“Look, we said it at the start of this whole thing and we’ve said it several times since—your yeast health matters. It matters more than anything else you do in the brewery.”
You’ve collected your equipment, picked out a recipe, gotten your ingredients, and made a batch of wort. Congratulations! Now, there’s just one more step to making beer: fermenting that wort into the magic elixir you’ve been thirsting for. How hard can this be? You just toss in the yeast and wait a couple weeks, right?
Well, kind of … Maybe it’s because there’s minimal effort involved, but we’ve run across too many brewers who don’t take fermentation as seriously as it should be taken. It’s not hard to ferment your beer properly. If you want an incentive to do it right, remember this: if you don’t properly control your fermentation, all the time, effort, and money you’ve put in up till now could be wasted, and that’s a serious bummer.
Yeast was the last beer ingredient to be enumerated. We hesitate to say discovered, because really those little fungi have been around longer than we have, so it seems imperious to say we discovered them. If you look at the Reinheitsgebot, the purity law for beer drawn up in Bavaria in 1516, you see that the only ingredients listed are malt, hops, and water. Yeast wasn’t isolated and identified as the cause of fermentation until Pasteur described it several hundred years later.
There are endless stories of families making beer and stirring it with a “magic stick” in order to get it to ferment. Since even Denny isn’t old enough to have been around back then, we have to assume that the stick had previous yeast embedded in it and stirring with it transferred some of the yeast to the wort. Hey, it makes for a good story!
Once the yeast meets the sugar-rich wort, it begins fermenting immediately while also growing more yeast cells. It was once thought that there were distinct stages that occurred before the yeast’s metabolism switched to fermentation, but it’s now known that everything kind of happens at once.
Besides more yeast cells, two other very important things are created: alcohol and carbon dioxide (CO2), which are by-products of yeast metabolism. That’s what we’re really interested in! As the beer ferments, the food for the yeast (the fermentable sugars in wort) runs out and the alcohol content increases to a point where the environment becomes hostile for the yeast. At that point, the yeast goes dormant. But it’s not dead. You can harvest some of the yeast from the fermentor and reuse it in future beers.
Besides creating alcohol and CO2, the yeast also creates flavors in the beer. What kind of flavors and how much of them are in your beer is primarily determined by two things: the particular strain of yeast you use and the temperature at which you ferment.
In brewing we’re primarily interested in two types of yeast: ale yeast, Saccharomyces cerevisiae; and lager yeast, Saccharomyces pastorianus (a.k.a. S. carlsbergensis after the Carlsberg Brewery where it was isolated). These two main types come in hundreds of strains (and some even weirder variants that we’ll cover later).
Each strain of yeast will differ slightly in terms of attenuation, which is how much of the sugar in the wort it will ferment, and flocculation, which is how well a strain drops out of suspension in order to clarify your beer.
Additionally, each strain produces different by-products that provide the actual organoleptic sensations in beer that we know and love. There are a few simple rules. In general, fermenting at lower temperatures produces cleaner flavors with less flavor contribution from the yeast; fermenting at higher temperatures results in the yeast contributing more fruity esters to the beer. With strains that give off spice characters (a.k.a. phenols) like cinnamon, nutmeg, and cloves, cooler temperatures emphasize them, but not because there’s a magical switch inside the yeast. It’s simply because the higher temperatures will emphasize the fruitier characteristics of the yeast, which makes it harder for your palate to pick out the phenols.
But wait, there’s more!
There are other Saccharomyces species out in the world, and it turns out more than one critter figured out that sugar is useful! S. bayanus is most commonly associated with wine and cider and does fun things when mixed with beer yeasts, including killing them dead. There’s S. eubayanus, a strain first isolated in Argentina but also found in other places, that turns out to be one of the parents (along with S. cerevisiae) of our lager yeast, S. pastorianus. Scientists are still puzzling out how all that came about. There are many other species, but they aren’t generally used in the world of brewing.
A genus of wild yeasts called Brettanomyces (which translates to “British fungus”!) can be used in conjunction with other yeasts to impart characters to the beer ranging from fruit to a funky barnyard character. Brettanomyces was once thought to be a bacteria, but subsequent DNA analysis has shown it to be another variant of yeast.
But that doesn’t mean that bacteria can’t be useful in brewing. As weird a thought as that might be, things like enteric or lactic bacteria can add layers of complex flavor to some styles. Many Belgian styles owe their existence to these bacteria. That’s enough of that for now. Join us in chapter 11 for even more bacterial weirdly goodness.
You may be wondering about some other terms thrown around about yeast like “top fermenting” and “bottom fermenting.” Those terms came from the really old tests for separating ales and lagers. Ale yeasts were said to be top fermenting—the yeast rose to the top on a big rocky kräusen in the fermentor, perfect for capturing and reusing the yeast. Lager yeasts typically don’t throw a big kräusen so the yeast settles to the bottom without ever really rising up, hence lager yeasts were said to be bottom fermenting. Later testing determined that rule of thumb was insufficient. Lager and ale strains were then identified based on their ability to ferment some of the longer chain sugars, such as raffinose. And then, because of the way of the world, even that turned out to be insufficient. Nowadays, for proper classification, scientists are increasingly turning to genetic testing to fixedly determine which way is north.
In chapter 6, we divided yeast by flavor into the categories of clean, estery and fruity, phenolic, and sulfury. Let’s see how those characteristics relate to the particular species of yeast. There are two yeast genera that are intentionally used for brewing beer: Saccharomyces and Brettanomyces. There are several species within these genera that are used, and then various strains of those species besides.
In terms of flavor, ale yeast exhibits the largest variation of any of the yeast types used for brewing. Ale yeast can be squeaky clean, imparting no flavor of its own, to dramatically fruity, with distinct flavors and aromas like apple or berries, to phenolic, with notes of smoke or clove.
With such a wide range of flavors available, choice of yeast becomes as important as the choice of any other ingredient in your beer. Sometimes you want a very clean yeast that will impart no flavors of its own in order to let your malt and hops shine through. Other times the entire character of the beer can be defined by the yeast flavors. German hefeweizen, for example, would simply be a relatively flavorless wheat beer without hefeweizen yeast imparting the distinctive banana and clove flavors the beer is noted for. And if you ever want to be trapped in a discussion for hours (or days), ask Drew about the various saison yeast strains that exist. Bring provisions, you’ll need them.
Most ale yeasts will perform best in the temperature range 60–70°F (15.5–21°C). Some will work at lower temperatures and produce even cleaner profiles, which is great for “pseudo lagers,” ales with the low ester character of a lager.
Lager yeasts have a lot less obvious variance than ale yeasts. They’re a little more subtle, which for homebrewers may be beyond our typical scale of exploration. Lager yeasts are almost always very clean yeasts, although some tend to throw more sulfur or diacetyl characters than others. They are meant to be fermented at lower temperatures (48–55°F/9–13°C) than most ale yeasts. Some lager yeasts perform well at higher temperatures, but the general belief (and tradition) is that high fermentation temperatures should be avoided with lager yeast. Of course, as with all things dogmatic, these views have been challenged. There are even strains that produce amazing results at increased pressures, but that requires a bit of technology. (Check out our Experimental Homebrewing podcast for instructions on building a “spunding valve.”1)
The reason lager yeast have come to rule the world (if you look outside the world of specialty craft and microbrewing, it really has) comes down to its ability to more completely ferment the complex sugars found in barley wort. Earlier, we mentioned that the old technique of classifying strains used raffinose. If grown in media containing raffinose, a typical ale yeast cannot completely break it down, leaving behind a residual sugar, melibiose. Lager strains, however, do have the ability to completely ferment raffinose, breaking it down to melibiose and then degrading the melibiose to glucose and galactose. Although raffinose is not usually present in beer wort, a small amount of melibiose is, which lager yeast can consume. The end result in the beer is something a bit drier and crisper, part of that mystical refreshing character that lagers have.
Lager strains do produce a few funnier things in excess of their ale counterparts (or at least the aromas are more prominent in lagers), namely, sulfurous characters. Some lager strains straight up throw hydrogen sulfide, a.k.a. the smell of rotten eggs. Other strains are prone to producing dimethyl sulfide (DMS) in the right conditions, which gives a cooked corn or cabbage aroma. Both of these results are avoidable via strain selection and proper wort handling. (Follow the basic guidelines of brewing and you’re fine!)
Why has homebrewing and craft brewing been so largely ale-focused when there are the mighty lagers? The first reason is that typical lager fermentations require temperatures in the 50–55°F (10–13°C) range, which is not as easily achieved as the ale range of 64–70°F (18–21°C). The second reason is the long, cold storage necessary for maturation—the “lagering” of lager beer. Lagering requires more temperature control, more time, and more space to keep fermentations moving along.
Brettanomyces (or “Brett”) produces flavors that at first may make you think, “Why the heck would I want my beer to taste like that?” The flavors Brett produces are often described as barnyard, horse blanket, smoky, Band-Aid, foot odor, and putrid cheese … yum! Why would you want those in your beer? Because in the right amount mixed with the other flavors in your beer, they can create a depth and complexity that’s not only intriguing but also delicious. And to be fair, there are some strains of Brett that create pleasant fruity flavors, like orange and pineapple. As a brewer, you will generally be working with one (or more) of three species of Brett: Brettanomyces bruxellensis, B. claussenii, and B. lambicus.
Brettanomyces bruxellensis (available as White Labs WLP650 and Wyeast 5112) is probably the most common species of Brett used in beer. Named for the city of Brussels, this is the strain that Orval uses to dose bottles of its beer. Anyone who’s ever had an Orval knows that you chose your bottle by the age. Younger bottles will have a pleasantly fruity quality to them. As the bottles age, the Brett gets more aggressive and funky, getting into the classic sweaty, horse blanket flavors.
Brettanomyces claussenii (White Labs WLP 645) is at the opposite end of the Brett spectrum. It has a fruity pineapple-like flavor and can often be tasted in classic barrel-aged British ales.
Brettanomyces lambicus (White Labs WLP653 and Wyeast 5526) is associated with Flanders ales. It is intensely funky and sour. Just the thing for those styles!
Brett is usually used after fermentation with an ale yeast, although there are beers made with 100% Brett. Once fermentation is complete, or nearly so, you add the Brett along with something else (usually fruit) to provide sugar for the Brett to work on. Brett is occasionally used on its own, but not often.
So, now you have choices to make: clean, fruity, or funky; high temperature or low temperature? But you’re not done yet … you have one more choice to make.
When we started homebrewing, liquid yeast was just starting to appear on the market. Before that, all yeast was only available as dry yeast, similar to bread yeast. In fact, bread yeast and beer yeast are the same genus. The difference is that beer yeast strains have been selected to produce alcohol while bread yeast strains have been selected to produce CO2 to make bread rise.
In years past, dry yeast was kind of looked down on as being inferior to liquid yeast. Due to imperfect manufacturing processes, brewers would often get dry yeast packages that were contaminated.
The other disadvantage with dry yeast, historically, has been strain selection. Until the past few years, you had basic choices like “here’s an ale strain and another ale strain that’s like a lager.” Slowly, the yeast manufacturers have been introducing new strains for our variety loving brewing ways. Today there are genuine lager strains available dry, like Fermentis’ Saflager W-34/70 and Lallemand’s Diamond Lager yeast.
Dry yeast does have its advantages though. It tends to cost less per package and it stores for longer periods of time. Packs have years-long shelf lives as long as you keep them refrigerated.
Liquid yeast gives you a lot more variety when it comes to selecting just the right yeast for your beer. This is especially helpful when you want to make a beer, such as a hefeweizen or a Belgian style, that gets a large part of its flavor from the yeast. The trade-off is that using liquid yeast takes a little more effort than using dry yeast. In most cases you’ll want to increase the cell count of the liquid yeast you’re pitching into your beer. Liquid yeast manufacturers claim that there are sufficient cells in their packages to ferment 5 gallons of a 1.060 OG beer. And we don’t doubt them … It’s just that the viability of the yeast starts decreasing the moment it’s packaged, so when you get the yeast you may not have much of an idea how much happy yeast is left in the package.
The biggest advantage of dry yeast is that it’s easy to use. Simply open a pack and pour it into your wort. Many people prefer to rehydrate the yeast in lukewarm water for a few minutes before adding it to the wort. Rehydrating means that you’ll be pitching a larger amount of viable cells than if you just dumped the yeast in. But is that really necessary?
A package of dry yeast contains many more yeast cells than a pack of liquid yeast, but it still may not contain enough cells for the beer you want to brew. By rehydrating the yeast in water before putting it in your beer, the nutrients dissolve and become available to the yeast in order to grow more cells. If you simply pour the pack into your freshly brewed wort, the sugar in the wort causes an increase in osmotic pressure on the cells compared to using water. That increased pressure will kill a number of your yeast cells, but there will likely still be plenty to get your beer off to a good fermentation. At least, maybe, depending on the beer you’re making.
There seems to be disagreement about how many cells are in a pack of dry yeast. Some people claim that there are as many as 18 billion cells per gram of dry yeast. Fermentis, a major manufacturer of dry yeast, says that there are 6 billion cells per gram in their packs. Lallemand, another major manufacturer, puts theirs closer to 5 billion cells per gram. But both companies say that an 11 g pack of their dry yeast is more than enough for 5 gal. (19 L) of 1.060 (14.7°P) wort. Both companies also used to recommend on their websites that you rehydrate the yeast before pitching it into your beer, but now there are conflicting opinions.
You want to make sure when rehydrating not to use water that’s too warm. Yeast can be killed if the water is over about 114°F (45°C), so you need to be careful to keep your rehydration water around 95–100°F (35–38°C).
The biggest downside of dry yeast is the lack of variety. There are some strains of yeast that just don’t take to drying as well as others. The number of different dry yeasts is always expanding though, so hopefully one day there will be nearly as much variety as there is for liquid yeast.
With liquid yeast you generally need to make a starter to increase the number of healthy yeast cells. A starter is basically a very small batch of beer. There’s no need to use hops in it because you’re not going to drink it! You’re growing yeast, not making beer. Yeast grows best in a lower gravity environment, so you want to keep the specific gravity of your starter around 1.035 (8.8°P). Also, yeast grows better at warmer temperatures than beer is usually fermented at.
So, how many yeast cells do you need and how do you figure out how to get them? For an ale, you need 6–18 million cells per milliliter, depending on the original gravity (OG) of your beer. For a lager, the top end increases to at least 24 million cells per milliliter, again depending on OG. The higher the gravity, the more yeast you need.
Wyeast and White Labs, the two major producers of liquid yeast, both say that their packages contain about 100 billion yeast cells. Their websites claim one package is sufficient for 5 gallons of beer with an OG of 1.060.
One way to figure out how much yeast to pitch is to use a yeast calculator. Calculators are often available as part of brewing software, as well as on several websites. A calculator will generally ask you for the date the yeast was manufactured so it can make an educated guess at how many viable cells might be in the pack. It will ask you for the amount of beer you’re intending to make and what the original gravity will be. It will probably ask you if you’re making a simple starter (simply putting the yeast in and letting it sit), or if you’re using a stir plate or aeration with your starter. All of those things factor into how big a starter you’ll make and how long it will take.
Denny did starters by the numbers for many years, the whole sciency, stir-plate-and-flask kind of thing. Yeah, it was effective, but it was also a pain. You had to make the starter several days to a week in advance of brewing, then refrigerate it for a day or two in order to help the yeast settle on the bottom. On the day of brewing you decant the spent wort, leaving just the yeast slurry behind and that slurry gets pitched into your new wort. And then, one day there was a revelation.
A commenter appeared on the AHA discussion forum, “S. Cerevisiae.”2 It was obvious that this commenter knew more about yeast than most people think there is to know. He pointed out that the calculators were doing nothing more than making a wild guess at the starting yeast viability and the amount of growth that would occur. He also mentioned there was a potential problem with using a stir plate that could damage the cells as it stirred them, pointing out that the yeast manufacturers didn’t use stir plates because of that.
The commenter advocated a yeast starter method called “Shaken, Not Stirred.” His ideas were resisted at first because they didn’t sound appropriately sciency. But when you look at it, you see that what this commenter was talking about was the same method that Denny used in the late 1990s when he first started making yeast starters. Science might advance with every passing year, but sometimes the old ways are still valid.
The idea is to make what’s called a “vitality starter.” Unlike the starters based on calculated cell count (called a viability starter), the idea with a vitality starter is to pitch actively working yeast already fermenting strongly and ready to do its business in your wort. You use the starter to somewhat increase the cell count, but less so than in a viability starter. The real beauty of a vitality starter is that it’s working before it even goes into your beer!
A vitality starter for 5 gallons of average strength (1.050–1.075 OG) wort starts with a quart of 1.035 wort in a gallon container (Denny uses a glass apple juice jug, Drew uses a large, oversized chemical reagent jug). The day before you brew, bring a quart (~1 L) of water to a boil. Remove it from the heat and stir in 3 oz. (85 g) of light dry malt extract and a pinch (⅛ tsp or less) of yeast nutrient. You can get by without the nutrient, but it’s cheap insurance so we prefer to use it. Return to the heat and boil for 5 minutes or so. Cool the wort under 80°F (27°C). Denny cools his by putting it in a sink of ice water and monitoring the temperature.
Once the wort has cooled down, pour it into a sanitized starter container. After putting your cooled wort into the container, shake it until the container is filled with foam. The foam contains oxygen that the yeast will use to synthesize sterols, which will keep cell walls flexible and encourage budding (cell division and growth). The more foam, the more oxygen in your wort and the more subsequent cell growth. Now pour in your liquid yeast. Set the container in a place where it can stay between 60–80°F (16–27°C).
The next day, your starter will be ready to go. When you pitch it, the entire actively fermenting starter goes in. No refrigerating and decanting like you would do with a starter made on a stir plate. In fact, no stir plate! All in all, it’s a much more straightforward, dare we say simple, process.
But the best part is that it works at least as well as the calculator and stir plate method. Yeah, it’s cool to feel like a real scientist when you make a starter in a flask on a stir plate. But it’s also a waste of time and effort. And those are two things that we don’t want to waste.
If you’re wondering about the world of bigger fermentations—say, above 1.080 OG or so—we actually recommend the simplest way to deal with the yeast is fermenting a lower gravity batch of beer and then using the yeast cake from that to drive the ferment of the “monster” batch. Drew does this all the time. His high gravity Falconsclaws lager, which starts at 1.140 OG and uses a lager yeast that traditionally requires more yeast cells to begin with, is fermented with half a cake of Zurich lager yeast from a 5 gal. batch of a modest gravity schwarzbier or traditional bock.
You’ve got your yeast and it’s raring to go. Those little unicellular fungi are champing at the bit to gorge themselves on a buffet of sugary goodness, like a rabid pack of six-year-olds at Halloween. Our challenge as brewers is to keep the partygoers happy, the mess to a minimum, and the level of energy controlled and somewhat calmer than an explosion.
If yeast health is job number 1 for brewers, fermentation temperature control is number 2. (For the record, sanitation is really job number 1.5, but why ruin a perfectly cromulent list?)
If we were running a professional brewery, this is where we’d tell you to break out the glycol-jacketed fermentors and just punch in a temperature. (And hey, big surprise, some homebrewers have these types of gadgets—you crazy loons!) While you don’t need a gleaming super-cooled stainless steel fermenting vessel, you do need to control your temperature!
Temperature is what controls the growth rate of the yeast and that growth rate in turn controls what by-products the yeast produce and in what amounts. Keep in mind, in order to know how to control the temperature you have to know what the temperature is. The stick-on thermometers that go on the outside of your fermentor are remarkably accurate. We recommend that you put one on every fermentor you have.
Before we start talking about why fermentation temperature control is important and how you do it, we need to define a couple of terms you’ll often hear used to describe flavors and aromas created by yeast.
Esters are chemical compounds that usually manifest themselves as fruity. Apple, banana, pear, honey, and roses are examples of esters that may be found in beer. Sometimes esters are unwanted, but other times yeast strains are specifically selected for the esters they impart to beer. For example, German hefeweizen yeast produces a banana flavor and aroma due to an ester known as isoamyl acetate.
Phenols tend to show themselves as clove-like, medicinal, or smoky. Generally, phenols are considered undesirable in beer. An example is cholorophenols, created by using water than has chlorine or chloramine in it. If you’ve ever tasted a homebrew that reminded you of Band-Aids, you’ve had the unfortunate experience of tasting chlorophenols. But sometimes phenols are desirable. The smokiness of a rauchbier or the clove notes of a good hefeweizen are examples of desirable phenols.
The thing to be aware of for beer fermentation temperatures is that cooler temperatures lead to cleaner, less estery beers, while higher temperatures produce more fruity esters. So, fermentation temperature gets manipulated depending on what type of beer you make. A British ale, where those fruity notes are desirable, benefits from a bit higher fermentation temperature than an American ale, which in general should get less of its character from the yeast.
Short of getting yourself a glycol jacket or a big walk-in cold box (so jealous of the people with those), there are really only a few ways of getting your beer to stay at the right temperature. But first …
Primary rule for controlling fermentation: Short of supercharged cooling mechanisms, you will not be able to force a beer’s temperature down once fermentation starts kicking into high gear. In other words, don’t cool your wort in the kettle to 75°F, pitch a bunch of yeast, and then try and lower it to 50°F for lager fermentation. Fermentation is exothermic (heat generating)—once it kicks off, your fridge isn’t going to budge that wort mass down any.
OK, so we’ve got that out of the way. Chill your wort to fermentation temperature prior to pitching your yeast. If your kettle chilling can only get you down to 75°F (24°C), it would be best to offer a quick prayer to the beer gods, trust in your sanitation, and put the fermentor somewhere chilly until it’s cool enough.
There are three primary ways of controlling your fermentation: ambient air, a water bath, or a fridge/freezer. The first method, ambient air, is the “trust in your weather forecast/air conditioning” method. In other words, you stick your fermentor somewhere cool and leave it be. While achingly simple, the big disadvantage with relying on ambient air is that fermentation can raise the temperature of your wort in the neighborhood of 10–15°F (5–8°C), which means for an ale you want your fermentation space to be, say, 50–55°F (10–13°C). That’s a little cooler than most of us can manage.
The second method is using a water bath along with ice and/or a heater. Placing your fermentor in a water bath and using ice or a heater to stabilize the water bath temperature is the cheapest, easiest, and least accurate way of managing your temperatures. But, boy, is it attractive from a cost standpoint—really, as a fan of cheap and easy it’s hard to beat. For many years, Denny used the tub of water method. He put a large plastic garden bucket in a spare closet (dark, right?), filled the bucket with water, and then put his fermentor in the water. To cool things down, Denny used frozen ice packs that he dropped into the water in the bucket. To warm things up, he had an aquarium heater in the water in the bucket. Denny also used (and still does) Fermometer strips on his fermentors to monitor the temperature. His tests have found these strips to be very accurate, or good enough for beer at the very least!
The fridge/freezer method also requires a thermostat and probe set-up, but this method affords you more control over your fermentation temperatures. Air is a lousy cooling mechanism. It has no thermal capacity, which makes it really difficult for it to move the temperature of the wort. In other words, get your wort near/at the temperature you want it to ferment at before the yeast takes off. Don’t think you can pitch yeast into wort at 75°F, stick it in a fridge set to 65°F and expect it to cool the wort that low before the yeast is generating a ton of heat.
These days, Denny has a 15 cu. ft. chest freezer that he uses as a fermentation chamber. It is plugged into a temperature controller that has its probe taped to the side of his bucket fermentor. Also plugged into the controller is a reptile heater bulb. Denny sets the minimum and maximum temperatures he wants the freezer to get to using the controller. If it gets too warm, the freezer comes on until it hits the preset temperature. If it gets too cool, the heater bulb comes on. A reptile heater bulb is a great way to warm up a fermentation chamber that’s too cold. They’re easy to use, relatively inexpensive, and because they’re ultraviolet they give off no beer-spoiling light.
The kind of set-up above that Denny has is very effective and simple, but it’s not the cheapest way to go. Another trade-off of money for simplicity.
One of the great advantages of setting up a fermentation chamber in a refrigerator or chest freezer is being able to easily and accurately manipulate the temperature of your fermenting beer. Manipulating the fermentation temperature allows you to get your beer ready to drink faster than if you simply let it sit at one temperature for a couple of weeks. The idea is based on the fact that the majority of esters are produced in the first few days of fermentation. After that, you can safely raise the temperature in order to get the beer to ferment more quickly. And once it’s done fermenting, you can easily drop the temperature to near freezing to help clear the beer. Although the concept is the same for both ales and lagers, the specifics vary a bit.
For ales, start off in the 63–65°F (17–18°C) range. This might seem low based on yeast manufacturers’ recommendations, but it will be fine for just about any ale yeast out there. Leave it at that temperature for 4–5 days, which will get you through the bulk of the fermentation. On day 5 or 6, raise the temperature to 70–72°F (21–22°C) and leave it there until the fermentation is done. Depending on the beer, that can be anywhere from two to five more days. Use the tips below to determine when fermentation is done.
For lagers, start the beer in the range of 50–55°F (10–13°C). After about four days, check the gravity of the beer. You want it to be at about 50% toward your expected (or guesstimated) final gravity (FG). At that point, raise the temperature by 3 degrees Fahrenheit (~1–1.5°C) and leave it there until the beer is about 75% of the way to your expected FG. At that point, raise the temperature to 62°F (17°C) and hold that until the beer is 90% of the way toward your expected FG. At that point, raise the temperature to 66°F (19°C) until the beer reaches your expected FG. Using this method, 75% of your fermentation will be done at 58°F or less.
With either an ale or lager, once you hit FG, drop the temperature to 33°F (0.5°C). An ale should spend anywhere from 3–7 days at this temperature. A lager will take anywhere from a week to several months, depending on how long you can wait!
Probably the biggest question people have about fermentation is how to tell when it’s done. Denny likes to say, “The beer makes the schedule, not the calendar,” but that’s pretty lame (although he thinks it’s clever).
In truth, the only way to be certain fermentation is finished is to take a specific gravity reading. When you get the same result three days in a row, the beer is done and ready for the next step. But how do you know when to take a reading? So many questions, but there are answers …
You can almost never go wrong in anything related to brewing by just waiting a little longer. If you’re not sure the beer is done, wait a few more days. In most cases, for most beers, two weeks should be enough time for fermentation to finish.
There are visual indicators that can help you guess when it may be done. One of the most common things people look for are bubbles (or lack thereof) coming from the airlock. That’s a good indication, but it’s only an indication. Because cold liquid holds more CO2 than warm liquid, bubbles coming from the airlock could mean nothing more than the temperature has gone up and the CO2 that dissolved into the beer as it was fermenting is now coming out of solution. A lack of bubbles can also be caused by a bucket fermentor lid that isn’t tightly sealed, in which case CO2 will escape from the lid rather than the airlock. An absence of bubbles isn’t meaningless, but you need to look at other things to be certain it means what you think it means.
Another sign fermentation might be over is the lack of kräusen. Kräusen is the foam that forms on top of the beer as it ferments. As fermentation proceeds, you’ll see the kräusen build up and then slowly recede. So, if it’s been two weeks, the kräusen has fallen, and there are no bubbles coming from the airlock, there’s a good chance your fermentation is finished and you should take a specific gravity reading.
Some software will try to predict what your FG should be. It’s only a semi-educated guess on the part of the software since there are so many things that can influence your FG, but it does give you a target to shoot for. Don’t get hung up if you’re a few points under or over the predicted target. Given what the software is trying to do, that’s darn good!
The next thing you have to decide is whether you want to do a “secondary fermentation.” This used to be the norm for homebrewers, but not so much anymore. The idea is that you transfer the beer to another fermentor (the secondary) and let it sit for a while to clarify and “clean up.” In truth, any clean up should happen during active fermentation while there’s food for the yeast. Clarifying is directly related to time, so if you simply let the beer stay in the primary fermentor for longer, it will clear as well as if you had moved it to a secondary fermentor.
Whether or not you do a secondary, you want to make sure to give the beer time for maturation. A few extra days in primary will give time for the reduction of diacetyl and acetaldehyde levels, which will be done by the yeast.
It’s also been thought that you need a secondary to get the beer off the yeast in order to prevent off-flavors. This idea comes from the world of commercial brewing and has little applicability to most homebrewers. In a commercial brewery, tall narrow cylindroconical fermentors (CCFs) are used. This means that there is a large column of liquid (which is heavy) sitting on top of the yeast. The pressure from this column of liquid could theoretically cause yeast cells to rupture and off-flavors to form. In order to prevent this, CCFs have valves on the bottom that allow yeast to be discharged. The homebrew version of this concept (unless you’re one of the people who has a CCF at home) is to simply remove the beer from the yeast by transferring to a different fermentor.
Except … we don’t use tall, narrow fermentors that apply thousands of pounds of pressure to the yeast. We generally use buckets or carboys, which are short and wide in comparison to a CCF. So, the need to transfer to get the beer off the yeast is lessened. (Although we do still recommend not leaving the beer on the yeast for more than a month or two—your beer needs to be enjoyed after all!) In addition, perhaps most importantly, yeast health these days is far superior to what homebrewers used in the “olden days” and strains are far less susceptible to ill effects, not in small part due to the improved quality of packaging. As we stated above, good yeast health and all the work we do to maintain it allows brewers to focus on making beer instead of never-ending minutiae.
So, the general rule of thumb is you shouldn’t bother transferring to a secondary fermentor for most beers. Simply leaving the beer in the primary will provide the clarification you’re looking for. (Doesn’t that sound Zen?) If you transfer the beer, you not only waste your time and effort, you run the risk of picking up oxygen, which can shorten the life of the beer, or even contamination. Sure, we know you’re gonna be careful and minimize those risks, but why take a chance with something that’s pretty much unnecessary? And aren’t we trying to make things simpler?
But there are a few times when a secondary might be appropriate. The main one is when you’re adding fermentables, which can restart fermentation due to the sugars they contain. For instance, if you want to use fruit in your beer, the best way to do it is to put the fruit into an empty, sanitized fermentor and rack the beer onto it. Another case where a secondary might be useful is when dry hopping. Certain strains of yeast will interact with hops to create flavors that don’t come from either one alone. This is commonly called “biotransformation,” but that’s a specific term that we can’t use for all of these interactions. There is also evidence that biotransformation doesn’t really exist! Sometimes, these interactions are exactly what the brewer is looking for, like the “juicy” New England IPA style, where much of its unique character comes from the interaction between hops and yeast. (Although even then it seems most of the beneficial interactions arise when the yeast is actively fermenting, not falling out.) For other styles, the interaction between yeast and dry hops is undesirable, so getting the beer off the yeast before dry hopping provides a different, maybe sharper, character of hoppiness that more accurately represents the hop itself.
But if you do or don’t go to secondary, there’s one final step that we think is key to getting the best bang for your buck and it’s as simple as getting your beer ice cold and letting it sit. This is the vaunted “cold crash” and it’s really not that dramatic. Reduce your beer in temperature to, say, 35°F (1.7°C) or thereabouts, and let it sit. Drew does this in a keg with CO2 on top of it to avoid the vacuum factor that the cold crash will cause. (A decrease in temperature means a decrease in pressure in the headspace behind the airlock, which leads to a low vacuum/suck back of the sanitizer in your airlock/blowoff.) The cold crash punches down all the remaining yeast, trub, hop matter, and big gloppy protein strands and forces it all to settle out. Once down at the bottom, assuming you’re careful with your transfers, it will never bother you again! We like it as a gentle clarifying and finishing step. Just turn your fridge/freezer/chamber down as close as you can get to 35°F and leave the beer there for a few days. You’ll be surprised!
Look, we said it at the start of this whole thing and we’ve said it several times since—your yeast health matters. It matters more than anything else you do in the brewery. Even if you have the world’s worst sanitation, temperature control, recipe formulation, and bottling practices, good yeast health can at least get you something drinkable (maybe in the loosest possible sense of the word). If you take nothing else away from all of our blatherings, remember this:
And if all else fails, remember that—almost always—yeast just want to do their job. Let them.
Mark Van Ditta first appeared on the American Homebrewers Association discussion forum under the nom de web “S. Cerevisiae.” It soon became apparent that Mark had a wealth of information about yeast strains and how to use them. But some of the information was controversial because it flew in the face of conventional homebrewing wisdom. Probably the biggest brouhaha came when Mark introduced his advice for making yeast starters. He called it “Shaken, Not Stirred,” also referred to as the “James Bond method” and “SNS.” Rather than using a yeast calculator to figure out how much yeast you needed, putting the starter on a stir plate, crashing the yeast, and decanting the wort (the popular method at the time), Mark advocated for putting a quart of 1.035 wort in a gallon container and shaking it to fill the container with foam. You then pitch your liquid yeast into that and pitch the entire thing at high kräusen the next day.
It sounded like heresy to Denny. Where was all the sciency stuff? But somewhere in the recesses of Denny’s brain, something clicked for him. This was a lot like the starter method Denny had used when he first began using liquid yeast, before yeast calculators and stir plates. And he recalled how effective that method had been.
Denny gave the SNS method a try. The first thing he noticed is how fast and easy it was compared to the stir plate method he had been using. And wonder of wonders, the beer was every bit as good as when he used the more laborious starter method! Denny has now been doing it this way for so long that he doesn’t even know where his stir plate is anymore!
We asked Mark to give us his thoughts on yeast. Here they are, in his own words:
I taught myself most of what I know about yeast. Quality brewing yeast was difficult to obtain when I started to brew in early 1993. I caught the bug after culturing yeast from a bottle of Sierra Nevada Pale Ale. Brewing with that culture was a light-bulb moment for me. I learned how to plate and prepare sterile media in high school, so it was merely a matter of gaining access to glass petri dishes, screw cap culture tubes, and agar. From that point forward, I brewed with cultured yeast that I maintained on agar slants. While a lot of my early yeast strains were isolated from brewery samples, it helped that Jeff Mellem and Maribeth Raines started BrewTek around the same time. BrewTek was a fantastic resource during the early days of the home brewing revolution. Working with their mini-slants improved my yeast culture transfer technique. BrewTek’s mini-slants were so small that subculturing new slants and propagating stepped starters from 16 x 100 mm glass culture tubes was a breeze.
After I mastered maintaining a yeast bank in a home brewery environment, I decided to delve into microbiology and biochemistry. Interest in yeast genetics and molecular biology came later. I basically had to teach myself all of these disciplines. My ex-wife was a laboratory biologist when she first started her career. She was amazed that I was able to teach myself these subjects, especially organic chemistry. However, I have always found it to be easier to learn challenging subjects that have practical applications. Surviving graduate school in a STEM discipline also helped. One of the things that one learns in graduate school is how to read and decipher scientific publications. Writing about yeast reinforced what I knew. One needs to truly understand a topic in order to present it in a way that most people can grasp. The problem with scientific publications is that they are written by PhDs for PhDs, and most people are not PhDs.
In my humble opinion, amateur brewers tend to overthink yeast, especially when it comes to starter size. Yeast cultures grow exponentially; therefore, they are a like nuclear weapons in that close is good enough. The yeast cell population doubles every ninety minutes until the medium is exhausted or maximum cell density is obtained. After reaching maximum cell density (approximately two hundred billion cells per liter), additional cell production is for replacement only.
What is important when creating a starter is that the cells that end up being pitched into the fermentation have good ergosterol and unsaturated fatty acid (UFA) reserves, because the pitched cells will share these compounds with every one of their descendants. We need to remember that ergosterol and UFAs are produced in the presence of dissolved oxygen (O2) during the lag phase; therefore, it is important to saturate the starter medium with O2 when the culture is pitched. The SNS starter method is little more than a low-tech way of maximizing dissolved O2 when the culture is pitched due to the fact that foam provides a large surface area for O2 pickup.
A lot of brewers wait until a starter ferments out, but that is too long from my experience. A culture should be pitched at high kräusen. That is when the culture is making the transition from the exponential growth phase to the stationary phase. The quality of the cells declines after a culture transitions into the stationary phase due to mother cells being replaced by daughter cells with lower ergosterol and UFA reserves. Allowing a culture to ferment out and enter quiescence can result in pitching cells with significantly lower ergosterol and UFA reserves. Pitching the cells at high kräusen into freshly aerated wort shortens the lag phase and maximizes the use of dissolved O2. Ergosterol is the plant equivalent of cholesterol, and while we only hear negative things about cholesterol, it is needed for things like brain health and hormone production. Ergosterol and UFAs keep the plasma membrane in a yeast cell pliable, which, in turn, makes it easier for a yeast cell to take in nutrients and expel waste.
Sanitation is the most critical thing to remember when starting yeast. Most infections are pitched with the yeast culture. A brewer wants the pitched yeast to be the dominant organism in the fermentation. That is why viable yeast cell counts are emphasized in brewing texts. Bacteria cells double in one-third the amount of time that it takes for yeast cells to double, which means that a bacteria culture grows by a factor of eight every time a yeast culture doubles. The yeast cultures available to brewers today contain so many yeast cells that a culture usually only has to double one or two times before reaching maximum cell density in a one-liter solution; therefore, the purpose of a starter is to bring the cells out of quiescence and allow them to build ergosterol and UFA reserves. Most of the time that elapses between pitching a culture and a starter reaching high kräusen is spent in the lag phase where the culture is adjusting to the medium and using dissolved O2 to produce ergosterol and UFAs.
If a brewer keeps things clean, resists the urge to tamper with a starter while the culture is growing, and pitches at high kräusen into well-aerated wort while being mindful of sanitation, they will be rewarded with a healthy fermentation almost every time. We have to remember that we are dealing with biological organisms that convert wort to beer. Some yeast strains are more temperamental than others, so things do go wrong from time to time. It helps to keep notes about the progression of fermentation when working with a new strain. While I am currently on an indefinite hiatus from brewing, I always keep a handwritten log of all of my culturing and brewing-related activities.
1 Episode 24 - We Answer Many Of Your Questions,” September 28, 2016, Experimental Brewing, podcast, 1:40:44, https://www.experimentalbrew.com/podcast/episode-24-we-answer-many-your-questions.
2 S. cerevisiae, January 14, 2015, comment on Philbrew, “Right RPM for stir plate?” https://www.homebrewersassociation.org/forum/index.php?topic=21705.msg275578#msg275578.