Understanding Yeast Attenuation

[flowerstomper]

Hi All -

I have a question regarding the yeast attenuation that manufacturers sometimes quote on their product information sheets.
For a working example, White Labs California Ale Yeast, where 73-80 (% I assume) is cited.

If I consider this explanation from this website - it uses the analogy of 'how much food is left on the table'.
I find this difficult to understand in relation to brews going 'dry'.

Using an example with numbers -

From this table - If we assume: we added 308g of sugar to 1L of water - it has a SG of 1.115, or a available alcohol of 15%-ish depending on methodology.
Using the above understanding of yeast attenuation - 115 x (1-0.8) = 23 - so we can expect, the yeast if it leaves '20% on the table' - it can only ferment to final gravity of 1.023 - which leaves me with a sweet end product, and an alcohol content of around 12%, despite the available alcohol and the yeast tolerance permitting 15% (assuming ideal conditions).

Is this right, or am I missing something?

Additionally: starting with a lower gravity wort - this definition of Attenuation would similarly suggest I would never be able to hit 1.000 - unless I had a 100% attenuating yeast - which I am not sure is consistent with practical experience. In fact this the website that provides this explanation of attenuation gives the following exact example:

In the example above, if you were to prepare a wort with an original gravity of 1.050 and ferment it with a strain whose published apparent attenuation is 80 percent, then you could reasonably assume that your beer’s final gravity would end up around 1.010.

Thanks for the feedback & responses in advance - always looking to understand what I'm doing better.

 

[day_trippr]

Without delving into the actual numbers, and assuming a respectable pitch-to-OG*volume, what the yeast leave behind that are classified as "sugars", are mostly if not all dextrins - long chain carbs - that for the most part are not perceived as "sweet", but do have an effect on "mouthfeel"...

And welcome to HBT, @flowerstomper


Cheers!

 

[VikeMan]

Without delving into the actual numbers, and assuming a respectable pitch-to-OG*volume, what the yeast leave behind that are classified as "sugars", are mostly if not all dextrins - long chain carbs - that for the most part are not perceived as "sweet", but do have an effect on "mouthfeel"...

I'll just add that some of what most yeast strains leave behind is some portion of the maltotriose (a sugar). In fact, it's the portion of maltotriose used/not used that accounts for the differences in attenuation between most strains.

 

[flowerstomper]

@day_trippr Thanks!

Is it right to summarise as follows then: the listed attenuation is a general guide and has some assumption as to unfermentable sugars in the wort. If there is only fermentables, say sugar (100% sucrose) + water, the attentuation listed is not meaningful.

Cheers all

 

[VikeMan]

Is it right to summarise as follows then: the listed attenuation is a general guide and has some assumption as to unfermentable sugars in the wort. If there is only fermentables, say sugar (100% sucrose) + water, the attentuation listed is not meaningful.

Yes. I would go a step further and say that the listed attenuation ranges are not even necessarily valid with certain worts, i.e. the wort's attenuability can cause the attenuation with that strain to be higher or lower than the published range.

 

[pricelessbrewing]

The listed attenuation is for a standardized grain bill, usually 100% base malt that undergoes a congress mash (or a version of it), or simply a mass produced extract, and is the apparent attenuation.

If you're not using a grain bill or a mash temp that's similar, the attenuation is going to differ. If you're adding sugars, the attenuation is going to be higher than listed as simple sugars like glucose/sucrose are 100% attenuative (100% real, ~121% apparent).

 

[VikeMan]

The listed attenuation is for a standardized grain bill, usually 100% base malt that undergoes a congress mash (or a version of it), or simply a mass produced extract, and is the apparent attenuation.

I have heard a similar thing before. But if true, how in the world do they come up with a (quite wide) range of 73-80%?

 

[Vale71]

I have heard a similar thing before. But if true, how in the world do they come up with a (quite wide) range of 73-80%?

They just take a wild guess based on some test batches they've run. Attenuation is one of the things there is no standardized test for.

 

[VikeMan]

They just take a wild guess based on some test batches they've run. Attenuation is one of the things there is no standardized test for.

My theory has always been that they assign ranges based on what they believe are typical attenuations for the (range of) styles typically brewed with the strain. If so, it could explain the rather wide 73-80% assigned to WLP001 and (for example) the narrower 74-78% assigned to WLP400.

Unfortunately, they are often taken as some sort of real physical bounds. "My milk stout fermentation is stuck at x.xxx."

 

[pricelessbrewing]

My theory has always been that they assign ranges based on what they believe are typical attenuations for the (range of) styles typically brewed with the strain. If so, it could explain the rather wide 73-80% assigned to WLP001 and (for example) the narrower 74-78% assigned to WLP400.

Unfortunately, they are often taken as some sort of real physical bounds. "My milk stout fermentation is stuck at x.xxx."

Probably true. I should ask my friends at a couple yeast labs. Really wish there was better info.