Beer vs Wine Fermentation

A question I had not thought about until the wife asked me. Why does beer, unlike wine, not ferment all the way out? Seems like it stops around 70% or so. Is the yeast used not alcohol tolerant above X%? Unfermentable sugars?

Ex: If I start a beer and a wine at 1.050 SG, the beer will go to something like 1.013; however, the wine could go all the way to 0.990.
What's up with that?

Maltose Vs. Fructose. And there are different yeasts used.

unfermentable sugars

noeldundas said:

Maltose Vs. Fructose. And there are different yeasts used.

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So I'm presuming there is a higher concentration of maltose in the beer, resulting in a higher concentration of unfermentable sugars. Thus why it will only ferment to x.xxx S.G. (say 25% maltose or so).

Sorry I was sort of brief.

There is no fructose in beer, unless you add fruit. And there is no maltose in wine. (I think? someone might correct me)

I don't know the science exactly, or the reasons why, but fructose ferments better than maltose. I believe that yeast just has an easy time eating fructose and sucrose as regular sugar will also ferment completely, which is why people add it to get the FGs lower. Also, the average wort still has a percentage of unfermentables (various dextrines, and possibly some starches), of course, where grape juice is mostly water and fructose.

I have to imagine the yeast differences will have an effect as well.

Sounds like we need to find someone who has done an experiment on Ed's Apfelwien fermented with wine yeast, vs. one with ale yeast. I wonder how the FG's varied?

noeldundas said:

I don't know the science exactly, or the reasons why, but fructose ferments better than maltose. I believe that yeast just has an easy time eating fructose and sucrose as regular sugar will also ferment completely, which is why people add it to get the FGs lower. Also, the average wort still has a percentage of unfermentables (various dextrines, and possibly some starches), of course, where grape juice is mostly water and fructose.

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I'm pretty sure both maltose and fructose ferment completely. The difference between beer and wine (and ciders) is that beer (wort) also contains a number of unfermentable dextrins. The amount of unfermentable dextrins is dependent on a number of things including the type of malt used and the temperature and duration of the mash.

Like you said, wine and ciders are mostly fructose and water, so they tend to ferment out.

JLem said:

I'm pretty sure both maltose and fructose ferment completely. The difference between beer and wine (and ciders) is that beer (wort) also contains a number of unfermentable dextrins. The amount of unfermentable dextrins is dependent on a number of things including the type of malt used and the temperature and duration of the mash.

Like you said, wine and ciders are mostly fructose and water, so they tend to ferment out.

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yeh i'm not sure about my claim there, i recall having heard that, but don't know the source.

I'm researching this now, because I'm interested. My hypostesis is that maltose and fructose will produce differing amounts of ethanol when fermented because they are different compounds. Further I'd assume fructose to be higher since it's sweeter - but who knows.

If that is true that would also lower the gravity of wine, because ethanol is below 1.000. I.e. If you ferment two sugars equally (same attenuation) but one produces more alcohol per gram than the other that one will have a lower FG.

I've also learned that wort is about 8-15% sugar (depends of course), and of that only about 75% is fermentable. This rate should also be higher in wine, but I can't find proof yet.

JLem said:

I'm pretty sure both maltose and fructose ferment completely. The difference between beer and wine (and ciders) is that beer (wort) also contains a number of unfermentable dextrins. The amount of unfermentable dextrins is dependent on a number of things including the type of malt used and the temperature and duration of the mash.

Like you said, wine and ciders are mostly fructose and water, so they tend to ferment out.

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I did a little looking, and maltose and fructose are fermentable; but dextrin/maltodextrin are not.
Essentially, it is that wort contains a higher percentage of unfermentables than does wine. I think the question is answered; however, feel free to elaborate on the details.

Well, maltose is a disaccharide, composed of two glucose subunits, and fructose is a monosaccharide. The yeast first need to break down the maltose into individual glucose molecules before fermenting them. Individual molecules of both glucose and fructose should yield the same amount of ethanol and CO2 since both are 6-carbon compounds. Since the molecular weight of maltose (342) is about twice that of fructose (180), and since the maltose contains twice as many potential monosachharides, an equal amount of each sugar will yield a roughly equal amount of monosachharides and thus an equal amount of ethanol.

Yeast apparently utilize glucose preferentially over fructose - I'm assuming because fermentation of the fructose requires additional steps. However both glucose (via maltose) and fructose will eventually be fermented.

To the original question - wine must contains fewer unfermentable compounds (though it does contain some) than does wort.

JLem said:

Well, maltose is a disaccharide, composed of two glucose subunits, and fructose is a monosaccharide. The yeast first need to break down the maltose into individual glucose molecules before fermenting them. Individual molecules of both glucose and fructose should yield the same amount of ethanol and CO2 since both are 6-carbon compounds. Since the molecular weight of maltose (342) is about twice that of fructose (180), and since the maltose contains twice as many potential monosachharides, an equal amount of each sugar will yield a roughly equal amount of monosachharides and thus an equal amount of ethanol.

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That's what I was looking for.

o I'm presuming there is a higher concentration of maltose in the beer, resulting in a higher concentration of unfermentable sugars.

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The unfermentable sugars in malt are much more complex than maltose. They are typically branched and have bonds that cannot be broken during the mashing process. The yeast can't absorb them, much less ferment them.

Palmer has an amusing analogy involving trees, branches and rakes in How to Brew.

I think you have to also remember that alcohol (ethanol) has a specific gravity of 0.815 (I think). Therefore, wine which is higher in alcohol will show a relatively lower SG simply because it has a higher concentration of ethanol per volume. This dosen't explain the complete difference in SG readings between beer and wine but it does explain some of the difference.

I'm still a noobie, but I have read that different yeasts are better at eating different complex sugars. Also, ale & beer yeasts have a lower alcohol tolerance, so they start to die off before they can finish consuming all the available sugar. Wine yeasts can tolerate more alcohol so they keep working till they consume most of the fermentables. If you read through some of the apfelwein posts there are folks who have made it with ale yeasts and with montrachet wine yeast, which is a higher alcohol yeast. You can get about twice the ABV with montrachet or some of the other wine yeasts. Another interesting experiment would be to try a wine yeast in a batch of wort and see what the results are. Dave Miller's homebrewing books explain a lot of the science of fermentation--some really good reading there.

I think differences in FG is more then just what kind of fermentable sugars are around for yeast metabolism. Gravity readings just don't take sugar into account: it's the overall density of all compounds in solution. Wine has a much simpler set of compounds then beer: it's mainly sugars from grapes.. where beer wort has unfermentable sugars, proteins, and lipids from specialty grains that still stay in solution after fermentation is done (and add to different flavors). This is, of course, considering "average" gravities for a typical wine or beer. Particular wine yeast strains, since they were developed for higher alcohol, can do a better job at surviving higher alcohol environments.

Fructose is Dextrose that has one more link in the molecule chain broken. They are the same compound with the melectular structure changed. the are both corn syrup

sub-zero said:

Fructose is Dextrose that has one more link in the molecule chain broken. They are the same compound with the melectular structure changed. the are both corn syrup

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Yes - fructose and dextrose/glucose are isomers - they have the same chemical formula (C6H12O6), but the atoms are arranged differently (see structures here). However, they're not both "corn syrup". "Corn syrup" is 100% glucose. "High fructose corn syrup" is a mix of glucose and fructose - some of the glucose molecules have been converted to fructose, creating a sweeter sweetener.

I'm still a noobie, but I have read that different yeasts are better at eating different complex sugars. Also, ale & beer yeasts have a lower alcohol tolerance, so they start to die off before they can finish consuming all the available sugar. Wine yeasts can tolerate more alcohol so they keep working till they consume most of the fermentables.

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While it is true that some yeasts have higher alcohol tolerance than others, this is not usually why wine FG is lower than beer FG. In beers, the alcohol content does not usually reach a high enough level to have a real impact on the yeast - this is why we can bottle condition. The beer FG stops at 1.015 (or whatever) not because the yeast have stopped working, but because there are still any number of unfermentable compounds in there (as davesrose said above, not just dextrins, but also proteins and lipids). If you used a wine yeast in your wort, I do not think the FG would be any lower.

I think you have to also remember that alcohol (ethanol) has a specific gravity of 0.815 (I think). Therefore, wine which is higher in alcohol will show a relatively lower SG simply because it has a higher concentration of ethanol per volume.

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This raises an interesting issue. Let's say you have two beers that finish with a FG of 1.015. However, one of them started with a higher SG, thus has a higher ethanol content. This would mean that the higher alcohol beer would actually be sweeter at 1.015 than the lower alcohol content beer, right?

Sorry.... read post below

JLem said:

This raises an interesting issue. Let's say you have two beers that finish with a FG of 1.015. However, one of them started with a higher SG, thus has a higher ethanol content. This would mean that the higher alcohol beer would actually be sweeter at 1.015 than the lower alcohol content beer, right?

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I think that it would be sweeter. But I don't think it would make a huge difference because the effect of the extra alcohol would be small since beer is relatively low in alcohol. But it does make sense to me. I guess that's why you should trust your taste more than your calculations.

However, they're not both "corn syrup". "Corn syrup" is 100% glucose. "High fructose corn syrup" is a mix of glucose and fructose - some of the glucose molecules have been converted to fructose, creating a sweeter sweetener.



I make Dextrose and then convert it to fructose for a living and I can assure you they are made 100% out of corn stach. They are both corn sweeteners may have been a better way for me to put it. But I understand what you are saying.