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Brews & Views Bulletin Board Service * Brews and Views Archive 2004 * Archive through August 30, 2004 * Yeast Attenuation < Previous Next >

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Question for Fredrik regarding maltotrioseFredrik24 08-30-04  05:14 am
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Chad Dickinson
Intermediate Member
Username: Icehouse

Post Number: 317
Registered: 02-2003
Posted on Friday, August 20, 2004 - 11:57 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

In this months BYO, there are several interesting Hoppy beer clones. One thing seemed to and continues to stand out to me though.

I notice many times their OG and FG seem to imply an attenuation rate that is unattainable by the yeast given.

For example, one of the recipes, (can't remember which one) stated an OG of 1.075 and an FG of 1.010. WLP001 or WY1056 is the yeast to be used. This would imply an attenuation rate of almost 87%, and WLP001 is attenuative up to 80% and WY1056 is attenuative up to 77%. What gives?
 

Dan Listermann
Intermediate Member
Username: Listermann

Post Number: 368
Registered: 03-2004
Posted on Saturday, August 21, 2004 - 12:41 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

The published attenuation rates of yeast cause a lot of confusion. They are really comparative rates to other yeasts and cannot be depended upon for a given wort. Far and away the primary determiner of attenuation of a wort is what it, the wort, is composed of. The yeast can vary the attenuation only a few points. I would far rather rate yeasts as "low, medium or high" attenuaters. Software that attempts to predict FG based on published attenuation rates are misleading.
 

Chad Dickinson
Intermediate Member
Username: Icehouse

Post Number: 318
Registered: 02-2003
Posted on Saturday, August 21, 2004 - 02:20 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Dan-

I agree. I'm not talking about some software that predicts FG or anything like that. I was going off of White Labs website when it says "attenuation: 73 to 80%". Now, I would guess that if you mashed at a higher temp, or added dextrin malt etc, you would end up at the lower range of that yeast... around 73%. If you mashed at a lower temp, I would assume you would get near the top of that for 80%. I think I've gotten up to about 83% before with WLP001. But, I just don't see how 87% is attainable. I just must be missing something.

I just did a American Wheat with 10lb Wheat malt, 1 lb Rye, 1lb Munich, and 9 pounds 2 row. I mashed at 153, and hit my mash temp DEAD ON for 60 mins. You would think this would be a very fermentable wort, yes? I pitched a 2 Litre starter in a 10 gallon batch. Fermentation took right off! My OG was 1.056 and my FG was 1.013. I would've liked to have gotten down to about 10, but oh well. My point is, that is a 77% attenuation rate, and I just can't see getting another 10 percentage point.

Well, I've rambled enough....
 

Dan Listermann
Intermediate Member
Username: Listermann

Post Number: 369
Registered: 03-2004
Posted on Saturday, August 21, 2004 - 03:31 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Chad you still missed my main point. Published attenuation are a relative matter I suppose based on some "standard" wort. The wort make up is far and away the primary determinant of attenuation. Yeast is a poor second. If I throw a lot of corn sugar at a wort or let it mash a long time at low temperatures, I will get very high attenuation no matter what yeast or its published rate. A short high temperature mash will produce a low attenuation.

Really the producers of yeast need to switch to "low, medium or high" published attenuation rates. Putting numbers on it is misleading.
 

Brandon Dachel
Senior Member
Username: Brandon

Post Number: 1176
Registered: 03-2002
Posted on Saturday, August 21, 2004 - 04:27 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I kinda agree with Dan here. I think part of the confusion lies in that we tend to associate attenuation rates *directly* with the OG of the wort. The OG of the wort is strictly the specific gravity, nothing less/nothing more. It doesn't directly measure fermentability. And attenuation is a rate of fermentability. I can get to 1.050 with pure sugar. And that's alot more fermentable than a mash @ 158F. Now which one is going to finish closer to 1.010 with a yeast rated 72-78%?
 

Fredrik
Senior Member
Username: Fredrik

Post Number: 1516
Registered: 03-2003
Posted on Saturday, August 21, 2004 - 07:21 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I definitely agree with Dan. To take the published attenuation numners right off the manufactures homepage and use them to estimate the FG of an arbitrary receipe makes little sense. It makes sense, only if you have a wort that pretty much conicides with the "standard wort". As a thought experiment, what do you think would happend if you made a wort out of pure sucrose? About any strain would give you pretty much 100% *real* attenuation.

Personally I am sure the yeast manufacturer could do better if they only wanted to. I send them an email almost a year ago but they didn't bother answer it. If noone asks for it, why should they spend time on improving anything? Lets start mailing these guys and asks them to define their terminology. The ratings are cleary for some standard worts and standard pitching rates etc. Why not declare the conditions se we could make sense out of the numbers? Personally I have made some assuptions as to what these standard worts are, and tried to translate the manufacturers table into the strains ability to deplete maltotriose.

For practical purposes, with sensible pitching rates, glucose, fructose, sucrose and maltose are more or less (except some very minor residues) wiped out from the wort by about any strain. The difference between strains that explains their difference attenuations are concerned with their ability to ferment maltotriose. ALL S.Cerevisae has the genes to do so, but the difference is that these genes are expressed to different levels. Some strains practially wipe out all the maltotriose too, while some leaves almost all of it.

This means that the strain to strain variation in attenuation modulates the residual maltotriose levels only. The mashing scheme used affects not only the potential fermentability, it also affects the % of maltotriose in the wort (as well as the entire sugar profile). From what I've seen the maltotriose contents in extract ranges from some 9 - 16%. More beta-amyalase activity favours lower maltotriose levels.

A the point would be that the strain to strain variation has an upperbound in the maltotriose contents. In a wort with 0% maltotriose, for all ballpark estimates all strains would have exactly the same attenuation.

Another thing: I think real attenuation is less confusion. The only good thing with apparent attenuation is that it's easier to calculate, but it is a more confusing concept.

The best you can do fairly easy is as follows (this is what I do)

1. Inspect the manufacturers table and estimate the strains relative attenation power on maltotriose. The strains on the high end obviously ferment out maltotriose alot, and the low end may leave most or much.

2. Estimate for your wort
a) potential fermentability (g+f+s+m+mt)in %
b) maltotriose contents in %

I do this in my receipe sheet, I am lazy so I often used ballpark values for maltotriose levels in wort of around 10%, then I modulate this if I add sucrose. But I will improve this later.

3) Your real attenuation will then be the "potential fermentability - x * maltotriosecontents", where x=0..100% depends on the strain. x is the level of residual maltotriose.

Things are not exactly as easy as I suggest, and it's not perfect but it's a much more reliable way of doing ballpark estimates than to use the attenuation numbers right off.

/Fredrik

(Message edited by fredrik on August 21, 2004)
 

Bill Pierce
Moderator
Username: Billpierce

Post Number: 309
Registered: 01-2002
Posted on Saturday, August 21, 2004 - 12:40 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

As everyone has mentioned, there are a lot of variables affecting fermentability, attenuation and final gravity. Still, the published attenuation specifications for yeast strains seem reasonably accurate as general guidelines. For example, I predict if you mashed a grist of 85-90 percent two-row pale malt and the remainder of specialty malts, used a grain/water ratio of about 1.25 lbs. per gallon, had a mash pH between 5.2 and 5.6, converted for 60 minutes at 152 F, achieved 5 gallons of wort with an O.G. of 1.048, aerated the wort, pitched 150-250 billion healthy cells of Wyeast 1056 and fermented at 68 F, the apparent attenuation would be very close to 75 percent and the F.G. would be right around 1.012.

Of course the more you deviate from the "average" the greater the variability will be.

(Message edited by BillPierce on August 21, 2004)
 

Fredrik
Senior Member
Username: Fredrik

Post Number: 1519
Registered: 03-2003
Posted on Sunday, August 22, 2004 - 07:59 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I kind of agree with Bill and the others here, I just though I'd post some more details.

But beware this is alot of my personal speculation, but FWIW, my assuption (lacking definite info) of Wyeast standard worts is something like this ~

OG 1.0401-1.045
Extract fermentability 65% RDF
Maltotriose contents of extract 10.5%

This translates maltotriose depletion to the typically attenuation ratings as follows

80% apparent attenuation <=> 100% maltotriose depletion
67% apparent attenuatoin <=> 0%

Thus when I read wyeast tables I personally prefer to interpret their tables like this

WY3787 is rated 75%-80% => 62%-100% maltotriose depletion
WY1332 is rate 67%-71% => 0%- 30% maltotriose depletion

I suspect the variation within the same strain depends on stress influenced by for example pitching rate, aeration, CO2 pressure at EOF (ie rousing will reduce the stress near EOF). As many things are stressful at EOF, CO2 pressure may be what pushes some strains over the edge. Some strains may have large O2 requirements.

This way it is quite straightforward to translate the ranges to an arbitrary wort. It remains to find out the influence of CO2, and pitching rate this may be quite complicated. I hope to be able to dig into this more when the model is in operation. Right now, it's too complex to estimate all these things in interaction. This is as far as I can do ballpark estimates without the completed model. I think the model will eventually bring alot more power to these estimates (it would still be estimates).

White labs may have another standard wort, but it could be estimate as well. I haven't bothered as my LHBS only carry Wyeast.

/Fredrik
 

Fredrik
Senior Member
Username: Fredrik

Post Number: 1520
Registered: 03-2003
Posted on Monday, August 23, 2004 - 12:51 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Here is an example of a simple visual ballpark attenuation range translator. The OG has less impact, which is of the order of less than half a point from 1.040 to 1.060, the major difference is wort RDF.



The lines represent constant maltotriose depletion in % raning from 0% to 100% in steps of 10%.

/Fredrik
 

David Woods
Intermediate Member
Username: Beericon

Post Number: 371
Registered: 02-2003
Posted on Monday, August 23, 2004 - 04:51 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

How much does the pitching rate of any yeast effect the FG. Or over pitching(I know it near impossible, but I mean more than most people would pitch)?

According to Fredrik, there is only so much fermentables in a specified wort, so by that no matter how much you pitch the yeast can only convert so much starch to alcohol and CO2, correct?

Wow, homebrewing is so simple, and yet so complicated.

David
Onslo: "Get me a beer!"
Daisy: "We're out of beer."
Onslo: "I can't believe it! I'm completely surrounded by NO BEER!"
 

Bill Pierce
Moderator
Username: Billpierce

Post Number: 330
Registered: 01-2002
Posted on Monday, August 23, 2004 - 05:11 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Underpitching, as well as lack of oxygen (or pre-loaded sterols), clearly can affect attenuation. Yeast are limited in their ability to reproduce, and overstressed yeast does a poor job of metabolizing the sugars in the wort. There are also problems associated with overpitching, but it takes a considerable population, much more than can be pitched easily in a homebrew situation. My general experience is that pitching rates at least close (50-200 percent) to the "classic" of 1 million cells per milliliter per degree Plato will result in "normal" attenuation. I doubt that it's possible to precisely quantify the difference between 75 percent and 150 percent, for example, and I'm not sure it would be pronounced, anyway. Moreover, as has been mentioned repeatedly in this thread, there are a number of other important variables involved. I half admire and half scoff at Fredrik's attempts to model fermentation.

(Message edited by BillPierce on August 23, 2004)
 

Hophead
Advanced Member
Username: Hophead

Post Number: 946
Registered: 03-2002
Posted on Monday, August 23, 2004 - 05:44 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

"I half admire and half scoff at Fredrik's attempts to model fermentation."

I'd have to say I'm about 25/75... :-)

Chad, I like my beer on the 'drier' side, and typically finish at 1.010 or below, even with 1.070+ beers, using WLP yeasts. I make a starter, aerate, and typically mash ~150. Take the attenuation numbers as a way of comparing the individual yeast strains to each other, as has been said. 2 of my favorites, english and dry english, are great examples of how they will finish in relation to each other given the same wort and conditions.

Prost!
 

Fredrik
Senior Member
Username: Fredrik

Post Number: 1522
Registered: 03-2003
Posted on Monday, August 23, 2004 - 05:48 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

David, there is definitely a hard set upper limit to the fermentability determined by the mashing and grainbill. You'll hit that limit by a forced fermentation procedure using an attenuative strain, and there is no way you can violate this by any strain. This set upper limit may be a little higher for some lager or champagne strains though, but I consider them special cases, also the sugars relevant to those strains I think are not very significant in beer wort?

The low limit is softer, as it's obvious that due to various problems you can have a batch stuck at any gravity. But the softer lower limit is I think farily well defined too, for any "reasonable" fermentation performance. There may be some strains wich are exceptions but I would think that for all practical purposes this lover limit is when the fructose, glucose, sucrose and maltose are wiped out from the wort. This is the lower bound. Any fermentation that leaves significant amount of maltose must be (with exception of some in theory possibly very odd strains) seriouly flawed for some reason.

The impact of the other factors I think are quite difficult :-) and requires more testing!! wohoo :-) And I suspect these dependences will be even more strain specific. But by assumption the variation (within reasonable limits) is 0% - 100% maltotriose depletion. If you pitch so little yeast that you leave significant amounts of say maltose, then I think the pitching rate or something else must be way off. I'd guess some factors highest on the list is pitching rate, aeration, CO2 saturation, alcohol tolerance. Some of these are related though, pitching rate and aeration significantly affects alcohol tolerance.

I would like to make some pitching rate test, and also CO2 pressure tests. I suspect a continously stirred fermentation would give a significantly higher attenuation too. Has anyone used a stirbar in a fermenting carboy? results?

/Fredrik
 

Fredrik
Senior Member
Username: Fredrik

Post Number: 1523
Registered: 03-2003
Posted on Monday, August 23, 2004 - 05:54 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

"I half admire and half scoff at Fredrik's attempts to model fermentation."

You have all reasons to be sceptic, the more I've learnt the harder it gets :-) I just decided to give these 10um creatures a good game at least. I'm not going to let them fool me, I'm tracking their farts at least, they can not get away.

/Fredrik
 

davidw
Advanced Member
Username: Davidw

Post Number: 630
Registered: 03-2001
Posted on Monday, August 23, 2004 - 06:31 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

No worries, Fredrik. Some of us like to build equipment, others prefer to mimic guidelines to shine in competitions, you like to model various aspects of brewing. Rock on, dude.
 

David Woods
Intermediate Member
Username: Beericon

Post Number: 373
Registered: 02-2003
Posted on Tuesday, August 24, 2004 - 01:46 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I'm not going to let them fool me, I'm tracking their farts at least, they can not get away.

Fredrik, I somehow invisioned you screeming that as two guys with white suits chase you down the street!

David
Onslo: "Get me a beer!"
Daisy: "We're out of beer."
Onslo: "I can't believe it! I'm completely surrounded by NO BEER!"
 

Fredrik
Senior Member
Username: Fredrik

Post Number: 1525
Registered: 03-2003
Posted on Tuesday, August 24, 2004 - 05:39 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I have no other preferences other than consistency :-)

/Fredrik