Question about yeast attenuation

[Beerhog]

So, a lot of brewing yeast has attenuation % listed. It is defined as the degree to which yeast ferments the sugar in a wort or must. I found this very confusing, because brewers yeast or any yeast when it is pitched into a wort or must that contains only fermentable sugars will ferment it all, provided it is within its alcohol tolerance limit. Beer wort has fermentable sugars and nonfermentable sugars. I would imagine beer yeast ferments all fermentable sugars and leaves other sugars alone. Wouldn't attenuation be a characteristic of wort and not yeast? How would the result differ, between yeast with 80% attenuation vs the one with 60% attenuation, since they both will ferment all fermentable sugars?

 

[Rob2010SS]

I'll be curious to know what the smarter people have to say to this. I'm not very educated to yeast and how they do what they do. I was always under the impression that yeast do NOT ferment out all of the sugars and that depending on how much residual extract you want left in the beer, you can base your choice of yeast on that. But WHY they do what they do, I have no clue.

 

[VikeMan]

Wouldn't attenuation be a characteristic of wort and not yeast?

It's a function of both. I'm going to over generalize here, but only a little. All the strains can use all the simple sugars. Most strains cannot use what are often called "unfermentable dextrins." But there is also a not-so-simple sugar called Maltotriose (a trisaccharide) in beer worts. Strains vary in their abilities to use Maltotriose. A few can't use it at all. Most use various portions (i.e. differing amounts, depending on strain) of it. Maltotriose is the carb that's most responsible for differences in attenuation between yeast strains with the same wort.

 

[Oginme]

The % attenuation listed in the yeast specifications is an expected test result for that strain on a standardized laboratory (all-grain barley) wort. Each recipe we brew varies from that standardized wort in a variety of ways. So you are correct in your premise that it is the performance of that strain on a given characteristic wort. Actual results will vary based upon malt types used, saccharification rests, mash time, enzymatic levels/activity of the malts used, simple sugar additions vs barley derived sugars, etc.

 

[VikeMan]

The % attenuation listed in the yeast specifications is an expected test result for that strain on a standardized laboratory (all-grain barley) wort.

White Labs lists 73-80% for WLP001 (for example). If that wide range is based on a standardized laboratory wort, their laboratory's precision is terrible.

I have heard this explanation for the published attenuation values before, but I just don't buy it. Or if it's true, there's obviously more to it.

 

[Beerhog]

It's a function of both. I'm going to over generalize here, but only a little. All the strains can use all the simple sugars. Most strains cannot use what are often called "unfermentable dextrins." But there is also a not-so-simple sugar called Maltodextrin (a trisaccharide) in beer worts. Strains vary in their abilities to use Maltodextrin. A few can't use it at all. Most use various portions (i.e. differing amounts, depending on strain) of it. Maltodextrin is the carb that's most responsible for differences in attenuation between yeast strains with the same wort.

Okay, that makes sense. What is crazy is that any article I look at that tries to explain what atenuation is does not even mention maltodextrin or non fermentable sugars.

 

[VikeMan]

Okay, that makes sense. What is crazy is that any article I look at that tries to explain what atenuation is does not even mention maltodextrin or non fermentable sugars.

Thanks for quoting my words back to me, so I saw them again. I meant to say Maltotriose (not maltodextrin).

Maltodextrin is actually a product made from non-malt starch sources. It's also mostly not fermentable, but you won't find it (the product) in most beer worts, i.e. it's not a result of a normal mash, though some of the polysaccharides typical of maltodextrin probably are. (They fall into the category of "unfermentable dextrins.")

 

[Nubiwan]

So, a lot of brewing yeast has attenuation % listed. It is defined as the degree to which yeast ferments the sugar in a wort or must. I found this very confusing, because brewers yeast or any yeast when it is pitched into a wort or must that contains only fermentable sugars will ferment it all, provided it is within its alcohol tolerance limit. Beer wort has fermentable sugars and nonfermentable sugars. I would imagine beer yeast ferments all fermentable sugars and leaves other sugars alone. Wouldn't attenuation be a characteristic of wort and not yeast? How would the result differ, between yeast with 80% attenuation vs the one with 60% attenuation, since they both will ferment all fermentable sugars?

I am interested too. I have brewed similar Amber ales and let one mash for an hour around 153 degrees. The other mashed nearly 2.5 hours and dropped from 154-146 degrees before I boiled.

My 2.5 hour beer dropped from OG 1.054 to 1.006, while my 1 mash only dropped down to 1.012. So a variance in ABV using US-05 each time.

How does my meager experiment then speak to attenuation and efficiency?

IMHO Yeast attenution is at the mercy of what temp you mash at. Efficiency can be improved (apparently) with longer mashes. At least anecdotally.