction;
b) Make accurate measuring of whatever parameter you find differentiating enough: refraction index with a refractometer, gravity with a hydrometer in the proper density range, or anything else like weight (with one of those scales that go to the 1000th of gram and that actually work), colour, whatever you have an instrument for.
c) Give those 10 samples to a laboratory for a serious and precise alcohol content response using the most precise method they can;
d) Make a table of the 10 ABV values the laboratory gave you and the 10 values that you observed at home.

If they make a nice curve, or even better a nice line on a graph, then you don't need to send any more sample to the lab.

For each beer you make, you can measure your own value and relate it to the table.

The problem here is "repeatability" of course. You could postpone this until you have a recipe that you can brew with good uniformity, and a measuring method that you have nailed down with sufficient accuracy.

If a hydrometer or a refractometer differentiate enough your samples at different ABV, you can pay the lab only once.

 

[RufusBrewer]

Ultimately unless you're incredibly accurate in your volume reading of your distillate, which if I understand correctly is the most critical error point, how you accurately measure the density thereafter depends on that first accuracy anyway. The method I saw derived ABW from the weight of distillate and then calculated ABV from there.

I haven't had a chance to try it hands on yet but it's on my to do list.

Wouldn't accurate measurement of the starting volume be critical as well. You could measure X grams of distillate or Y liters of distillate, dead nuts accurate. It would be of marginal value unless you knew you drew that from Z liters of beer with an X.Y% ABV.

 

[bracconiere]

i thought the refractometer reading compared to a hydrometer reading was good enough? now i'm wondering?

damn, at this point i need proof....i'm going to order a refractometer off ebay, and try it out on a batch...see if the calcs work....

well, i got my refractometer. and i've been f'n around with it comparing it to hydrometer readings...so far the calcs all work....i tested a known batch of beer, whiskey and water.....the calcs co-incide with my measurements for how much ABV they have.....handy trick


as an update to the thread...

 

[rushpapers]

Just take a second FG reading after de-alcoholizing and calculate the % drop.

What's the problem?

 

[DuncB]

Send a sample in a blood tube to the local blood lab and they will tell you the alcohol amount in mg/ litre.

 

[rushpapers]

If you don't have an OG it's a problem

If you do have OG it is pretty damn simple.

A refractometer measures brix of a liquid based on how light bends or the "refraction" through a liquid.

Hydrometer measures the density of liquids.

 

[Vale71]

OK I'll bite.

OG: 12°Brix
FG before ethanol removal: 8.5°Brix
FG after ethanol removal: 6°Brix

What is the ABV after alcohol removal?

 

[VikeMan]

Just take a second FG reading after de-alcoholizing and calculate the % drop.

What's the problem?

What formula do you propose to do this? You can use the data in post #47 as an example if you don't mind.

 

[Smiling Frog]

OK I'll bite.

OG: 12°Brix
FG before ethanol removal: 8.5°Brix
FG after ethanol removal: 6°Brix

What is the ABV after alcohol removal?

Where did you get these numbers?

Assuming none of the dissolved solids are removed when the alcohol is removed (that is, only alcohol and water is removed), the SG should go up, not down. If you are getting a lower SG after you removed the alcohol, you have removed a lot of the dissolved solids (roughly, 21% of the remaining sugars : 1.5/8.5= 0.21)

 

[bracconiere]

OK I'll bite.

OG: 12°Brix
FG before ethanol removal: 8.5°Brix
FG after ethanol removal: 6°Brix

What is the ABV after alcohol removal?

i just punched 6 brix and a guess at what a hydrometer reading would be of 1.019...(assuming a bit higher with alcohol removed)


and i get 1.6%ABV

 

[rushpapers]

The example given is incorrect, it's like saying your gas tank will have more fuel after driving 300 miles.

It would be like this.

OG: 1.060/14 Brix
FG: 1.010/2.6 Brix

ABV 6.67%

New FG after de-alcoholizing: 1.030 7.6 Brix

New ABV 4.0%

 

[Vale71]

Except ethanol will actually cause a refractometer reading to increase compared to the actual value, which is why you need a correction formula.

It follows that if you were to remove ethanol from the mixture the refactometer reading would actually decrease but if you were to apply the same correction formula you would get a false, higher calculated ABV value.

See, it's not as simple as you think. Unless you have no idea about how something actually works, then everything is easy-peasy...

 

[Vale71]

Where did you get these numbers?

Assuming none of the dissolved solids are removed when the alcohol is removed (that is, only alcohol and water is removed), the SG should go up, not down. If you are getting a lower SG after you removed the alcohol, you have removed a lot of the dissolved solids (roughly, 21% of the remaining sugars : 1.5/8.5= 0.21)

See previous post.

 

[VikeMan]

Except ethanol will actually cause a refractometer reading to increase compared to the actual value, which is why you need a correction formula.

It follows that if you were to remove ethanol from the mixture the refactometer reading would actually decrease but if you were to apply the same correction formula you would get a false, higher calculated ABV value.

This is the correct answer. Since it has now been mentioned in various ways at least 3 times in this thread, perhaps it will stick.

 

[rushpapers]

Yes it is that easy.

Use a hydrometer. I never said use a refractometer.

If you take away alcohol (ethanol, isopropyl, etc.) from the solution of beer, and nothing else, the beer will become more dense.

It's simple high school chemistry.

 

[Vale71]

That's what was being discussed so it was natural to assume you were talking about refractometer readings as well.

Even with a hydrometer it's not that easy. If you hold your beer at those temperatures for quite some time there will be some water evaporating as well and that will affect the outcome. Unless you want to start calculating differential water/ethanol evaporation rates the accuracy of the calculated value will suffer.

Then there's all that wasted beer if you have to take repeated measurements to determine when a certain ABV threshold has been crossed. If only actual densitometers weren't that expensive...

 

[Birrofilo]

If you take away alcohol (ethanol, isopropyl, etc.) from the solution of beer, and nothing else, the beer will become more dense.

A hydrometer only tells you density. Alcohol content is always the result of a calculation which is possible only because of the fixed relation between the gravity (sugar) that is missing and the alcohol which is produced when that quantity of missing sugar is consumed.

We estimate alcohol because we measure OG, subtract FG, which means we know how much sugar was converted into alcohol and CO2. It's only the missing sugar which tells us the alcohol in the liquid, not the density.

To make an extreme example, a hydrometer can tell you the density is 1,012 and this could be a final gravity (alcohol present) or an original gravity (no alcohol present). The hydrometer doesn't know about the fermentation and cannot be used to evaluate alcohol.

If you use the new FG after de-alcoholizing and compare that with the original OG, you don't have any more a correct relationship between OG and FG that can give you the sugar missing, hence the alcohol in the beer.

This is a problem which is similar to infering density with a refractometer if alcohol is present.
If you have a mixture with three substances (water, sugar, alcohol) you cannot use a hydrometer or a refractometer to arrive to the direct determination of each substance.

You could do that only if there are two substances in a liquid because in that case you can "draw a table".

 

[rushpapers]

...and we know the effects of sugar and alcohol on the density of liquids. If we have our numbers we can calculate changes.

If you want to bang your heads against the wall, by all means.

You take alcohol away, you then have a new FG to calculate with.

It's that simple.

I could understand this being difficult if the OG was unknown.

And a refractometer would work as well.

 

[VikeMan]

Yes it is that easy.

Use a hydrometer. I never said use a refractometer.

If you take away alcohol (ethanol, isopropyl, etc.) from the solution of beer, and nothing else, the beer will become more dense.

It's simple high school chemistry.

The standard hydrometer ABV formulae rely on an underlying assumption about how much ethanol (which is less dense than water) is made per mass of extract lost. If you remove alcohol without putting the extract back, you've broken the underlying assumption.

 

[VikeMan]

And a refractometer would work as well.

No, as @Vale explained pretty clearly in post #52.

 

[Smiling Frog]

See previous post.

You're previous post only talks about refractometer readings, not specific gravity readings, as quoted in post #47.

 

[rushpapers]

That's why I stated a % calculation.
Measure the volume (weighing) would be more accurate.
Take original % BY VOLUME, and calculate the change.
ABV is % alcohol diluted in beer. As you take it away density changes, but so does volume. Calculate the % loss.

But frankly it's going to be so small it's negligible.

 

[Birrofilo]

...and we know the effects of sugar and alcohol on the density of liquids. If we have our numbers we can calculate changes.

If you want to bang your heads against the wall, by all means.

You take alcohol away, you then have a new FG to calculate with.

It's that simple.

I could understand this being difficult if the OG was unknown.

And a refractometer would work as well.

Man, you should listen, and you don't listen. Stop a moment to think what we are saying.

One of the many formulas to derive alcohol from density is this:

% ABV = [(OGp - FGp) / 7,46]

The reason why the formula uses OG - FG is that it is sugar missing which lets you derive alcohol produced by that sugar.

If you take alcohol away, and your density rises, applying this formula your ABV goes down but that doesn't mean that this formula tells you the actual alcohol present. The (OGp - FGp) part has not any more the same significance, it will not tell you anymore the sugar consumed during the original fermentation.

 

[rushpapers]

No, as @Vale explained pretty clearly in post #52.

 

[Birrofilo]

That's why I stated a % calculation.
Measure the volume (weighing) would be more accurate.
Take original % BY VOLUME, and calculate the change.
ABV is % alcohol diluted in beer. As you take it away density changes, but so does volume. Calculate the % loss.

But frankly it's going to be so small it's negligible.

If the part which is subtracted by beer is collectible, and the relative percentage of alcohol and water is measurable in the subtracted part, then yes I do agree it could be possible to make some equation that calculates the alcohol present in the beer.

But you cannot eliminate alcohol without eliminating water as well if you use heat, therefore you cannot derive the ABV remaining in the kettle if you don't calculate the ABV of the evaporation (the product of the distiller).

But it's not easy method, one cannot simply take the FG and apply the old same formula.

 

[Birrofilo]

[Graph connecting the deviation alcohol creates in a sugar solution density measured by refraction index]

This is actually interesting and, thinking about it, it might be possible to:

a) Measure the density by the hydrometer;
b) Measure the density by the refractometer;
c) Knowing the real density, and observing the deviation between refractomer and hydrometer, one can infer how much alcohol there is because the deviation is due to the alcohol, and the more the deviation, the more the alcohol.

This might be the right solution to the OP problem. Actually I think it really is, and it's not that complicated after all. It will not be extremely precise because there is the old usual imprecision given by the fact that wort is not a real sucrose solution, but it should give a result which is only a few percentage points wrong.

 

[Smiling Frog]

{attachment removed}

rushpapers, where did this graph come from? Is there a way I can get the original paper?

 

[Birrofilo]

rushpapers, where did this graph come from? Is there a way I can get the original paper?

I found it here: EtOH to Brix and Measurement of %ABV

 

[Birrofilo]

The simple method should be:

Get the post-dealcoholization gravity of the beer with a hydrometer. Let's say it is 3,5 °Brix.
Get the post-dealcoholization gravity of the beer with a refractometer. Let's say it is 4,5° Brix.

Draw a line in the graph starting from 3,5 and keeping the line parallel with the other lines in the graph.
Draw an horizontal line in the graph starting from 4,5.
Where the two lines cross, the value on the abscissa gives the ABV in %.

Should be easy-peasy.

 

[VikeMan]

"attachment"

I see the three lines on that graph all have different slopes, which does not support the use of standard refractometer formulae to determine ABV after alcohol removal. How would you determine a slope to use for a particular beer? And even if that were easy, the refractometer ABV formulae wouldn't accommodate that anyway.

When you remove alcohol (and change nothing else), the refractometer reading decreases. Just as it would if some more extract had been removed, along with an increase in alcohol. The refractometer ABV formulae solve for the latter and not the former.

 

[Birrofilo]

The "method" outlined in my post #69 is not correct because the graph tells me the "added" alcohol by the refractometer, not the "added density". Should work more on it. It's possibly the right direction of investigation, though.

 

[Smiling Frog]

This is actually interesting and, thinking about it, it might be possible to:

a) Measure the density by the hydrometer;
b) Measure the density by the refractometer;
c) Knowing the real density, and observing the deviation between refractomer and hydrometer, one can infer how much alcohol there is because the deviation is due to the alcohol, and the more the deviation, the more the alcohol.

This might be the right solution to the OP problem.

This is likely to the way to a better determination of the alcohol content (likely better than the [OG-FG] method). A couple of problems, however. One, in step b), remember that the refractometer does not measure density. You cannot "measure the density by the refractometer."

One of my major complaints about the cheap hand-held Brix refractometers on the market is not that they are of poor quality or that they are not accurate, but they do not give you a reading of the property they are measuring. They measure the refractive index but give you a reading of % sucrose (or even more egregiously, a density reading). While (as best as I can determine) these values are correct when dealing with pure sucrose and water solutions, things change when you get to the real world.

I would change/redefine your method to:

a) Measure the density of the beer with the hydrometer to get an estimate of the % sugars present in the final beer
b) Measure the refractive index of the beer
c) Assuming the two major factors that affect the refractive index of the beer are the sugar content and the alcohol content, if the sugar content is known, the alcohol content should be able to be estimated.

 

[rushpapers]

This is actually interesting and, thinking about it, it might be possible to:

This is what I am looking for. Thanks.
I may not be completely right in my method, but am right that there is a simple method that can be done on paper.

I don't have the time to work it out for you in text, but it's not that hard.

You need to realize these are calculations, laws and constants. You can do this.

You don't need a fancy $2000 tool.

 

[Birrofilo]

This is likely to the way to a better determination of the alcohol content (likely better than the [OG-FG] method). A couple of problems, however. One, in step b), remember that the refractometer does not measure density. You cannot "measure the density by the refractometer."

I know. It should have read as "read the apparent density by the refractometer". The refractometer applies an internal look-up table to convert RI to the density of a syrup.

One of my major complaints about the cheap hand-held Brix refractometers on the market is not that they are of poor quality or that they are not accurate, but they do not give you a reading of the property they are measuring. They measure the refractive index but give you a reading of % sucrose (or even more egregiously, a density reading).

You can determine the RI by using the look-up table in the other direction.

I would change/redefine your method to:

a) Measure the density of the beer with the hydrometer to get an estimate of the % sugars present in the final beer
b) Measure the refractive index of the beer
c) Assuming the two major factors that affect the refractive index of the beer are the sugar content and the alcohol content, if the sugar content is known, the alcohol content should be able to be estimated.

Besides the "recalling" of my method, I think a) has a problem, that the % sugars present in the final beer is not entirely knowable even by a hydrometer reading, because the alcohol present is skewing (lowering) the density thus bringing to an underestimation of the sugar in the beer.

 

[Birrofilo]

I don't have the time to work it out for you in text, but it's not that hard.

You need to realize these are calculations, laws and constants. You can do this.

You don't need a fancy $2000 tool.

I agree it is probably possible to make an equation, but I don't agree that it is easy. This is a problem akin to the estimation of density of a beer with a refractometer with alcohol present. Proper mathematics might require an iterative calculation, or some very complicated equation.

 

[rushpapers]

As the percent alcohol in a solution is reduced, the volume, mass and therefore density will change accordingly. Ethanol has a constant density, which can be calculated into percentage loss.

 

[bracconiere]

well i see i must have been set to ignore....lol


but anyway....i just weighed out a known amount of 65% alcohol, with wood sugar and all in it.....added it to known amount of water....measured it BOTH with a hydrometer, AND refractometer....and the calculator to compare the two was pretty much spot on to what it should be.....


so YES, alcohol increases a refractometer, AND lowers a hydrometer...thus comparing the two, you can calculate ABV....assuming you're not trying to drink acetone or something, as long as it's just water, sugar, and ethanol....(i think anyway, just got my refrac, and having fun with it!)

 

[bobtheUKbrewer2]

Both hydrometers and refractometers are inaccurate for FG readings. But what does it matter ? It is consistently inaccurate. I aim to make 3.8% SMASH beers. Maybe they are REALLY 3.6% or maybe they are REALLY 4.2%. I have my recipe, I have my methodology, I like the end result.

The only way to determine ABV is in an accredited laboratory. In the UK breweries have to have their ABVs calculated accurately once a year. And it is not unknown for breweries to declare lower ABVs to pay less duty but supply beers that are 0.5% higher.

There are more things to worry about than the accuracy of measured ABV for home brewers.

Just get some nice beers brewed (make beer before the sun shines) because barbecue season starts in 21 days in southern UK.

 

[Vale71]

Both hydrometers and refractometers are inaccurate for FG readings. But what does it matter ?

To the OP it matters a lot since he plans to de-alcoholize his beers and needs a way to determine wether he was succesful or not. The fact that you don't care about ABV does not really help him.

 

[bobtheUKbrewer2]

ok - I personally do not know how to remove 100% alcohol, but I do know where to find out how much alcohol is left in the equilibrium solution. Will follow this thread carefully.