ABV % Confusion of the highest order!

[Kemsley]

I understand what Specific Gravity is and how to take my readings and found calculators to work out my ABV. I mixed my Juice, Water and Honey together and in the case of my Apple Mead the result was an initial SG of 1166 (A little high I know) and after the fermentation seemed to have run its course (EC118 yeast) I took a second reading at 1062 both adjusted for temperature according to the chart that came with my hydrometer. So far so good but when I put my results into an online calculator (Im using Brewers Friend but have similar issues elsewhere) I had a disappointing 13.65% Alcohol but I noticed a setting marked "Alternate equation" which when clicked gives a more reasonable 17.38%. My question is which is correct? After watching a few you tube videos and reading abit there seems to be a lot of confusion about exactly how to calculate this with alot of debate on the topic. This makes me more confused because surely all debate could be settled immediately by using Gas Chromatography to check the result proving which calculations are actually accurate and I feel like someone somewhere must have done this. How can I know the ABV if there are multiple ways to calculate that have such dramatically different results?

I intend to pasteurise my mead before sealing it with a stopper for aging, I was just wondering if a cork stopper in a Demijohn will be safe for 1year aging as I'm not sure cork is 100% airtight.

 

[mac_1103]

Scroll down and read the fine print:

"This calculator allows you to choose between the standard equation or the alternate equation. If you don't know the difference, just stick with the standard equation. Read more about this update here."

Click on the link to read more. The alternate equation is supposed to be more accurate at higher gravities, but I've never used it and I have no idea how high is higher.

 

[Kemsley]

Thanks for the reply, I had read this and it just made me even more confused. There can only be one true answer and when I have found videos or articles of people talking about this they seem just as confused as me. Is my mead 13% or 17%! How can there be two accepted formulas that yield such varied results, its not magical its science there must be a definitive way to calculate this.

What makes me even more baffled is there are actual scientific ways to test these results so surely people have figured out what formulas are actually accurate by just testing in a lab? Someone must have done this.

 

[mac_1103]

Ethanol lowers specific gravity since it is less dense than water. The standard ABV formula does not account for this; it estimates how much ethanol was produced based on the difference in sugar content pre- and post-fermentaion. So at higher ABV the simple formula starts to break down.

 

[Kemsley]

If thats the case why does the alternative calculation make the % go up? If the gravity should be lower because of the presence of a higher concentration of alcohol why does taking that into account raise my % by 4?

 

[Raptor99]

It's more complicated than that. The ABV calculators give us only an approximate ABV, based on certain assumptions. The SG does not directly measure sugar content. Anything dissolved in the mead will increase the SG, and ethanol will lower it. There is not a simple formula that will give you a 100% accurate ABV number.

The calculators based on formulas that attempt to approximate the relationship between the change in OG and ABV. They are all approximations, and all are less accurate in certain ranges.

I don't know anything about the "alternative calculation" that you found, but you could do some research into different ABV calculators to understand the assumptions and limitations of each. In any case, they all will provide only an approximate ABV. To measure it directly, as you say, you would need to use something like gas chromatography.

In addition to the link shared above by @mac_1103, you could read this: ABV Calculation Different to Other Calculators

 

[Rish]

I don't really worry about what the abv is. I just make it and drink it.

 

[mac_1103]

I don't really worry about what the abv is. I just make it and drink it.

Sometimes I start to worry about it after I drink it...

 

[IslandLizard]

I don't really worry about what the abv is. I just make it and drink it.

Many (most?) homebrewers don't seem to care about ABV, they're concentrating on best flavor, aroma, appearance, clarity, balance, how it compares to other beverages they've brewed and drank, commercial examples, etc.

Now some (other) individuals seem to be obsessed with alcohol percentage... and not much else...

 

[sampling6391]

I use SG readings to measure so I can try to get close to the target OG and to tell when fermentation is complete by taking readings after airlock activity stops.

I use the (OG - FG) X 131.25 = ABV calculation for my brews mostly for the giggles. I figure a $10 hydrometer and my bad eyesight isn’t going to be nearly enough to get a scientifically accurate ABV anyway.

Also make sure you’re compensating for any temperature difference if you’re measuring your brew hotter or colder than your instruments are calibrated for.

 

[AZ Maverick]

Personally, I use the alternate method for all of my brews.
The simple method is easy to remember and easy on the math, but as already stated it starts to deviate from actual ABV as the alcohol level increases.
The alternate method is more difficult math to remember, but imo, it's the more accurate formula regardless of the ABV so that's what I use for everything (my computer does all the math anyway).
Short of a mass spectrometer reading , these formulas are about as close as you can estimate.