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Brewers make wort,
Yeast makes Beer! |
The old adage is that
"brewers make wort, yeast makes beer" and that is true. Despite all of your best efforts you can not make beer with out the help of these miraculous little critters. Of all of the things we deal with as brewers, mashing, hop additions, water chemistry, chilling and dreaded off flavors, yeast is perhaps the least understood, and the most researched.
In truth you don't really have to understand yeast to make great beer. In truth you could never fully understand yeast. You can literally study it for your entire life and never learn all there is to know. Heck, they offer PhD's in yeast studies. What did you think a PhD in microbiology was?
But
to become a great brewer, to consistently make world class beer, you need to know at least the basics about yeast. So, I am teaming up with Kevin Lane of Fermentis. To do a three or four part series on yeast. The series will be presented as a question and answer format. It will have straight answers on yeast. Yes, it is from one of my trusted sponsors. Yes, it may have a decidedly "dry" yeast slant. But It will also have loads of good information. The first question and answer is called, "yeast basics".
Remember, a big aim here at Counterbrew is to dispel some of the common wisdom (read as misinformation) about home brew. With the growth of the internet, you can easily source all kinds of good information about home brewing. There are hundreds of articles available for free online that are credible and educational. Unfortunately, there is also so much bad information about brewing out there.
Much of that bad information is released by good, intelligent, caring people who are trying to show you all a "best practice". Not a Law of Brewing. Here are some examples of questionable information.
- The need to heavily aerate or oxygenate your wort.- they don't need as much as you think. You don't need 60 seconds of pure o2.
- The need to ferment lagers under 50 F (10 C) - I've used 34/70 for years at 62 F (16.66 C) No off flavors and several awards.
- The need to pitch a huge volume of yeast every time - sometimes you want stressed yeast. yes sometimes you want more off flavors.
So, to dispel some of the mis-information. We go straight to the source, Kevin Lane, Technical Sales Manager of Fermentis. Anything I added is italicized.
What is yeast?
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Louis Pasture the actual father of
modern brewing. |
Yeast is a microorganism that is part of the Kingdom Fungi. The Kingdom Fungi is a group of Eukaryotic organisms (membrane protected organelles) that have the ability to function as a unicellular organism. Yeast are not plants and are not animals or bacteria. They are similar to animals in the means of digesting food by absorbing and breaking down food to receive energy. Brewer’s yeast was discovered in 1876 (Louis Pasteur) and has been applied to brewing beer as a pure yeast strain selection since 1883.
What does yeast do?
Yeast survive. Their entire reason for doing what they do is to survive and to create new generations to succeed themselves! In their attempt to survive, they consume food (sugars) for energy and grow in population (by digesting proteins and amino acids as well as trace components). Their digestion of sugars creates alcohol, CO2, heat and other trace chemicals that we recognize as flavors and aromas. (trace chemicals are a small % of output, but huge impact on the flavor of your beer)
Why does yeast do what it does?
Yeast ferment (digest) to provide energy for themselves. The chemistry is very complex and the metabolic pathways for nearly every chemical the yeast produce has been mapped out. The easiest way to describe what the yeast is doing is by analyzing the ATP synthesis via their metabolic pathways. The real answer to why yeast does what they do is very simple: they live! They are living, breathing (in aerobic environments), eating and sexing (asexual) machines! (fungi not really machines)
What is a metabolic pathway?
A metabolic pathway is the means by which an organism metabolizes (processes) chemicals. For yeast, the metabolic pathways describe the breakdown of sugars, proteins and any other chemical compound that they transfer through their cell wall and digest. If you google yeast metabolism, you will find many visual diagrams, showing the many metabolic pathways
This is one of my favorite chemical pathway maps to show people. I received it from a good friend, Alex Combe, who I worked with in the pilot brewery at MillerCoors. It really shows how complex yeast are and how many different pathways they control for the production of different components. (very sciency and complex but if you want a pdf, let me know)
So yeast converts sugar to Alcohol, and CO2, and creates a range of other by products. What are these other by products?
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Do you really know how to prepare
a wort for real Belgian flavors? |
The other by-products are any of the intermediates in the diagram of the biochemical pathways. It can be said that most of the intermediates are only present for a short period of time, while the yeast are going through the biochemical pathways, but they are still present and therefore can be released from the cell, due to many factors. The main by products that we are brewers are concerned with impart flavor and aroma to the beer. With that said, the main focus is usually on esters and off flavors. It is important to note that certain flavor and aroma compounds (ex. 4VG {phenolic}) are only possible if the wort supplies the precursor (in 4VG production, the precursor is ferulic acid) and the yeast need to have the genentics to produce the compound (again with 4VG, the yeast need to carry the POF+ gene {phenolic off flavor positive}). (very important points made here, hop you all caught them... if you want a phenolic spicy Belgian beer better make sure you get ferulic acid in your wort... here's a hint you have to step mash!)
So the other by products of fermentation contribute a lot to the flavor of a beer. How can home brewers increase or decrease these by products?
There are many factors that can contribute to increased or decreased expression of the by products. There are simply too many to list and there are still some unknown factors that yeast producers/providers and Universities are investigating. The major contributors are: pitch rate, fermentation temperature, OG, pH, fermenter design (tall, narrow vs. short, wide), open fermentation, etc. The key to remember is that if you change one of those parameters, there is a chance that the yeast will perform differently. In the yeast world, we refer to these as environmental conditions and the brewer is there to attempt to create the environment that the yeast will perform best in. Most of the parameters come down to stressing the yeast (ex. if you under vs over pitch, if it is a cool environment or a hot environment. A metaphor could be made that yeast are very much like humans, in these regards: if you are stressed, bad words come out of your mouth (at least they do out of mine).
There is a lot of emphasis on the role of oxygen right now in home brewing, can you talk about that?
This is a very interesting topic. There is a lot of confusion in home brewing as to the needs and demands from yeast. Yeast need oxygen to produce sterols that are part of the cell. They need oxygen to reproduce and to live a healthy life.
That being said…
I can only speak for Fermentis and that is what my intention is here. Our yeast are produced in fully aerobic environments that have sugar and nutrients dosing. We propagate our yeast with the idea that we want the yeast to be as healthy as possible, when the brewer (whether home, craft or industrial) purchases it. We move immediately from propagation to the drying process, which is quite extensive (5 stages and each strain has a different recipe to make sure it remains in peak condition). With that, our dried, packaged yeast has enough sterols and oxygen demanding components to reproduce 10 times without any oxygen present in the wort! We have performed trials to analyze this and have the results. Does that mean you should try to make oxygen deprived wort? No. Does that mean that you don’t need to be concerned about the oxygen? To some extent. The idea that I want to get across here is that Fermentis provides you with a “safety blanket”. The yeast is already able to reproduce 10 fold, so there isn’t a need to be pumping a bunch of oxygen into your fermenter or being concerned about the DO levels. (basically quit stressing about Dissolved Oxygen, Shake it up, hit it with a little o2, use an aquarium pump, but don't obsess over the dissolved oxygen it will be fine RDWHAHB I should point out to you skeptics that Brulosophy has tested this misnomer.)
There is also a lot of emphasis in home brewing on proper pitch rate of yeast, how can a home brewer know they are pitching the right amount of yeast? Does Fermentis offer a calculator? Does Fermentis have a viable cells per sachet list or resource?
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Wort Rehydration of Fermentis
t598 and s33 |
Another very good, but difficult question to answer. The difficulty isn’t in the later questions; the difficulty is in the first question regarding “proper pitch rate”. I would like to remind you that yeast is not an ingredient, it is a living organism. With it being a living organism (and I will reference back to the question about by products), if you put the yeast into a different environment, they will act differently. Is there a proper pitch rate? My answer is no. The beauty of brewing is that you can change the flavor every time you brew and end up with different beers based on a few changes. The end results are up to the brewer’s opinion of what they want. If everyone reading this were to try the same 20 beers and list them from best to worst, we would likely all have a different order. Some beer drinkers like IPAs, some like Stouts, some like phenolic flavors and some hate phenolic flavors. It is important to remember that you as a home brewer, are able to create the beer that you want and that you think is the “bees knees”.
Back to the question, Fermentis recommends a pitch rate range: for ales we recommend 50-80g/hL(grams/hectoliter) and for lagers 80-120g/hL. Remember that a standard home brew batch of beer is just shy of 20L so we recommend 10-16g for ales and 16-24g for lagers. Does this mean that you need to stay within those recommendations? No, you get to do what you want! (important point here, you might pitch more or less yeast depending on what you are trying to accomplish)
The other tricky thing about this topic is that people have been hypnotized by liquid yeast, to the point that they always want to know cell count. For liquid, that is the best way for you to measure the amount of yeast you are adding. For dry yeast, we recommend a biomass pitch rate (weight/volume). If you read the bottom of our technical data sheets, we state that if you pitch at 100g/hL, you will achieve 6 mc/mL. That pitch rate is above the recommended rate for ale’s but the reason is as I stated before, our production procedures and the health of our yeast in the package. We do not have a list of the viable cells per sachet, but we have done time trials and have found that annually you will lose about 5% of the viability if the sachet is stored in a refrigerator and 10% if the sachet is stored at ambient temperature!!! Our yeast now has a three year best before date.
Can brewers reuse yeast? There is lots of talk about washing or rinsing yeast and using it again and again.
Can brewers reuse yeast? Good question. Simple answer is yes. I always remind people that dry yeast is yeast, we have just processed it so that it is shelf stable and the brewer doesn’t have to worry about doing a starter a day or two ahead of when they want to use it. The difficult answer is “yes, but be careful”. Remember that yeast is living and that every time yeast reproduces (buds) and creates new cells, there is a possibility of genetic mutation. These mutations can happen 10-20 times in one fermentation and can lead to a colony of yeast that is genetically different than what you started with. The “be careful” part of my response is related to this fact. Additionally, every time you reuse yeast, you introduce the possibility of introducing an infection: bacterial or wild yeast. With all of that said, you can reuse yeast and our company recommends 4-6 generations at the most. (my personal suggestion is no more than 3 times and handle it as little as possible, Ill post again soon about pitching onto yeast cakes in progressive OG beers) When reusing yeast, you have to do it knowing that you may end up with different fermentation kinetics and the possibility of different flavors coming from the yeast. This could be a good thing or it could be a really bad thing. If you want consistent beers every time, it is best practice to start with a new package. Remember that when commercial breweries reuse yeast, they have a team dedicated to yeast handling and they have the ability to acid wash the yeast (homebrewers can too, but it is a lengthy, difficult process) to kill bacteria and yeast that aren’t capable of surviving the acidic environment.
If a brewer re uses yeast, how many times can they use it before it mutates?
It depends on the environmental conditions and the strain its self. Some strains mutate faster and others slower over the course of fermentation and growth phases. It is hard to say how many times, because some strains will mutate the first time and others won’t for multiple generations.
What is the importance of temperature controlled fermentation? Which is more important control or consistent temperatures?
Temperature controlled fermentation is similar to using a new yeast package every time. The control is for consistent results for duplicating the beer. It would be the same as asking, “what is the importance of using the same amount of malts in the recipe” or “the same amount of hops at the same times”. If you change the fermentation parameters, you will change the outcome. Sometimes, you won’t see a difference, but other times you will. Both control and consistent temperatures are the same. Neither is more important, they both play a role in fermentation. (get a fermentation chamber, or two)
Best advice for new and intermediate brewers? Sanitation, Fermentation, Oxygen, Dry yeast?
Best advice I can give is…
Remember that as a brewer, you aren’t making beer. You are attempting to make the “right environment” for the yeast to produce the beer you are wanting. You are only able to control the wort before the yeast goes in. Once the yeast is pitched, the yeast do the work. REMEMBER this! Everything you do in cleaning, sanitizing, brewing, fermentation controls and parameters… all of that is for the yeast. Brewers are essentially glorified cleaners and “pet” caretakers. Humans don’t make beer, ONLY YEAST CAN (with the exception of GMO organisms, but that is a very different conversation)!
Great stuff from Kevin Lane. And there is more to come sports fans, so check back as we continue this series on The Actual Truth about yeast!
Prost!
We're taking a break from the yeast series for a day and we are having our first real give away! Not a corny everybody wins give away. An actual contest. The amazing people at BSG have donated 10lbs of Weyermann Barke Pilsner TM malt to Counterbrew for a contest. And one of you lucky readers will get to try this amazing grain for free. No cost, nada, zero, zippo... no postage, no handling... just free. The runner up will win 1# of some other German Specialty malt, that we have here at Counterbrew! An undermodified pilsner that can be used like a carapils. Also cool stuff. 
They want you to try this amazing Pilsner, and after using it a couple of times, I want you to try it too. This is simply put the best Pilsner malt I have ever used, and I brew a lot of german lagers. It extracts better than any I have tried, and the flavor is ridiculous.
