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Question about gotmead calc and ABV%

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AlphaGenetics

NewBee
Registered Member
Jun 24, 2012
25
1
0
Ottawa, ON
Hey all,

I want to ask how I should interpret the calculators output. I'm trying to start up a low % mead for quicker turnaround/ease of drinking. I set up the mead calculator with the following parameters: 20oC temp, 4L volume, and I enter in "target ABV%" of 8%, which kicks out a target SG of about 1.058, corresponding to about 0.8 kg of honey. Now.. I was under the impression mead finishes at 0.990, but looking at the ABV/Brix/SG chart, aiming for 0.8 kg honey/SG of 1.058 would only be around 8% if the mead finishes at 1.000. According to my hydrometer, going from 1.058 to 0.99 would be more in the range of 11%.

Is the calculator (slightly) misleading me?
 
The calculator assumes your mead will finish at 1.000. Chances are really good that it won't, but you can adjust accordingly. For example, if you think yours will bottom out around 0.990, just knock off that extra 10 points from the OG. For folks who use a lot of honey and it ends sweet, the calculator is still going to spit out what happens at FG = 1.000. Again, just adjust for the actual FG.

The calculator is just a guide, not a guarantee. You'll have to tweak the numbers to match your actual situation.
 
Definitely crazy. Welcome to the club. ;D

I assume everything finishes at 1.000, I assume any reading below that is because the ethanol is affecting the specific gravity, and I don't think our calculations correct for that. I suspect that because of this, our alcohol content calculations tend to overestimate the true alcohol content... but until I get a fine scale hydrometer, my alternate method of determining alcohol content isn't accurate enough to put numbers to the theory.
 
Chevette Girl said:
Definitely crazy. Welcome to the club. ;D

I assume everything finishes at 1.000, I assume any reading below that is because the ethanol is affecting the specific gravity, and I don't think our calculations correct for that. I suspect that because of this, our alcohol content calculations tend to overestimate the true alcohol content... but until I get a fine scale hydrometer, my alternate method of determining alcohol content isn't accurate enough to put numbers to the theory.
Click to expand...

I think you may be right. It makes sense; ethanol is less dense than water, so the alcohol you brew must be doing something. I dug around and found this site which is useful for explaining it, and has a little formula at the bottom. Or you could check out this chart to get an idea how much gravity lowers with given alcohol percentages.

Still, I'm sure in reality it's much more complex, what with all the other ingredients, yeast, and byproducts floating around..
 
AlphaGenetics said:
Still, I'm sure in reality it's much more complex, what with all the other ingredients, yeast, and byproducts floating around..
Click to expand...

I'm pretty sure that only soluble components matter, yeast and any other suspended solids won't have any effect. But thanks for posting that info, glad to know I'm not alone in my theoretical suspicions! I'm OK with there being an error to my alcohol percentage calculations, but I do kind of like to know the magnitude of the error, but you can't just slap a streaight "you will be overestimating by X percent" because that amount will differ based on the amount of alcohol... and of course the engineer in me sees the solution being an iterative calculation because the amount of ethanol we're trying to calculate is based on the change in specific gravity, which is going to be affected by... the amount of ethanol produced... lather, rinse, repeat until the amounts stop changing... which makes my lazy brain hurt, so I'm happy to say "within a couple percent!" Although I may well change my bottle labels to say "less than X%" instead of "approximately X%"... definitely easier than doing the math or a spirit indication test for each batch.
 
I don't know if this formula works for mead, but to figure out my beer ABV I do ((((OG - FG)1.05)/FG)/.79) = ABV%

So my cherry vanilla stout was
OG: 1.050
FG: 1.012

So...
1.050 - 1.013 = 0.037
0.037 * 1.05 = 0.03885
0.03885/1.013 = 0.03835143
0.03835143/0.79 = 0.04854612

Or 4.9% ABV

Again, I don't know if that works for mead, I just know I get to play will numbers ^_^
 
It's the same basic idea. The 1.05 factor does vary a bit with total alcohol concentration, so it's not really a constant. It will be close, but not exact. However, the other equations out there are also just close, not exact. Unless you care to be more accurate than about +/- 0.5%, it's close enough. :)
 
The ethanol concentrate will throw off the gravity readings after fermentation has started for determining alcohol content. I use my original gravity and residual sugar tests to estimate where my ABV came it at.

For example, a starting gravity of 1.106 gives me a alcohol potential of 14.1% if all of the fermentable sugars are consumed. Lets say I take a residual sugar test after fermentation has completed and it comes in at 0.8%. That's 0.8 brix or around 1.003 SG. If I revise my original gravity down my 3 points to 1.103, my estimated ABV is now 13.7%

I've found that my meads rarely go dry, even if that's my goal. I started a thread about it here in the patron's section. So far, 0.5% to 1.0% residual sugar is were I end up at. What that means to me, is that my ABV will typically come in below the potential ABV by 0.3% to 0.6%. Unless I can figure out how to make a truly dry mead.

If you plan to back sweeten, then you'd need to calculate in the dilutive effect of that if you really wanted an accurate estimate at ABV.
 
Thanks for the excellent discussion. Long story short then, it is complicated. Without going to the trouble of getting residual sugar tests my best bet is to assume the calculator is correct. In reality, any sugar I begin with is adding on to the 1.000 of water. Even if by the end of fermentation if it drops below that, it's not like sugars have be invented out of thin air. I'll just rely on stable readings over a few days, somewhere between 0.990 and 1.000, to know when to quit.
 
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