actual ABV if ends at .992

[cintipam]

Hi you wonderful techie folks

I do understand how to calculate ABV, but that seems to be based on wine ending at 1.00. I ferment to dry, and often hit .992. Does that mean my wine is slightly higher ABV than if it ferments to 1.00?

Pam in cinti, gently buzzed from taste testing 2 carboys I racked today.

 

[wineforfun]

Yes, that is correct. I don't have my chart in front of me but I believe it adds approx. 1.3%

Or

Initial SG - Final SG x 1.33 = ABV is the general calculation.

 

[cintipam]

Thanks very much. I had no idea how to calculate this when it goes into the negative like that.

I could feel it, but I couldn't prove it.

Pam in cinti

 

[seth8530]

Yes, that is correct. I don't have my chart in front of me but I believe it adds approx. 1.3%

Or

Initial SG - Final SG x 1.33 = ABV is the general calculation.

One thing to be very careful about when writing equations is watching your parentheses or lack there of. Since they can dramatically change the meaning of the equations

SG-FG*1.33 and (SG-FG)*1.33


Using the numbers of SG=1.1 and FG=.990 the first result yields -.2167

and the later yields .1463

( I assume both of these are supposed to be multiplied by 100 to make them percents)

However, one thing to also keep in mind is that their are a very large number of ABV equations.. and I highly doubt any of them is what I would call exact. So just some general things to keep in mind.

But to the original question just use one of the many available ABV equations to get your approximate ABV

Such as (SG-FG)*131

or (SG-FG)/.736

Both of these equations would give you your ABV in %

 

[cintipam]

Seth, incredibly well phrased. I say that cause I pretty much followed your logic. Not that I could have gotten there on my own at all, but with those formulas I can actually figure it on my own now. I had just been counting on the hydrometer SG readings before, but logically when you hit the negative things change.

Thanks so much, and I bow to your skill with numbers.

Pam in cinti

 

[seth8530]

Thanks I am glad it helped.

 

[Tom_S]

I thought that the ABV is whatever your potential alcohol is at the start minus the finished potential alcohol, down to 0%. I always understood that if it goes below 0, that's because of the lesser gravity (and buoyancy) of the alcohol in the finished wine as opposed to the water in the juice at the beginning. That is, the alcohol makes the SG of the wine go below 1.00, but it shouldn't add extra ABV.

 

[wineforfun]

I That is, the alcohol makes the SG of the wine go below 1.00, but it shouldn't add extra ABV.

Not according to the instructions that came with my hydrometer. When it drops below 1.000, there are percentages to add to the ABV.
Maybe someone else can add to this.

 

[seth8530]

Ok, I am pretty sure that we all understand that it is the alcohol which makes the hydrometer drop down below 1.000. So imagine if we had a water that starts off at 1.000. We then add sugar to 1.100. One batch ferments down to .990 the other down to 1.000 again now which one do you think has the higher abv? Perhaps the one with with the lower density since they both started with the same amount of sugar. Thus, the drop below the 0 or 1.00 mark is still very relevant to calculating ABV.

However, one must understand that the hydrometer does not truly read potential alcohol. All it is really capable of doing is measuring the density of a fluid in units of grams/cm^3 (SG)... Other than that it does not really read the brix or the potential alcohol. It is convenient that the brix and thus the potential alcohol content of the wine can be related to SG... But it should be clear that the hydrometer does not truly measures the potential alcohol or brix.

Tak an extreme example, if you add hair gel to your wine the PA would go up, and the brix reading would also go up. However, I seriously doubt that the addition of hair gel to the must is increasing the brix or potential alcohol. However, the one reading that would be correct would be the SG because the density did truly go up by that degree.

Thus, I believe it is best to measure fermentation in terms of SG when using a hydrometer since that is the only reading the hydrometer can actually measure. I then believe it the user should use equations that relate the drop in SG to either the brix or the ABV since this IMHO is the most faithful way according to the physics at hand to perform these calculations.

 

[sour_grapes]

I thought that the ABV is whatever your potential alcohol is at the start minus the finished potential alcohol, down to 0%. I always understood that if it goes below 0, that's because of the lesser gravity (and buoyancy) of the alcohol in the finished wine as opposed to the water in the juice at the beginning. That is, the alcohol makes the SG of the wine go below 1.00, but it shouldn't add extra ABV.

As wineforfun mentioned, the amount by which the SG is below 1.000 does indeed indicate more alcohol. Water with sugar in it is denser than water without (i.e., sugar water has SG >1.000). On the other hand, a mixture of water and ethanol is less dense than water (i.e., SG < 1.000).

Now what about a mixture of all 3 (water, ethanol, and sugar)? It can have a density either above, below, or equal to 1.000. So imagine that that you have a sugar solution that started out SG>1.000, and has been fermenting for a while, and now happens to have SG=1.000. It has to be the case that there are all three substances in it, namely, water, alcohol, and some residual sugar. (If there were no residual sugar, then the density would HAVE to be <1.000.) So the wine has not yet reached its full potential alcohol. When those residuals sugars ferment, it must lower the SG below 1.000. In other words, a solution with SG <1.000 has more alcohol than a solution with SG=1.000.

(Note that, for clarity and simplicity, I am ignoring other total dissolved solids, TDS, in the solution that could raise SG above 1.000. This does not change the conclusion.)

 

[sour_grapes]

Well, Seth types faster than I do but we think alike!

 

[jamesngalveston]

http://www.davesdreaded.com/homebrew-calculator/

 

[FTC Wines]

Probably over simplified but, when my wine ferments to say .994, I just add .006 to my initial SG, then look on the hydrometer to see what the potential ABV is. Simple, no hard math, instant, who cares if I'm off a point or 2 on the ABV, if the wines GOOD!! Roy

 

[sour_grapes]

Probably over simplified but, when my wine ferments to say .994, I just add .006 to my initial SG, then look on the hydrometer to see what the potential ABV is. Simple, no hard math, instant, who cares if I'm off a point or 2 on the ABV, if the wines GOOD!! Roy

Now THAT'S a good idea.

 

[DoctorCAD]

No matter what the SG or formulas tell me, I simply state that my wine is "somewhere around 13 and a half percent". 99.999% of the population couldn't tell if it was 10% or 14%, so that 13 1/2% satisfies just about everyone.

My notes are much more clear, but I rarely ever pull them back out unless I am doing the same kind of wine.

 

[jamesngalveston]

I agree...but most couldnt tell if the wine was white are red if blindfolded.

 

[FTC Wines]

James, I agree totally, once I did a blind taste test of 2 of my Cabs & a Blackberry, 2 out of 3 thought the Blackberry was the best Cab they ever had!! Sooo 11-12-13 % it doesn't make that big of a difference, OK, maybe after 4 glasses it does!! Roy. PS I on glass 3

 

[Floandgary]

Unless exact alcohol numbers are of prime importance, I think it safe to say that most all home-made kits, buckets, and fresh picked's will fall somewhere in the 10%-12 1/2% range. These done according the generally accepted processes and not specialties. After 2 or 3 glasses, only your liver will know for sure