Wednesday, February 24, 2016

THE ACTUAL TRUTH ABOUT YEAST: Volume 2 Ale Yeast with Kevin Lane of Fermentis

Today we continue our series with Kevin Lane of Fermentis, and we are focused on Ale yeast.   We will be taking a basic look at Ale yeast biology, understanding some of the terms you hear associated with ale yeast, and talking about how to get the flavors you want from ale yeast.  Any thing in italics I added, or clarified.  

We will gain an understanding that temperature, pH, pitch rate, and wort composition are tools you can use to make the beer you want.  And this is a very important point.  Too often now on home brewing forums I hear guys espousing "rules" ... "you have to do this"  or "you must do that"   To me, it is clear that these guys do not want to understand, they want to follow a set of rules that will make them successful.  Unfortunately, true success requires understanding.   My old mentor used to say "Recipes are for people who can't, or wont understand"  I finally get what he meant.  He would check gravities during the mash, and add base grain.  He would check color against a chart and cap his mash with crystal grains.  He would even check pH and see if it was optimum for the fermentation phase.  All because he understood the process and enough of the microbiology to make the adjustments. 

Yes this is a long post,  but read it. 
This is the stuff you actually need to know!

And always remember,  Brewers make wort, yeast makes beer!

What is ale yeast?  What makes it different from lager yeast?

Ale yeast is defined as top fermenting yeast.  Ale yeast (saccharomyces cerevisiae)  is a different species from lager yeast (saccharomyces carlsbergensis (former} orpastorianus {current}). Ale yeast, also prefers to ferment at warmer (usually ambient) temperatures, whereas lager yeast prefers to ferment at cooler temperatures.  The yeasts don’t actually prefer one over the other, they just produce better flavors/aromas and may ferment “better” in human terms.  Ale yeast, additionally, has a much larger variety of flavor and aroma production, as lager yeast has been selected by humans for centuries and has been (intentionally)  limited in the genetic differences.  There are a large number of different ale yeasts available in the market: American, English, German, Belgian, French, etc.

So top cropping versus bottom cropping? (Taking yeast from active fermentation)

When you choose whether to top crop or bottom crop, you are selecting different phenotypes (genetic differences).  If you top crop, you will be selecting the yeast that is more likely to form branched groups of cells that get stuck in the krausen during fermentation.  Traditionally, German ales have been top cropped for many styles, but the most common is hefeweizens.  If you were to top crop and bottom crop from the same batch of beer (separately) and repitch into the next batch (separately), you would likely see a difference in flavor/aroma production.

Why can ale yeast perform at higher temperatures?

Ale yeast performs better at higher temperatures.  That isn’t to say that you can’t use lager yeast at higher temperatures (ex. W-34/70 at warmer temperatures); you can, there is just higher potential for off flavor development (sulfurs, meaty notes, cider type flavors, etc).  Ale yeast are and have been naturally occurring yeast strains in regions that have warmer typical temperatures.  There are different stories about lager yeast and where that genus species came from, but my understanding is that lager yeast is a decedent from a cross between wine yeast (beyanus) and ale brewing yeast.  Wines are typically produced in coastal regions where the overnight temperatures drop to a fairly cool temperature with moderate humidity, so I could understand how lager yeasts could be a decedent of saccharomyces beyanus (wine yeast). Wine is also typically fermented at cooler temperatures when compared to ale yeast, so the cross between the two species is understandable: the maltose and maltotriose fermentation coming from the cerevisiae and the affinity for cooler temperatures from beyanus.

Back to the question, ale yeast performs better at higher temperature because that is how the environment was that the yeast came from.  Again, it’s not to say that ale yeasts definitely can’t ferment at cooler temperatures, they can, just might be slower and produce more neutral beer (ex. K-97 at cooler temperatures).

What impact, in general, does temperature have on fermentation and production of flavors?

Fermentation temperature is an “environmental condition” similar to OG, pH, pressure, pitch rate, etc.  In general, warmer temperatures will increase fermentation speed, increase ester production, and increase overall yeast flavors.  At cooler temperatures, yeast produce a more neutral beer, in general. 

This image shows the Safbrew WB-06 speed of fermentation (drop in degrees Plato) over time at three different fermentation temperatures: 16, 20, and 24°C (60.8, 68 and 75.2°F).  As you can see, the 16°C fermentation takes 6 days longer than the 24°C!

What I think is interesting is that different strains perform different ways.  Here is an image of how one of the Fermentis strains, Safbrew WB-06, performs in cooler temperatures, where it produces more isoamyl acetate (banana flavor).

Unfortunately (and fortunately for us as brewers), there are these differences between strains, where some will produce more of a certain chemical at lower temperatures, where others will produce more at higher temperatures.  Generally speaking though, yeast will produce more flavor compounds at higher temperatures.

What are the flavors produced by ale yeast?  

Ale yeast produce a wide variety of flavor and aroma compounds.  It is important to remember that the yeast is producing these compounds to develop the aroma and flavor in beer, they are simply just living in the environment that the brewer puts them into and most flavor and aroma compounds can be related to the stress of the yeast.  If you read the first installment of this Q&A with David and I and you took the time to look at that HUGE pdf image that I had him put in, you will see hundreds of compounds produced and altered by the yeast.  Each of those will have a different flavor and aroma and more importantly, a different human threshold.

The main flavors that brewers care/think about are phenolics (covered in the last installment of this), alcohols, and esters. 

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

Esters are generally created in stressful environments.  Esters are actually a compound that is formed by the yeast or simply by accidently being bound in the aging beer.  It is the combination of different alcohols and carboxylic acids.  More esters are generally produced in warm fermentations, wort with low dissolved oxygen (Acetal CoA can be in excess in low O2 environments), lower pitch rates (more cell growth), and tall thin fermenters.  Generally, less esters are produced with an increased fermenter pressure.  It is also important to understand the different human threshold levels (ex. isoamyl acetate has a human threshold of 1.4ppm while ethyl acetate has a human threshold of 33ppm).

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

In general, if you want to create a more neutral beer (low ester), you would over pitch slightly, keep the fermentation cooler than usual and if possible, keep some back pressure on the fermentation (not easy for home brewers, I know).  In addition, strain selection is important.  If a strain is more likely to produce esters in comparison to another, obviously, choose the low ester producer.  The same can be said about higher (superior) alcohols.

If a brewer wants to enhance these flavors (esters) what advice would you give?

Basically… the opposite of what I said above.  Choose a strain that is known to produce a lot of esters and higher (superior) alcohols.  Ferment warm, with a low pitch rate and little back pressure.

You have all been told that esters are bad, esters are neither bad or good, they are a tool for you to shape and create the beer you want.  Some fruity ale esters are important in many English beers, and in american , IPA, DIPAs, Belgians, and German Wheat beers

Ale yeast can also produce Phenolic flavors... Belgian flavors how does a brewer enhance these flavors?

The best ways to increase the phenolic flavor in beer is ingredient selection and strain selection.  In order for the yeast to produce phenolic flavors, they need the precursors (ex. ferrulic acid for 4-vinyl-guaiacol {4-VG}) and the yeast need the POF+ (phenolic off flavor positive) phenotype.  Some strains have that and others do not.

The malts that are highest in ferrulic acid are wheat malts.  In addition to the malt having that compound, the brewer can use step mashing to promote the extraction from the ingredients.  The rest that you will want for the ferrulic acid would be somewhere around 109-113°F.

So practically, to make a great abbey style ale, you need some wheat and you need to step mash?

Yes, and you need a yeast that has the POF+ phenotype.  Now, I have to make a comment that maltsters, currently, are doing a great job at modifying the malt, so the step mash isn’t completely necessary… it just is if you want to increase the phenolic expression by the yeast.

Are there specific sugars that ale yeast doesn't digest?   And how can brewers know what malts are high in these sugars?   

There is a specific group of sugars that ale yeast (typically) won’t ferment: dextrins.  Dextrins are a group of complex carbohydrates that most yeast are unable to pass across their membranes.  There are malts that are named specifically dextrin malt.  Some are hidden in the name (ex. "Carapils"). 

So wort composition is important?

Wort compositions is very important. 

When looking at the visualization above, it is easy to see that there is a portion of the mash that is not fermentable.  This depiction also includes the proteins and other compounds, but the idea is there,  generally for malt derived wort, only 70% of what you are extracting during your mash and lauter is fermentable.  The dextrins can be made fermentable with enzyme additions, but that isn’t something that most homebrewers are looking into doing. 

Do you think there is too much focus by the majority of brewers on limiting ester flavors"?  in other words do you think many brewers now think of any esters flavors in beer?

I think that it depends on the beer style you are trying to make.  Obviously, there are certain styles that you don’t want esters in, but there are others that you want a lot of esters in (Belgian styles usually have higher amounts of esters).  What I have been promoting in the last decade is, it doesn’t matter if your beer fits a certain style guideline or if it doesn’t.  usually, you are making the beer for yourself and your friends and in that way, you should make whatever type of beer you want to: low or high ester amounts.  If you are looking to enter a competition, then I would say, try to follow what the BJCP says; after all, the BJCP was created for homebrew competitions and it clearly states that in the opening of the document.

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

There are simply too many to list and how to limit them all. 

I will cover the big ones here but most can be limited by thinking about the stress level of the yeast:

Cidery notes – generally can be explained as a lack of yeast nutrition due to adjunct addition – avoid by decreasing the amount of adjunct or addition of a complex yeast nutrient (not just DAP) (Diammonium Phosphate)

Excess sulfur – generally due to autolysis – avoid by moving the beer to secondary after fermentation slows/ends

Meaty notes – partially or fully autolyzed yeast – avoid by moving the beer to secondary after fermentation slows/ends or make sure the alcohol level isn’t too high (alcohol degrades cells)

Aldehydes – produced naturally during fermentation and are later reabsorbed by yeast – allow the beer to be in contact with yeast for more time

Diacetyl (vicinal diketones {VDK}) – produced naturally during the growth phase by yeast due to the lack of Valine and Isoleucine (amino acids) and is a byproduct of the yeast synthesis of these two amino acids.  Yeast will naturally absorb and assimilate this after the sugar fermentation, however it is also produced by bacteria and if you have an infection, the yeast will never be able to assimilate it all.

Soapy notes – fatty acid degradation and dead or inactive yeast degradation – avoid by moving the beer off the yeast, especially if it is a high alcohol environment

Note:  Having the yeast in contact with the beer for long periods of time is rarely a problem in home brewing.   In home brewing we are generally not dealing with amounts of yeast that can harm our beer.  But when you are brewing a huge OG beer, or adding fruit, wood, spices etc... you might consider secondary fermentation.

What general advice would you give new and intermediate brewers about brewing an ale?

Ale fermentation is the most common for home brewers because it doesn’t necessarily require any extra equipment for cooling the fermentation.  Remember that yeast do produce heat as a byproduct of fermentation, so fermenters will heat up in high fermentation.  In general, ales are more forgiving, so the brewer doesn’t need to have an exact fermentation temperature.  Additionally, understand that there are a lot more flavors in beer than just the yeast.  Malts, hops, water and adjuncts all contribute something to the flavor of the beer and understanding all of those as well will help you make the best beer you have ever made.  Yeast is the most complex part of the beer, because it is (usually) the one living part of the beer; the hops have been harvested off the bine and the barley has been harvested and malted.  For brewing ales, I always suggest to start with the suppliers guidelines and then experiment from there as it will give you a baseline and starting point (ex. Fermentis produces the 11.5g sachets for 5 US gallons of beer, but you could always use more or less to find out what happens).  We also recommend a temperature range, but you can ferment above or below that.  That is the exciting part of homebrewing to me… you can do whatever you want and make it completely your own!


  1. This comment has been removed by a blog administrator.

  2. Really insightful post. The yeast part of brewing is so complicated but this helps build a foundation and an idea to move forward with. Thanks

  3. Very good article.

    As a general 'rule of thumb', when do we move the beer to the secondary fermenter? And for a medium OG of say 1.04, what is the maximum time on only the primary yeast (1 week, 1 month, 3 months)?

    1. Johan, that will be asked in our next episode on lager yeast. I would say, I have safely left beer on yeast for 2 months with no ill effects. But I will ask.

  4. This is incredibly insightful. Please thank Mr. Lane for sponsoring this article with you! Looking forward to part three....

    1. This comment has been removed by the author.

  5. You said, "Safbrew WB-06, performs in cooler temperatures, where it produces more isoamyl acetate (banana flavor)."

    This is the product card for Fermentis Safbrew WB-06

    It says, "for clover flavors : below 22°C (71.6°F)
    for banana flavor: above 23°C (73.4°F)"

    I am confused!

  6. Im aware. It was confusing to me too. But that is recent research. I am looking forward to trying it out myself soon.