Confusion - Attenuation in Beer vs Champage Yeast

[dogbert]

Background: Mead and wine maker for several years, started getting into all grain beer brewing a year ago.

So, to my knowledge, the higher the attenuation of a yeast, the more of the sugars are converted to alcohol. When I make meads using champagne yeast, they dry out to as low as 0.994 FG. At this point, effectively all of the sugars have been converted to alcohol, CO2, etc.

So, why does attenuation take place at all? Is it because there are sugars in the beer that can't be fermented by the beer yeast (in my case, ale yeast)? Most wikis on the topic basically say that attenuation is a measure of how much sugar is not fermented. (http://brewwiki.com/index.php/Attenuation). This doesn't make sense, because if I let a fermentation finish, then add more fuel (eg: sugar), then fermentation starts again.

So, is attenuation really just a measure of the average case OG/FG ratio, or something similar? Or is a measure of the minimum residual sugar content in solution before the yeast stops its conversion process? I'm puzzled as to why an ale yeast can't dry out a batch of wort to 0.995 FG like a wine or champagne yeast, and instead seems to taper off around 1.007 FG.

Thank you all in advance for your advice.

 

[RM-MN]

When you make beer from all grain, your temperature that you mash determines to a great extent the amount of fermentable sugars. If mashed in the higher range, there will be more unfermentable sugars produced. These add maltiness and body to the beer. To further confuse the issue, some of the other grains add unfermentable sugars too, such as your crystal malts or dark malts. Ale yeast can only ferment part of the sugars in the beer so you have limits to the attenuation.

 

[pdxal]

Apparent attenuation is the percentage of OG that is fermented to alcohol and CO2 by the yeast. OG-FG/OG=apparent attenuation.
In beer there are unfermentable sugars and starches that make up the gravity, and contribute to flavor and balance with bitterness from hopping. In wine and mead there are (primarily) fermentable sugars.
Most beer yeasts top out around 75% attenuation since they are dealing with a mixture of sugars and dextrins in wort.

 

[JLem]

There are two things to consider here:
1) what type of sugars are in the wort or must (?? Not sure what it's called in wine/cider/mead)?
2) what types of sugars can the yeast metabolize?

All yeast can fully metabolize simple sugars, so all yeast (champagne or wine or ale or lager) will be able to ferment wines and ciders down to 1.000 or less.

Wort is much more complex in terms of sugars, so there will be some left behind - how much depends on the yeast strain. Lager strains can metabolize more types of sugars than ale strains, so lagers tend to attenuate lower than ales. Wine strains are essentially just different ale strains, so they would give you similar attenuation as ale strains. Champagne yeast is different, but will still leave some sugars behind in beer - I think it is similar to some ale strains in this regard.

 

[dogbert]

Thank you all very much. This clears up my earlier confusion.

Cheers!

 

[william_shakes_beer]

Champagne yeast ferments out more sugars than beer yeast. I know some beer brewers that hasve report using to champagne yeast for big beers that they want to dry out and/or boost the alcohol.

Also, Honey is mostly fementable sugar. Even beer yeast wil eat it, which is why honey malt IMHO is a better choice for honey flavor in beer than honey.

 

[JLem]

Champagne yeast ferments out more sugars than beer yeast. I know some beer brewers that hasve report using to champagne yeast for big beers that they want to dry out and/or boost the alcohol.

I'm not certain that this is true (I'm also not certain it is not true)...my understanding however is that champagne yeast cannot ferment complex sugars like maltotriose...neither can most/all ale yeasts, though many/all lager yeasts can. Champagne yeast becomes useful for its ability to handle adverse brewing conditions (low pH, low oxygen, high ABV)...so, when other yeasts succumb to these conditions, champagne yeast can keep chugging along...assuming there are still sugars in there that it can metabolize. So, champagne yeast is used in big beers, not because it can metabolize more of the sugars, but because it can survive longer under the conditions.

 

[william_shakes_beer]

I'm not certain that this is true (I'm also not certain it is not true)...my understanding however is that champagne yeast cannot ferment complex sugars like maltotriose...neither can most/all ale yeasts, though many/all lager yeasts can. Champagne yeast becomes useful for its ability to handle adverse brewing conditions (low pH, low oxygen, high ABV)...so, when other yeasts succumb to these conditions, champagne yeast can keep chugging along...assuming there are still sugars in there that it can metabolize. So, champagne yeast is used in big beers, not because it can metabolize more of the sugars, but because it can survive longer under the conditions.

When my long held beliefs are challenged in replies such as this, I take the opportunity to refer to authorative sources. SOOOOO

I browsed to White labs yeast liibrary. In general their ale yeasts list alcohol tolerance as low, medium and high. No numbers. However, their champagne yeast (WLP715) lists alcohol tlolerance as 15-16%. Optimum Temp range, however is narrow, 62-68%, similar to an ale yeast. No mention of other factors.

Sooo, looks like I was wrong. Thanks.