So how much alcohol is REALLY in my wine?

[BigDaveK]

Been thinking about this...

Specific gravity measures the density of the wine. Early on the SP goes down because the sugar is being consumed by the yeast. Under aerobic conditions - the bucket - yeast use the sugar for multiplying and they give off CO2. They don't start ethanol production until they're in an anaerobic environment - the carboy with airlock. So it seems to me going by the change in SG gives a VERY approximate ABV at best. Am I wrong?

I transfer to secondary between 1.020-1.030. Seems to me you want anaerobic conditions early while there's still food for the yeast to function and make a boatload of ethanol. Again, am I wrong? And is there an easy (meaning inexpensive) way to measure alcohol content?

I'm wondering if the older recipes that go under airlock from the start were on to something?

 

[sour_grapes]

I just gave a relevant reply in another thread. Check it out before contemplating too hard: Dragon Blood versus Skeeter Pee

 

[Raptor99]

As yeast use the sugar, they make ethanol. So I think you could estimate the current ABV based on the change in SG. All the SG/ABV calculators assume this.

If you have both a refractometer and a hydrometer, you could measure the current SG and current Brix, and then use this calculator to estimate ABV: Homebrew Refractometer Calculator

 

[Rice_Guy]

What is good enough?

From a label point of view
commercial wine can be off by 0.5%, without needing a new label. Commercial wine MUST have a lab number ,,, gravity difference isn’t good enough.
The basic lab bench test is accurate to about 0.1%. The capillary Vinometer is accurate to 1% but can give really bad numbers depending on the type of solids in the wine.
From a safe food point of view simply being over 5% ABV means you won’t kill yourself. From a micro point of view being anaerobic and having low pH are important.
From a blood alcohol level for driving, your body weight and time since the drink matter. A variable as size of glass will give as much error as changing ABV by two percent.

As a home wine maker I am more concerned about pH and mg of oxygen incorporated by sloppy technique.
As a QA lab person the only good way to know the number is to actually test it.

 

[balatonwine]

is there an easy (meaning inexpensive) way to measure alcohol content?

This answer I provide is very basic. Goes back to my clients who often wanted a cheap, fast solution.

I told them the old reality: You can have it quick, cheap or accurate. Pick any two.

So :

1) Cheap and Quick: use a vinometer. It will give you a quick answer of questionable accuracy. They are rather cheap. But they require the wine to be totally dry and you still should a have good one as really cheap ones will tell you distilled water has alcohol.

2) Cheap and Accurate: Use a hydrometer at start of fermentation and at the end. Do the math. Not quick but rather accurate.

3) Quick and Accurate: Send your wine sample out for analysis. The most accurate. They can often give results fast. But not necessarily cheap (but some might do small samples for very reasonable prices -- so do not hold back from inquiring).

Hope this helps

 

[Raptor99]

As a home wine maker I am more concerned about pH and mg of oxygen incorporated by sloppy technique.

I agree. If my estimate of ABV is off by 1%, who cares? As long as ABV is at least 11-12%, it is enough to protect the wine. The only reason to have even a ballpark figure is so that my guests and I can decide how much we want to drink. If they are driving home, it makes a difference if it is 11% vs. 16%. With my meads, I let them know whether it is a session mead at 5-6% ABV vs. a traditional mead at around 12-13%.

 

[winemaker81]

Dave, all calculations used for ABV are approximations. None take into account the other components in wine.

The graphed ABV curve is not a steady one. From what I've read, the formula changes according to the result, meaning one formula is used for beer (ABV in the 4% to 8% range), another for table wines (under 15%), and another for stronger wines. Note that different articles have stated different ranges, and I have no idea which is correct if any. I listed ranges for illustration, and I'm certain you can find an article that disagrees with them.

I started a post regarding this quite a while ago, but got frustrated as I couldn't determine which sources were accurate.

They don't start ethanol production until they're in an anaerobic environment - the carboy with airlock.

This is not correct. If you were close by I'd pop a bottle of 2019 Zinfandel that was fermented to near dry in Brutes. It's at ~15.7% ABV, and if you don't believe the calculation, drink a bottle then try to stand up.

I believe the correct explanation is that yeast reproduces aerobically, e.g., using O2, and it eats-n-excretes anaerobically, e.g., without O2.

 

[sour_grapes]

In the second post, I merely made a reference to a post I made in another thread. Based on how the discussion has gone so far, I now think that I should have posted the whole message again here.

I am pointing this out only because I know you will be interested, Dave. What you wrote is true of most yeast, but not entirely accurate for S. cervevisiae. Check out the Crabtree effect: Crabtree effect - Wikipedia

A few years ago, I also labored under the impression that yeast only produce alcohol in anaerobic conditions. Yeast can metabloize sugar either aerobically (i.e., respiration) or anaerobically (i.e., fermentation), but they get much more caloric benefit in aerobic metabolism. Therefore, it seemed obvious that they would use the O2 if is available. In fact, this is true for most yeast. But hat tip to @balatonwine , who taught me years ago about the Crabtree effect: It appears that beer and wine yeast choose to make alcohol, even if O2 is available. (That is probably why we like them so much! )

Here is the wiki page on it: Crabtree effect - Wikipedia
and here are a couple of fascinating papers on the mechanism and its possible origins:
An evolutionary perspective on the Crabtree effect
https://www.pnas.org/doi/10.1073/pnas.2112836118

PS: I think I am misusing the terms aerobic and anaerobic in the above explanation. It seems that those terms strictly refer to whether O2 is present or not, but does not consider whether it is used or not. Thus, the "big boys and girls" say things like aerobic fermentation when they are referring to alcohol being produced even when O2 is available. But I think my meaning in the above is clear enough, so I will leave it be.

 

[BigDaveK]

I have to say I NEVER thought I would enjoy reading about yeast metabolism! What a crazy hobby!!

To briefly recap, under aerobic conditions the yeast multiply. Under anaerobic conditions the yeast are "forced" to produce ethanol instead. The Crabtree Effect only tells me that some of the yeast will produce ethanol under aerobic conditions. Additionally, the thought as of 2019 was that the yeast don't start producing ethanol until they've reached the Hayflick Limit, the end of their replicative life cycle. Depending on the strain, yeast will reproduce (bud) 5-25 times.. And each budding happens approximately every 2 hours.

My whole point was that some of the sugar is going for reproduction and not ethanol production. I haven't as yet found a quantitative measure of how much sugar is consumed for each process. (I've read 1-2% of their body weight during fermentation but reproduction I don't know.)

So how close of an approximation are SP measurements? That's what I'm curious about. I don't need to know, just curious.

 

[winemaker81]

In the effort necessary to find the truth lies madness.

If the difference is 1 to 2 percent, I don't believe the answer is useful.

 

[cmason1957]

None of the formulas are correct. Not absolutely, anyway. They are all approximations. That is why Fermcalc gives you four or five to choose from. But, they are all within 1% of each other, so they are close enough for me.

As pointed out above by @balatonwine the only accurate measure is by a lab or use an ebulliometer.

 

[vinny]

In the effort necessary to find the truth lies madness.

Brilliant.

 

[winemaker81]

Brilliant.

So you're a H P Lovecraft fan as well?

 

[sour_grapes]

I have to say I NEVER thought I would enjoy reading about yeast metabolism! What a crazy hobby!!

To briefly recap, under aerobic conditions the yeast multiply. Under anaerobic conditions the yeast are "forced" to produce ethanol instead. The Crabtree Effect only tells me that some of the yeast will produce ethanol under aerobic conditions. Additionally, the thought as of 2019 was that the yeast don't start producing ethanol until they've reached the Hayflick Limit, the end of their replicative life cycle. Depending on the strain, yeast will reproduce (bud) 5-25 times.. And each budding happens approximately every 2 hours.

My whole point was that some of the sugar is going for reproduction and not ethanol production. I haven't as yet found a quantitative measure of how much sugar is consumed for each process. (I've read 1-2% of their body weight during fermentation but reproduction I don't know.)

So how close of an approximation are SP measurements? That's what I'm curious about. I don't need to know, just curious.

FWIW, Dave, I am in your camp here. I understood from your first post that you were interested in the fundamental question, not just whether or not it makes a significant difference. I want to know more, too.

Can you point me to any of the references you, ummm, referred to above, like the 2019 study and the Hayflick stuff? I assume (wrongly?) that this refers to the end of their budding reproduction, and then they go into sexual reproduction? Haploid vs. diploid stuff?

 

[BigDaveK]

In the effort necessary to find the truth lies madness

Okay....
"As knowledge increases wonder deepens."

If the difference is 1 to 2 percent, I don't believe the answer is useful.

Yes, "if", I agree.
But what "if" it isn't?

 

[BigDaveK]

FWIW, Dave, I am in your camp here. I understood from your first post that you were interested in the fundamental question, not just whether or not it makes a significant difference. I want to know more, too.

Can you point me to any of the references you, ummm, referred to above, like the 2019 study and the Hayflick stuff? I assume (wrongly?) that this refers to the end of their budding reproduction, and then they go into sexual reproduction? Haploid vs. diploid stuff?

I've only glanced at the sexual reproduction aspect. I think I enjoy reading about yeast because they are so incredibly complex and there are still so many unknowns. It's a little crazy but I find them "beautiful".

One reference is The Alcohol Textbook. It's the 4th edition, haven't seen the updated 6th edition yet.

https://edisciplinas.usp.br/pluginf...urce/content/1/The_Alcohol_Textbook- 4 Ed.pdf
The other reference was saved as a PDF and I don't have a link. It's really interesting.

Yeast Life Span and its impact on Food Fermentations - Aranda, Orozco, Picazo, Matallana

One thing that really strikes me is that the amount of research being conducted on the lowly yeast is mind boggling.

 

[David Violante]

It is only madness until it all of a sudden it becomes wonder. It’s just getting through the effort of the madness… these are all wonderful reads!

 

[winemaker81]

Yes, "if", I agree.
But what "if" it isn't?

Good question. I did a fair amount of research and identified no conclusions I trusted.

You may do better than I did, and if so, great!

One thing that really strikes me is that the amount of research being conducted on the lowly yeast is mind boggling.

Look at it from a different POV -- yeast is big money.

https://wineamerica.org/policy/by-the-numbers/
US grape production (not wine production) is valued at $6.5 billion USD. In 2018 wine exports were valued at $1.46 billion USD. The amount of research is not surprising in light of those numbers.

Note that the USA accounts for 12% of the world's production -- wine is big business across Europe, South America, Australia, South Africa, and many other places.

Well funded yeast research is not a surprise in this light.

The drawback for most of us, is that research is funded by and geared towards professional wineries. Lab tests whose cost makes you or me choke up a hairball are simply the cost of doing business.

It doesn't help that most of the researchers appear to get brownies point for every time a reader has to refer to a thesaurus or chemistry/biology dictionary. I keep them open in other tabs when reading. This is one reason I like the Australian Wine Research Institute a lot -- I can read most of the papers without having to look things up in every sentence. [Which doesn't mean it's not technical and that I haven't spent a fair amount of time researching terms.]

Plow on and keep researching!

 

[sour_grapes]

Yes, "if", I agree.
But what "if" it isn't?

Okay, but now you know that your initial premise was false. Our yeasties do make alcohol, even in an aerobic environment.

Now consider that commercial wineries test their ABV. The values they report are broadly consistent with the SG drop methods. We don't know, of course, their starting SG and ending SG for each wine. However, we know broadly what the Brix is for hot Cali grapes and hot Spanish grapes and cool Burgundy grapes and cool Mosel Valley grapes. And we broadly know the ABV for hot Cali regions and hot Spanish regions and Burgundy and Mosel Valley. And these results do not differ by any large extent from what the SG drop would tell you.

But if you really gots to know... Hmmm, do I see an ebulliometer in Dave's future?

 

[vinny]

So you're a H P Lovecraft fan as well?

No!

Never heard it before, but I know a number of truth seekers that are bordering on madness!

I laughed when I saw it, because when I read the OP I was thinking how many rabbit holes does @BigDaveK have in his backyard? He was in one last week and now he has his foot caught in another!