How does a low attentuating yeast work?

[TechFanMD]

Danstar Windsor is often shown to have low attenuation, leaving a fairly high final gravity. This is clearly not due to the lack of fermenables, as a pitch of a different yeast can bring it down many more gravity points.

For example, it is common for this yeast to stop at around 1.025 on a specific beer brewed by hundreds of brewers, but if you pitched S05 either instead of Windsor or even pitch it when Windsor stops, it will take it down to 1.012-1.015 or so.

For 'moderate' or 'low' attenuating yeasts, what is the mechanism that causes them to stop? If it were simply the alcohol level, wouldn't they have difficulty carbonating via a prime and bottle process?

Are there other factors that cause these low attenuating yeasts to stop at high FG even though there are still viable yeast?

 

[Silver_Is_Money]

One reason why Windsor finishes with a high SG is that it is nigh on totally incapable of fermenting a type of sugar called maltotriose, whereas many other yeasts can moderately to readily ferment this type of sugar. Maltotriose is a standard component among the the various types of present wort sugars. I believe more of it may be formed if you mash at higher temperatures.

 

[TechFanMD]

One reason why Windsor finishes with a high SG is that it is nigh on totally incapable of fermenting a type of sugar called maltotriose, whereas many other yeasts can moderately to readily ferment this type of sugar. Maltotriose is a standard component among the the various types of present wort sugars. I believe more of it may be formed if you mash at higher temperatures.

That is very helpful. Until I saw your post and was able to look up Maltotriose as a factor, I wasn't having any luck......search results generally came up with 'stuck fermentation' articles...which as you understand isn't my question.

I wish there was a chart of yeast strains vs attenuation. I like Windsor well enough, and don't want this particular beer to dry out too much, but more than it is.

 

[RM-MN]

Changing conditions of the ferment can change the attenuation. Pitch rate is one of these conditions. Pitch lots of yeast and you get a lower (moderately lower) FG. Changing the temperature is another. Start the ferment cool, then raise it after a few (3-5) days and the yeast likely will work a little harder.

 

[Vale71]

This is still the subject of (as yet rather inconclusive) academic research. While it's a fact that low attenuating yeast strains do leave maltotriose mostly untouched, some extreme strains even ferment maltose only partially leading to extremely low attenuations. Researchers haven't been able to prove that low attenuators are either genetically or morphologically incapable of fermenting maltotriose, leaving the possibility open that low attenuation is simply due to high flocculation. Flocculation is unfortunately the subject of as much research as attenuation, so the jury is still out on both issues.

 

[Northern_Brewer]

Most yeast producers will have attenuation details listed somewhere on their website (like the bottom of here) but you can't directly correlate them as the degree of attenuation depends on what you're fermenting. So the fermentables in wine and mead are almost all in the form of simple sugars, so even a "low" attenuating yeast like Windsor will give apparent attenuations of near 100% in wine, but generally attenuations are quoted for a standard beer wort (different for each manufacturer) that is something like 65-70% simple sugars, 10-15% maltotriose (chains of 3 glucoses), and 20% complex carbohydrates. So a typical low attenuating yeast like Windsor that can't metabolise maltotriose will come out at 65%, a high-attenuating yeast like S-05 that can do maltotriose will be closer to 80%, a lot of British yeasts have some activity against maltotriose and so come out at 70-75%, diastaticus yeasts including many Brettanomyces have extra enzymes that can chew complex carbohydrates and so can attenuate close to 100%.

But it does depend on the exact composition of the wort, and also on some other factors aside from enzymes - fast-dropping yeasts can drop out before they've finished working, and can be pushed to attenuate more by rousing.

Yeasts tend to be good at one thing or another - traditionally breweries used a multi-strain yeast, which included strains that dropped quickly, ones that attenuate well and ones that gave good flavour, so you got the benefit of all of the best qualities.

Allegedly both Windsor and Nottingham were originally isolated from the same brewery, so that's an obvious combination of a good-flavour-but-poor-attenuation-and-poor-dropping yeast with one that is cleaner but drops well and attenuates pretty well too.

 

[Silver_Is_Money]

Allegedly both Windsor and Nottingham were originally isolated from the same brewery, so that's an obvious combination of a good-flavour-but-poor-attenuation-and-poor-dropping yeast with one that is cleaner but drops well and attenuates pretty well too.

Any guess as to which brewery that might be?

 

[Northern_Brewer]

Any guess as to which brewery that might be?

Sadly not. If I had to guess, then my guess would be one of the old East Midlands breweries like Home, but it would be nothing more than a guess.

 

[STMF]

I wish there was a chart of yeast strains vs attenuation. I like Windsor well enough, and don't want this particular beer to dry out too much, but more than it is.

Not complete but alot of strains: http://www.shegoguebrew.com/p/yeast-strains.html