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barracudamagoo · 07-08-2009, 04:06 PM

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?

WorryWort · 07-08-2009, 04:17 PM

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

**JLem** · 07-08-2009, 04:19 PM

unfermentable sugars

barracudamagoo · 07-08-2009, 04:23 PM

Quote:

Originally Posted by noeldundas

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

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).

WorryWort · 07-08-2009, 04:32 PM

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?

**JLem** · 07-08-2009, 04:41 PM

Quote:

Originally Posted by noeldundas

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'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.

WorryWort · 07-08-2009, 06:53 PM

Quote:

Originally Posted by JLem

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.

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.

barracudamagoo · 07-08-2009, 07:12 PM

Quote:

Originally Posted by JLem

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.

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.

**JLem** · 07-08-2009, 07:15 PM

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.

WorryWort · 07-08-2009, 09:03 PM

Quote:

Originally Posted by JLem

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.

That's what I was looking for.