Differences in attenuation between strains

[Shift]

Why do different strains have different attenuation?

Shouldn't they all be able to eat the same sugars?

 

[remilard]

Why do different strains have different attenuation?

Shouldn't they all be able to eat the same sugars?

Some strains flocculate more. Once the fermentation slows, flocs will leave suspension faster than powdery yeast. You'll find that there is a pretty good correlation between attenuation and flocculation.

On the other hand, the numbers reported by white labs and wyeast are misleading. When they say that English yeast as 68% attenuation that is in some nominal English wort with crystal malt and a high single infusion mash temp. When they say some belgian yeast as 82% attenuation, that is in some nominal belgian wort with a bunch of sugar.

If you put the same two yeast in identical wort, they would never actually attenuate 14% different.

 

[thisone]

https://www.homebrewtalk.com/wiki/i...ation#Yeast_Strain_Differences_in_Attenuation

Though yeast strains are able to ferment all the sugars in the beer, they usually don't get to. In contrast to a forced ferment test, beer is generally fermented at lower temperatures, with smaller pitching rates and without constant rousing. Because of that the yeast will not get a chance to ferment all fermentable sugars in the wort. Flocculation will cause it to drop to the bottom or collect on the surface where it doesn't have as much contact with the sugars anymore. Because of nutrient depletion and or high alcohol levels cells die before they get a chance to ferment every last bit of sugar in the wort. The result is left over fermentable sugars that play an important role in the character of the finished beer. The closer a beer's attenuation is to its limit the drier and less sweet it will taste. When looking at the attenuation ranges given for commercial yeast you will notice that the less flocculating a yeast is, the more attenuative it will be. This makes sense as the poorly flocculating yeasts will remain in contact with the wort for a longer time. The beech wood aging process used by Anheuser-Bush to brew Budweiser does exactly that without relying on poor flocculation alone; it maximizes the contact area between beer and yeast.

 

[Calder]

I disagree with the previous post.

Yes, more flocculating yeast may result in less attenuation because it's dropped out, but Hef yeast don't ferment to dry, and they stay is suspension for a long time. Also, when you bottle and add priming sugar, it usually primes, meaning there is yeast still working.

The real answer is that different yeast have different abilities in converting the different complex sugars in worts.

 

[camus]

Some strains flocculate more. Once the fermentation slows, flocs will leave suspension faster than powdery yeast. You'll find that there is a pretty good correlation between attenuation and flocculation.

On the other hand, the numbers reported by white labs and wyeast are misleading. When they say that English yeast as 68% attenuation that is in some nominal English wort with crystal malt and a high single infusion mash temp. When they say some belgian yeast as 82% attenuation, that is in some nominal belgian wort with a bunch of sugar.

If you put the same two yeast in identical wort, they would never actually attenuate 14% different.

I do not think this is entirely correct, high mash temps and crystal malts have higher FG's because some of the resulting wort is not fermentable. White labs uses same wort to compare strains.


"Please note that these tests do not necessarily reflect the values you would get on your own beers (for more on testing your beers, read below), given different recipes and brewing conditions"



"Attenuation

Apparent attenuation percentage is the percentage of sugars that yeast consume. Attenuation varies between different strains. The fermentation conditions and gravity of a particular beer will cause the attenuation to vary, hence each strain of brewers yeast has a characteristic attenuation range. The range for brewers yeast is typically between 65-85%. "

Further reading:

http://www.whitelabs.com/beer/trial_fermentations.html