It has been a busy time in Wizardsburg, but I come back to you now at the turning of the tide. Glad to have you around for our semi-regular chats here. I enjoy them. Now, on to business…
Time for some uncomfortable truth: brewers don’t make beer. We couldn’t in a million years. We can, however, make some sugary barley water, add a few flowers, and let yeast make beer. It’s those guys that really work the magic. Vast armies of microscopic fungi are the true heroes of every pint, and the best we can do is care for them and make their job as easy as possible. To that end, let’s spend a little time thinking about the most common genus of brewers’ yeast: saccharomyces. “Wild” organisms like brett and lacto are very sexy in the current beer climate, but there is no disputing the dominance of saccharomyces as the true lord and master of beer fermentation. As popular as wild beers are, they are absolutely dwarfed by the amount of beer that relies solely on sacc to transform sugar water into delicious beer.
First, some exceedingly brief biology. Though there is a substantial array of species inside the monocellular fungal genus saccharomyces, many with some useful industrial application, the two species that interest us most in brewing are saccharomyces cerevisiae (ale yeast) and saccharomyces pastorianus or, as it is sometimes called, saccharomyces carlsbergensis (lager yeast). Anyone who has spent a moment browsing a brewing yeast catalogue can tell you that there are also a massive number of strains within each of these species, but for the purposes of this overview, we are going to treat each species as roughly homogeneous. Not strictly true, but a useful fiction for the depth of this article. The word saccharomyces literally translates to sugar fungus. They eat (many) sugars in the wort and produce large amounts of CO2 and alcohol along with a cornucopia of lesser by-products that can have a massive effect on the final beer. As with humans, there are a handful of environmental factors necessary to sustain yeast life. Once those basics have been met, it is attention to fine tuning that really determines the quality of product. Again, as with humans, yeast perform best when they are given proper nutrition, an appropriate environment, the right work to do, and the tools to do that work.
The factors that we will deal, albeit briefly, with here are pitch rates, temperature, and nutrition. I’ll be gently stretching the definition of nutrition, but we’ll get to that in a minute.
Pitch rates are extremely important. To continue abusing the yeast/human analogy, if you take one guy to a construction site and tell him to build a large building, that building is unlikely to get done. If you take a small crew to a big job, they might be able to get it done but probably not as fast or as well as you want. If you take too many workers, the job will probably get done, but you will have wasted a lot of resources hiring them all. Ok, let’s let the analogy die. Pitch the right number of yeast cells for the beer you are trying to make. The illustrious Dr. George Fix has determined that the appropriate pitching rate for ales is 0.75 million cells per mL per degree Plato. He recommends double for lagers. Because few of us are as adept as Dr. Fix and because I prefer a slight overpitch to a slight underpitch, I tend toward the nice round numbers of 1 and 2 (million cells per mL per degree Plato). Preferably, you will have access to the equipment necessary to test your yeast source for cell density and viability. This includes, at minimum, an appropriate counting chamber, a good microscope, and dilution equipment. Once you have done that, you can use the above calculation to figure out the volume of yeast you need. If you don’t have said equipment, you can contact any yeast manufacturer for details on their commercially available yeasts or use the extremely rough calculation of 1 billion cells per mL of fresh settled slurry. If you have the ability to measure these things, absolutely do that. Practically, I realize many brewers do not, so the following simple formula can be used to approximate if you are pitching fresh, viable, settled yeast slurry:
(Volume of batch * OG in Plato)/1000 = Volume of yeast needed for ale fermentation
Don’t tell anyone I told you, and remember to keep you volume units consistent.
Next let’s talk temperature a little bit. This is another extremely controllable and extremely important factor. Obviously the more complex your setup, the more control you may have over temperature, but the fact remains that the more you stay inside appropriate ranges and the more control you have over appropriate temperature changes, the better your results will be. Know the preferred fermentation range of the strain you are using, and stick to it. Ales are generally warmer than lagers, but individual strains can have vastly different ideal ranges. If you try to save a little time by pitching outside the range when you could get the temperature spot on, you are making a big gamble. Get to pitching temp and keep it as steady as possible. Cellular reproduction outside the recommended range can reduce viability, stall out fermentation, and produce unwanted flavors. If you have a planned temperature change such as a diacetyl rest, try to limit your swing to one degree Fahrenheit every two hours. Use the same rate if you accidently pitched too warm and have to cool down. Rapid temperature changes can also stress the yeast and result in reduced viability and off flavors. Feel free to move more quickly though, if you are crashing your beer post-fermentation. Dormant yeast at the end of their reproduction cycle can tolerate more rapid chilling.
Now nutrition. As I said, I am going to stretch the definition slightly and include sugars, other minerals, and oxygen in this section. Not all consumed through the same mechanisms but all necessary chemicals for biological success. Yeast perform best with an adequate amount of fermentable sugars. As a general rule, shorter chain sugars will be more fermentable, and longer chain sugars are less fermentable. A wort full of lactose is not likely to ferment very well while a pure maltose wort has an excellent chance of high attentuation. Though unfermentable sugars are necessary to enhance body, mouthfeel, and flavor, you must also take care to provide your yeast with sufficient fermentables to keep the final product from being “flabby”. This is normally not a problem with an all-barley wort mashed at a reasonable temperature, but if you mash in with 50% oats at 175F and boil for 3 hours with a lactose addition, you’re going to have a bad time.
Most of the data on minerals have been covered in my article on salt ions, but a brief reiteration is in order. Yeast can only function if they have 100% of the minerals necessary to perform their next biological task. Though the amounts they need are quite small, their need for them is absolute. Make sure you have sufficient calcium, magnesium, potassium, and zinc in your wort. Most barley worts will have plenty of these things, but a little hard water, a small ion addition, and some commercially available yeast nutrient can all help provide sufficient minerals for yeast activity.
Oxygen is the last necessity we will be mentioning today. Upon reproduction, yeast must acquire or synthesize sterols to strengthen the lipid membrane of their progeny. While there may be some sterols available in non-aerated wort, proper levels of dissolved oxygen allow the yeast to create their own sterols. Yay! Regular atmospheric aeration can provide plenty of oxygen for normal wort, but higher gravity worts or worts with plenty of unfermentables can benefit immensely from pure oxygenation. A simple oxygen stone can provide the dissolved oxygen levels necessary to construct all the needed lipid membranes. While it is possible to over oxygenate and set your beer up for an oxidized fate, you do have to go heavily overboard for that to be a legitimate risk as yeast will consume fairly vast amounts of oxygen and often scrub the rest out of solution through the mechanics of CO2 generation.
Well, that’s all I have on the topic of caring for your sacc. I hope you enjoyed. Until next time, faithful readers, thanks for reading, and happy drinks!
P.S. Remember to let me know if you have some specific topic you would like me to babble about next time. You can tell me in person, by e-mail, or in the comments right down below.