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Home Brew Forums > Home Brewing Beer > Brew Science > Ale vs. Lager Yeast
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Old 03-07-2009, 02:29 AM   #1
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Default Ale vs. Lager Yeast

What is the difference between lager and ale yeasts? Not that one is top fermenting and one is bottom fermenting. What do they do differently, chemically?

I was told this by Ray McNeill, but being totally inebriated by much good homebrew and microbrew, I can never remember.

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Old 03-07-2009, 03:46 PM   #2
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Well, in short they are of the same genus, but different species. This essentially means that they are closely related, but not too closely, i.e., they have slightly different DNA, morphology (form/structure) and other characteristics.

Ale yeasts are easy. They are simply Saccharomyces cerevisiae.

The taxonomy of lager yeasts seems to be changing over time by scientists. It started out being called Saccharomyces carlsbergensis. Since then lager yeasts have been referred to as Saccharomyces uvarum, Saccharomyces cerevisiae vars uvarum, and Saccharomyces pastorianus.

For simplicity, lager yeasts can be broken down into 2 species: S. uvarum and S. pastorianus. They are both believed to be hybrids:

S. uvarum = S. cerevisiae + S. monacensis
S. pastorianus = S. cerevisiae + S. bayanus

Lager yeasts can metabolize at cooler temperatures than ale yeasts. Correspondingly, they can undergo stress at cooler temperatures than ale yeasts. Lager yeasts also produce different proportions of flavor-active compounds than ale yeasts (sulfur compounds and diacetyl are 2 good examples). Lager yeasts don't bind together as nicely as ale yeast. Therefore, they form smaller colonies and a smaller krausen. The can also ferment a few more sugars than ale yeasts. Ale yeasts cannot ferment melibiose, but lager yeasts can. Ale yeasts can partially ferment raffinose, but lager yeasts can fully ferment raffinose. However, since the quantity of these sugars in wort is so low, it's rarely a noticeable increase in attenuation.

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Old 03-09-2009, 06:46 PM   #3
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Quote:
Originally Posted by menschmaschine View Post
Well, in short they are of the same genus, but different species. This essentially means that they are closely related, but not too closely, i.e., they have slightly different DNA, morphology (form/structure) and other characteristics.

Ale yeasts are easy. They are simply Saccharomyces cerevisiae.

The taxonomy of lager yeasts seems to be changing over time by scientists. It started out being called Saccharomyces carlsbergensis. Since then lager yeasts have been referred to as Saccharomyces uvarum, Saccharomyces cerevisiae vars uvarum, and Saccharomyces pastorianus.

For simplicity, lager yeasts can be broken down into 2 species: S. uvarum and S. pastorianus. They are both believed to be hybrids:

S. uvarum = S. cerevisiae + S. monacensis
S. pastorianus = S. cerevisiae + S. bayanus

Lager yeasts can metabolize at cooler temperatures than ale yeasts. Correspondingly, they can undergo stress at cooler temperatures than ale yeasts. Lager yeasts also produce different proportions of flavor-active compounds than ale yeasts (sulfur compounds and diacetyl are 2 good examples). Lager yeasts don't bind together as nicely as ale yeast. Therefore, they form smaller colonies and a smaller krausen. The can also ferment a few more sugars than ale yeasts. Ale yeasts cannot ferment melibiose, but lager yeasts can. Ale yeasts can partially ferment raffinose, but lager yeasts can fully ferment raffinose. However, since the quantity of these sugars in wort is so low, it's rarely a noticeable increase in attenuation.
This is the best post I have seen yet on this forum.
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Old 03-09-2009, 08:38 PM   #4
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Ale yeasts tend to form colonies (distinct from flocculation) if the daughter cells don't separate from the mother. This causes them to rise to the top. Lager yeasts don't do that. Flocculation is different and there is no correlation between how flocculant a yeast is and how much yeast ends up in the Kraeusen since there are many poorly flocculating yeasts that are typical top fermenting yeast and also many highly flocculant yeasts that are typical bottom fermenting yeasts.

The taxonomy of the lager yeas is an interesting subject. Mensch, did you get the S. uvarum = S. cerevisiae + S. monacensis from the Briggs book?

It should be noted that ale and lager can metabolize the same major wort sugars and that their difference in metabolizing melibiose and raffinose (raffiniose is melibiose and fructose linked together) has no impact on the final attenuation since neither of them are contained in wort in appreciable amounts. It has already bee said, but I wanted to reiterate this here.

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Old 03-09-2009, 09:59 PM   #5
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The taxonomy of the lager yeas is an interesting subject. Mensch, did you get the S. uvarum = S. cerevisiae + S. monacensis from the Briggs book?
I can't remember for sure, but I think I got it here. And upon further reading, it may be that S. monacensis is a hybrid of S. pastorianus, rather than an ancestor as suggested here. (Tonedef you spoke too soon!)

That paper states that S. pastorianus and S. bayanus have a common ancestor, as opposed to S. uvarum and S. pastorianus like I stated. I'd have to read that paper a few times to understand the break-down better and don't have time right now. Let me know what you think, Kai.
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Old 03-11-2009, 03:01 AM   #6
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Here's some info from a book on yeast:

Quote:
The Saccharomyces sensu stricto group consists of S.
cerevisiae and three other closely related ‘sibling’ species S. bayanus, S. paradoxus and S. pastorianus. Although closely related, the four species split into two ‘clusters’
(Table 4.8) (Montrocher et al., 1998) consisting of (i) S. bayanus and S. pastorianus
and (ii) S. cerevisiae and S. paradoxus. The two clusters differ fundamentally in their
response to temperature. Compared to the ‘cerevisiae’ cluster, the ‘bayanus’ cluster
grows at a lower optimum and maximum temperature (see Section 4.2.3), is able
utilise melibiose (Naumov, 1996) and transports fructose via an active proton symport
(Rodrigues de Sousa et al., 1995). Despite these differences, it is worth noting
that although separated into clusters, the yeasts within the Saccharomyces sensu
stricto group consist of ‘very closely related yeasts when the whole genus Saccharomyces
is considered’ (Montrocher et al., 1998).
Also of note:
With the cerevisiae group fructose transport is facilitated rather than active.
S. cerevisiae is not considered naturally occuring because it is not found in any quantity in the wild.
"The generally accepted view (Martini, 1993) is that wine and
brewing strains of S. cerevisiae have evolved in industrial environments via selective
pressure through being better equipped to ferment grape musts and wort."


Also.. the taxonomy of yeast is damn confusing. I've read the Briggs book, and what menschmachine says goes along with that, but in my Brewing Yeast and Fermentation book (Boulton and Quain), they list the cerevisiae group as ale yeast and actualy ale fermentation being almost entirely S. cerevisiae with little S. paradoxus (which they list as an undomesticated yeast found in natural habitats such as broad leaved trees) and the bayanus group as the lager group consisting of S. bayanus and S. pastorianus. Which means that what Briggs said (S. pastorianus = S. cerevisiae + S. bayanus) cannot be true. And I tend to agree with Boulton and Quain on this as after reading through the chapter on taxonomy, yeast are not classified as a mixture of two different species(and I don't think anything is, that goes away from the classification system), rather the species and strain of that species.
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Old 03-11-2009, 02:27 PM   #7
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Quote:
Originally Posted by z987k View Post
And I tend to agree with Boulton and Quain on this as after reading through the chapter on taxonomy, yeast are not classified as a mixture of two different species(and I don't think anything is, that goes away from the classification system), rather the species and strain of that species.
Great info. The only thing I'll add is that I don't it's suggested that any yeasts are mixtures of other yeasts, but mere hybrids, kind of like a labradoodle.
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Old 03-11-2009, 09:56 PM   #8
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I read further last night (I haven't read a large portion of the book, it's 700 pages) and they end up concluding that they are hybrids, but end the end say the yeast taxonomy is so confusing and pointless to a brewer that they from that point on call all brewing yest S. cerevisiae and S. pastorianus for lager yeast when it is called for. All for simplicities sake, as like they said... it really doesn't matter.

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Old 03-12-2009, 09:23 AM   #9
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Also interesting, is EC-1118 - their campaign yeast is S. bayanus

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