THE ACTUAL TRUTH ABOUT YEAST: Volume 3: Lager yeast, with Kevin Lane of Fermentis.

the world's most popular lager
yeast. Good ol' 34/70

Part 3 in our on going series about the little bugs we all love.  This time we are focused on lager yeast with Kevin Lane of Fermentis.  And this one is great.   In our next installment we will be talking all about sours.... yum!

What is lager yeast?  

Lager yeast is a yeast that is generally used for producing cool fermentations (to be discussed later).  It is often referred to as a bottom fermenting yeast, due to the fact that it ferments from the bottom of the tank rather than the top, as ale yeast does.  Lager beer is also, typically, stored cold (lagered) for a period of time before being packaged/sold to the consumer or consumed. 

The species itself, Saccharomyces pastorianus, is believed to be a descendent/hybrid of Saccharomyces eubayanus.  Lager yeast has been named multiple names in the past, most recentlySaccharomyces carlsbergenesis, after the Carlsberg brewery, but is now defunct nomenclature.   

What makes it different from ale yeast?

The easiest way to explain the difference (which isn’t easy at all) is that it is genetically different.  So much so, that it is categorized as a different species of yeast Saccharomyces pastorianus. The brewer typically doesn’t think about that when brewing, but that is the real difference.  The genetic difference influences the brewer to use lager yeast in cooler fermentations and for certain styles of beer, where you are looking (generally) for less flavor impact coming from the yeast.  Lager yeast strains are very similar to one another and do not produce as wide a flavor range as ale strains do (think English ales vs Belgian ales).  Typically, lager yeast will attenuate fairly well and produce a very clean, crisp beer.

What is meant by bottom cropping?

Bottom cropping is a term that has been created to explain the process of collecting the yeast from the bottom of the tank.  Since lager yeast ferment at the bottom, you have a higher likelihood that you will be collecting healthy yeast from the bottom.  This is not to say that you cannot do the same with ale yeast; you certainly can, you just run a higher risk of collecting less healthy yeast cultures.  In ale yeast re-pitching, brewers traditionally would top crop and collect the krausen.  Thus, when lager beer production really picked up… the brewers came up with a new term and a new way to collect.

Why can lager yeast perform at lower temperatures?

Why not?

… I am kidding. 

Lager yeast produce the flavors that the brewers want at lower temperatures because of the genetics.  It is difficult to explain because people have talked about the characteristics of the yeast as what they do for the brewer, not what they do as an organism.  I think I may have stated this before but I will repeat… yeast don’t ferment wort to make beer, they don’t ferment must to make wine and they don’t ferment apply juice to make hard cider nor do they ferment mash to make the base for distillates.  All that yeast is doing is attempting to survive and reproduce so that their genetics are passed on to their daughters and subsequent generations. 

So, to get back to your question, yeast perform (the way the brewer wants it to) in certain environmental conditions, simply because of the genetics

Will Lager yeast work at higher temperatures?

It depends.  Some of the strains will work at higher temperatures and others will struggle.  I guess the real answer is yes, they will.  But the more complete answer is, yes, they will but they may not successfully finish the fermentation and could produce some flavors that are unwanted. 

Some yeast strains are capable of the same fermentation characteristics at lager (low) and ale (high) temperatures.  There is a lot of research that Fermentis is currently involved with, to bring these answers to you more definitively.

So it will ferment, but it will put off some off flavors?

Yes, the yeast will ferment.  There is a higher possibility for the yeast to produce unwanted flavors.

What are the flavors produced by lager yeast?  

Lager yeast will produce a lot of the same flavors that ale strains will, just in lesser amounts.  Typically, lager yeast will produce the same ester profile as ale strains, just in low enough concentrations that humans either don’t detect it (below the flavor threshold) or just slightly detect it.  Typically, lager yeast are POF- (phenolic off flavor negative) and will not produce the flavor complexities that are common in some Belgian and German beers. 

Typical ester production would include ethyl acetate (apple), isoamyl actetate (banana), ethyl hexanoate (tropical fruit), etc.

 So it still produces esters, just different esters than ale yeast?

ester forms naturally in fermentation.

The difference in the ester production isn’t the molecules that the yeast are producing but rather the concentrations and ratios of one to the others.  This will develop the differing characteristics in the beers and in a way the styles that lager yeast is used in.  Due to the fact that esters are combinations of organic acids and alcohols, the elevated levels in ales could also be perceived as a harsher beer, compared to the delicate profile of lagers.

What causes lager yeast to produce more or less of these esters?

The best way to think about this is the principle of mass conservation: nothing can ever be created or destroyed. The reason I say that is the best way to think about it is because esters are produced from different alcohols and organic acids.  If the yeast is in cooler temperatures and there is a higher pitch rate (general characteristics of lager production), the yeast will be less stressed and thus produce less of the variety of alcohols and acids.  With less of the “building blocks” available, less of the esters will be produced.

So stress and temperature have an impact, but what about pitch rate?

Pitch rate can be thought of as another environmental condition, in a way.  If there is a higher concentration of cells in the wort at pitching, the yeast will be less stressed to reproduce to build the correct concentrations.  Essentially, all of the flavors and all of the characteristics of the yeast come back to stress levels. 

If a brewer wants to make extremely "clean" lager with very little ester, what advice would you give him or her?

There are a couple of things the brewer can do, but I don’t know the application ability.  There are a couple of things that are easy to apply to make beer more “clean”, as well.  The easy applications are lower temperatures and higher pitch rates.  If the brewer has temperature control and are able to ferment in the upper 40’s, the lager yeast will produce a very neutral flavor.  Likewise, the brewer can also pitch at elevated pitch rates, nearing 200g/hL or roughly 4 x 11.5g sachets of Fermentis lager yeast (some other producers have differing viability and pitch rates, so I can’t speak for them).

Practically speaking if you want to make lagers, you have
to be able to control fermentation temperatures. 

The difficult aspects to change about the fermentation would be to increase the back pressure on the fermenter.  This can be done with most any pressure release valves connected to the fermenters blow off port.  The other important thing to remember is you don’t want to build a “bomb”, so you need to make sure your fermenter is capable of holding back pressure.  Not easily done, but will increase the neutrality.

   

So practically, to make a great lager you need to ferment cold?

To make a great lager, it is strongly recommended to ferment cold.  It doesn’t mean that you can’t make a great lager at elevated temperatures, but it is much easier to do so at lower temps.  Yeast will act according to what you do to them.  If brewers know that lager type flavors are produced (or not produced) at lower temperatures, then I would suggest that you apply that to the lager fermentation.

Are there sugars that lager yeast can process that ale yeast cannot process?

No… well… it depends on what strains you are comparing.  Lager yeast typically will ferment maltotriose to near completion.  Some ale strains will ferment maltotriose to completion while others will hardly touch it, if at all.  The important thing for the brewer is to understand the capabilities of the yeast they are using and apply the correct environment to allow the yeast to produce the beer that the brewer wants.

 So wort composition is important?

Wort composition is always important.  I cannot say it enough, “Brewers don’t actually make beer.  They make wort.  Yeast make beer.  If yeast don’t have what they need, they won’t do what you expect.”

 What unwanted off flavors can lager yeast produce?   and how do you limit them?

The most common off flavors are sulfurs, meaty notes and other internal yeast component release.  Most of these are caused by time and temperature, but can also be caused by lack of nutrition, in some cases.  If you are attempting to make an American Light Lager (very difficult), there is a need to supplement nutrition for the adjunct addition.  Adjuncts will not bring any nutritional components other than carbohydrates (food).  Yeast will need the mineral and vitamin cocktail that malt brings to the table (plus a little Zn and Mn). 

What general advice would you give new and intermediate brewers about brewing a lager?

General advice: make mistakes and learn.  It is a much different practice brewing lagers and the best results come from paying complete attention to the brew.  Since I spent 5 years of my life as a Pilot Brewer at one of the big guys, I have a bit of experience with lager brewing.  I can say that it is a very difficult range of beer styles to master.  The fermentation is one aspect of it that, in particular, needs to be done right.