Do you clean and sanitize everything that touches your beer? Do you make sure to buy the best hops? Do you spend countless hours poring over blogs about whether you should ferment in plastic or glass? Many homebrewers take all of these great steps, but at the end of the brew day, they fail to get the wort to the optimum temperature for their yeast, fail to pitch the proper amount of yeast, and fail to control the temperature of their beer as it ferments. Out of all of the steps the homebrewer takes, cooling the wort to the proper temperature, pitching the proper amount of yeast, and then controlling the temperature of the fermentation are absolutely, without a doubt, the most important steps in making good beer. If you want to brew better beer, you need to think about your yeast. What does your yeast need? What will make it comfortable and healthy? You need to treat the yeast like a fancy house guest. Give it all you’ve got. Improving your homebrew may not require a lot of expensive ingredients or shiny steel conical fermenters either. In many cases, it won’t even matter if you ferment in plastic or glass, although I would vote glass, if you are asking. Plastic adds a distinct flavor that I don’t care for, plus you have to be careful with bacteria... but that’s for another article. Right now, we are focused on healthy yeast at a comfortable temperature.
Yeasts are temperamental, single-celled organisms. You throw them into your beer, and if you don’t have the right nutrients, temperature, and environment, they are going to throw a fit and this will involve the creation of off-flavors. It doesn’t matter if you spent $22 on a pound of Citra hops, equally too much on some golden promise malt, or even sprung for a CO2 tank and some kegs to help get that beer into a glass as soon as possible, or more importantly, to get that beer into your mouth as soon as possible. While all of these steps are good, obviously, they are somewhat pointless if you aren’t going to take care of your yeast. This is a basic step. Skipping this step is tantamount to buying the best toothpaste in the world and then brushing your teeth with a stick. It doesn’t make any sense. If you pitch yeast into hot, 85-90°F wort, some of the yeast may die and you may end up with a beer that exhibits some awful off-flavors. And if you don’t pitch enough yeast? Off-flavors. If you fail to control the temperature during fermentation? More off-flavors. Also, you will be sad, so very sad. Don’t you want to taste the pineapple and tropical flavors of your Citra hops? Well, if you make a beer with strong off-flavors, those brilliant waves of fruit flavor you were expecting from the Citra will be buried and you won’t be able to enjoy them, nor will you enjoy the distinctly sweet flavor of the golden promise malt that your LHBS charged you $2 a pound for. Instead, you will likely taste dead yeast, the acrid burn of fusel alcohols, green apple or pumpkin, and other potential off-flavors.
Homebrewers refer to dead or dying yeast as “yeast autolysis,” which is a fancy term for yeast self-destruction. The yeast cells die, the cell walls rupture (self-destruct), and off-flavors come out of the cells. A scientist from Iowa State University named Murli Dharmadhikari described this process as “self-degradation of the cellular constituents of a cell by its own enzymes following the death of the cell.” You can google her name and read more about her take on the subject if you wish. She published an interesting article that discusses the importance of yeast autolysis for the creation of sparkling wine, but I don’t know much about that. I’ve worked in two wineries but we didn’t do any sparkling wine. For the purposes of beer making, you simply want to avoid killing yeast. Killing yeast is bad and will result in a beer that is bad. Yeast autolysis can create the festive flavors of burnt rubber and cardboard, among other noxious and offensive aromas that will assault your nostrils. To avoid these undoubtedly terrible things, it is important to pitch yeast at the right temperature and to keep the fermentation in a comfortable range. When you pitch yeast into wort that is close to the target fermentation temperature, you will end up with better beer. The yeast likes to stay at a comfortable temperature and drastic changes make them unhappy. Oxygen is also helpful, or a very, very tiny amount of olive oil, although you should research the olive oil method prior to attempting it. For oxygen you can basically just sanitize and stick in the air hose. If you get a nice oxygen stone you might have better results though.
When a beer ferments at too high of a temperature, say an ale yeast in the 75-80°F range (and higher), the yeast will create more fusel alcohols. Renowned homebrewer John Palmer, the author of How to Brew, has likened fusel alcohols to cheap tequila. Essentially, you are going to taste the burn of alcohol, and not in a fun, chest-warming type of way like you’d get from a nice Schnapp’s in your coffee at a football game. This burn will be more like Jose Cuervo, or box wine, or cheap grain alcohol. You’ll pucker, wish the beer had a better mouthfeel and flavor, and also wonder why you are tasting alcohol instead of those quality ingredients that you spent so much money on.
This is Acetaldehyde. Beer will create a higher quantity of acetaldehyde if the yeast is not pitched into wort that has been cooled to the proper temperature and if that temperature is not maintained throughout fermentation. Acetaldehyde, as you likely guessed from the title, often tastes like green apple and is likened to other vegetal flavors. One problem with discussing off flavors is that they do not taste like the same thing to everyone because people, like yeast strains, are all different. I’ve had the joy of tasting through off-flavor kits with professional brewers and BJCP judges. These kits come with audio CDs to help you walk through the maze of flavors that beer can contain and part of the process involves pausing the tape to write down what you taste. Even professional brewers will realize that they did not understand an off-flavor until they do an off-flavor kit, which I would highly recommend. After you write what you taste, the tape will continue and describe the off flavor and the common terms used to describe it, like green apple for acetaldehyde. To some people, acetaldehyde does not taste like green apple or fresh cut pumpkin, despite the fact that John Palmer has told us that it does and published the same in a book. This description of the flavor is generalized so that it applies to most people, but you will not know if you are most people until you do an off-flavor kit or find some other way to isolate the flavor and to discover what you taste. Additionally, if you are tasting acetaldehyde, your beer might be young. Often, though, you may have failed to control the temperature of the wort when you pitched your yeast, causing more acetaldehyde to be produced by the yeast than would have been produced at a lower temperature. White Labs did a great study to illuminate the higher rate of acetaldehyde production in beers brewed at higher temperatures, which is discussed at length in Yeast: The Practical Guide to Beer Fermentation, by Chris White and Jamil Zainasheff. In this study, White Labs fermented a batch of beer with California Ale Yeast WLP001 at 66°F and another batch at 75°F. They used gas chromatography to evaluate the results of these two batches and juxtaposed the results in a table, which you can see in White and Zainasheff’s book. The biggest chemical difference between these batches of beer was by far and away the amount of acetaldehyde in each sample. For most people, acetaldehyde will not be perceived until it reaches 10 ppm (points per million). In the beer fermented at 65°F, the acetaldehyde was only 7.98 ppm, right below the flavor threshold of 10 ppm. That’s good. Most people will not taste that. The beer fermented at 75°F, on the other hand, had a whopping 152.19 ppm of acetaldehyde! That is approximately 10.5 times the flavor threshold and should be perceived as a strong punch of green apples and fresh pumpkins, like a club over the head.
For an ale yeast, the ideal temperature for pitching and for fermentation is absolutely below 80°F degrees Fahrenheit, and for most ale yeast strains, the ideal temperature is closer to 68°F. This can certainly vary, but as a rule of thumb* 68°F is certainly a good temperature to be at. At the end of a brew day, I prefer to cool my beer until it is a degree or two lower than my target fermentation temperature. For instance, if you want to keep your fermentation at 68°F, try to cool the beer to 66-67°F. If you are cooling with tap water, the last few degrees might take a while, or you may simply have water that is too warm to achieve this. If you can get it at least to the low seventies you should be ok, though, and ready to make some great beer. *Many people know that “Rule of Thumb” is a somewhat sexist term, as it refers to the width of stick that you can acceptably beat your significant other with. I use this term with as much humor as possible and certainly don’t mean to offend anyone. Many of you are probably thinking, “I’ve pitched beer at 85°F before and fermented beer. I drank it. Why do I need to go lower?” Well, you want to go lower because you want to brew better beer. Fermentation creates heat. Why yes, you can pitch your yeast when the wort is at 85°F, but if fermentation creates heat, where will the beer go from there? Up. It might hit 5 to 7°F over your starting temperature before it cools back down. Heat spikes during the first 72 hours of brewing and creates the most distinct flavors in beer. Distinct flavors can be good, but some of those flavors are not good and will overwhelm the ingredients that you spent hours putting together. For a lager strain, you need to pitch your yeast into wort that is around 45-55°F. It is especially important to cool the wort for a lager to pitching or below pitching temperature before you toss your yeast in. While you can sometimes brew a great beer without doing this, you will often be stuck with a beer that has a strong diacetyl off-flavor, which is an acceptable flavor at low levels, but not really ideal.
If you ferment at too low of a temperature, you risk a stuck fermentation. There is a happy place where your yeast wants to live and you need to find it. Yeast depends on a consistent temperature and they create heat through the process of fermentation. If you ferment at 60°F, and the yeast creates 5 to 7°F of heat, then you are probably at a comfortable temperature. One problem with fermenting at temperatures as low as 60°F is that the fermentation will slow, especially after the first 72 hours. Then, the 5 to 7°F you were depending on will disappear and the temperature will go lower. To yeast, a 5 to 7°F drop is significant. They are single cell organisms and will immediately feel the change through their tiny cell walls. That being said, you can go much lower with an ale yeast strain, and obviously you need to go much lower with a lager yeast strain. I have gone as low as 59°F with an American ale yeast in a cream ale, although I monitored the fermentation closely and raised the temperature slowly over the first 72 hours until I arrived at 68°F, plus or minus 2 °F. Monitoring the temperature closely and raising it a few degrees as the fermentation slows can go a very long way to keeping the yeast healthy and making the beer clean. A clean beer, at least in my view, is one with less yeast character and one that does not exhibit off-flavors. Temperature fluctuations will certainly change the flavors of a beer for better or worse and reading about each yeast strain can be an incredibly useful experience to see what types of flavors you can get. It is probably safer to keep the fermentation a bit higher than 60°F, even if you enjoy needlessly monitoring and adjusting the temperature like I do. I have had better luck setting my digital temperature controller to 66°F -68°F. This tends to produce a beer that is drier with a yeast character that I enjoy. When all else fails, go to the manufacturer’s website and check out the yeast strain that you are using. You should find a range of alcohol that the yeast can safely ferment (i.e. up to 11% ABV) and you should also find the best temperature ranges to ferment the beer. Within that temperature range, you will simply have to experiment until you find the flavors that you like. This is a constantly discussed subject on Homebrewtalk and one interesting thread that beats this discussion into the ground revolves around a yeast strain called Conan, which is used in the Alchemist’s famed DIPA, Heady Topper. There are 61 pages discussing fermentation with this yeast strain alone. I read through every page that I could before harvesting Conan yeast from Heady Topper cans and before making a beer with the yeast that I called Heady the Elder and I can tell you, the research and experience of other members really helped me determine the fermentation temperature for that yeast. This type of research is a good alternative to doing 17 of your own experiments or at the very least, it can get you started on the right path so you can make a beer that you want to drink.
Proper pitching rates are usually in some range of billions of cells, for ale or lager yeasts. After pitching, the yeast will produce billions more cells, but they are reproducing inside of your beer. Just like when other organisms reproduce, there will be byproducts. You don’t want too much of any of these byproducts inside your beer or it may turn out a bit yucky. Good luck with your next batch and I hope some of my random thoughts help make your beer taste even sweeter (or hoppier, if that’s what you’re going for). Cheers!
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