[RPIScotty]

How do you go about increasing the attenuation of a particular yeast?

The reason I ask this is because in reading and re-reading BLAM, I see many of the Trappist examples, notably the Chimay and Westmalle beers, with lower OG than one would expect but with ABV spot on. They are getting there with high levels of attenuation.

I of course understand that the strains available to is are not the yeast used in the Trappist breweries, but am wondering what it might take to reach those levels of AA with commercially available yeast.


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[klickitat jim]

Me? Low long mash, subbing at least 10% of the OG from grain with sugar, oxygenation, slow steady ramping fermentation temp as krausen falls, not allowing temp to drop until its done done.

[Stevie]

Simple sugars

[HoosierBrew]

Mash low and long, sub in simple sugars, limit crystal type malts, use highly attenuative strains.

[RPIScotty]

All great info but a bit like basic Belgian brewing 101. Those are all things aimed at achieving the maximum attenuation from a given yeast's manufacturers specs.

I'm talking getting 85+ %AA. I've gotten in the high 70s, low 80s with WY 3787 using all the above referenced methods.

What more advance techniques can get me higher? Obviously repitching from a strong fermentation is a must but are there ways to selectively increase the ability for a yeast to attenuate?


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[Stevie]

It all comes down to the fermentability of the wort. That is where low mash temp and simple sugars come in.

[dmtaylor]

If you really want to jack 'er up, then pitch a pack of Belle Saison yeast after the first 2 days of primary fermentation with your other yeast.  The Belle Saison will eat up everything that the first yeast won't.  I've never done this but it should work.  Final gravity will be about 1.002 -- no exaggeration.

[troybinso]

Just use WY3711 French Saison yeast.

You can give it just about any wort you can make and ferment somewhere between 64F and 84F and you will get 90%+ attenuation. I recently brewed a beer with this yeast that had a 1.042 starting gravity and 5.5% abv.

[klickitat jim]

I've heard them Belgians use Brett too. That's another way. Works good for me, especially with saisons

[RPIScotty]

Thanks fellas. Again, great round of information.

I was thinking more (I probably could have made it clearer) from the standpoint of modifying the yeast through repitching, etc.

Obviously Chimay, Westmalle, Rochefort and the like have selectively "bred" (for lack of a better word) their yeast over the years to obtain the way above average levels of attenuation they get. I know, for instance, that the CSI recipe for Grand Reserve quotes 1.077 OG/1.009 FG, which by my calcs is ~88% AA!

Unless of course I'm just confused. I realize I could be just neglecting the fact that people are really waiting it out for those few points of attenuation, but there has to be a limit on the commercially available yeast. Are you guys getting >85% with your Belgian brews?

...not allowing temp to drop until its done done.

This may ultimately be it on the homebrew level unless through selection and repitching you can "cultivate" high attenuation. I may be showing my ignorance here.


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[narvin]

I wouldn't focus on strain mutations.  They were using their yeasts for years by the time the yeast banks got them.

The first generation of yeast grown up from laboratory media just isn't going to perform as well.  Many of the Trapppists repitch from smaller beers into bigger beers.  Westmalle top crops very active yeast.  I've experienced this most with the Rochefort strain, where anything above 1.070 for a first generation yeast is going to be an under attenuated disappointment by Trappist standards.

With 15-20% sugar, there's nothing that makes 88% attenuation unattainable.  The yeast company guidelines are for an all-malt wort.  If you're having trouble with first generation yeast, you can use incremental sugar feedings.

[RPIScotty]

With 15-20% sugar, there's nothing that makes 88% attenuation unattainable.  The yeast company guidelines are for an all-malt wort. 

Thank you for clarifying this.

All great info but a bit like basic Belgian brewing 101.

I didn't mean to insult anyone with this comment by the way. I know you all have tough skin around here ( ) but figured i'd say it anyway.

[hopfenundmalz]

Pull up the Greg Doss presentation from 2012. Nice graph of attenuation vs strain on page 18. The Belgian Trappist strains are low 1214 Chimay, to high 1762 Rochefort. None are 88%.

[RPIScotty]

Pull up the Greg Doss presentation from 2012. Nice graph of attenuation vs strain on page 18. The Belgian Trappist strains are low 1214 Chimay, to high 1762 Rochefort. None are 88%.

Yet people are getting 88%. That's really the question. How to get those high values.

[S. cerevisiae]

Obviously Chimay, Westmalle, Rochefort and the like have selectively "bred" (for lack of a better word) their yeast over the years to obtain the way above average levels of attenuation they get.

The word is you are searching for is "selected."  These strains have been selected over the years via selective pressure.  In a nutshell, one can think of selective pressure as the result of serial repitching in a specific environment. It is basically Darwinism applied to yeast.  The fittest cells for the environment live, and those that cannot hack it die off. 

All yeast strains drift genetically over time, which is why most breweries that have one or more house strains keep seed cultures.  A seed culture can be thought of as a cell that was selected for its performance at a specific point in time.  That cell's off-spring become the house strain.  Seed cultures are usually keep in cryostorage at at least -80C.  If a brewing company has deep pockets or uses an organization such as the NCYC in the UK or the ATCC in the United States as a culture repository, it will choose to store its seed cultures under liquid nitrogen at 77 Kelvin (-196C/-321F).  Cultures can be maintained indefinitely at 77 Kelvin.