For every beer brewed, the yeast cells live out a whole series of steps. They wake up, grow new yeast cells, consume sugars, and produce carbon dioxide, alcohol, and a host of other compounds, then drop back into a dormant state and fall out of solution. It’s easy to overstate the extent to which we as brewers actually “make” beer and just as easy to understate the extent to which yeast cells are doing the bulk of the hard work. Yeast, though, works in an environment that we manipulate, and the ways in which we tinker with that environment greatly impact the work that yeast can do within it. One of the key features of that environment is temperature, and good brewers manage temperatures to give their yeast the best shot at producing the beer that the brewers (and, I think, the yeast) really want.
We could talk for days about ideal fermentation temperatures for different yeast strains, but we’re going to keep it simpler than that. We’re just talking about ways to manage temperature, whatever you want that temperature to be. Control is the name of the game for many aspects of brewing, and controlling temperature should be first on your list as a brewer because your yeast’s health, performance, and effectiveness are relying on it. Yeast cells want a steady and productive environment, and that’s just what we should endeavor to give them.
I’m sure that most of you already have a good sense of why temperature management matters in brewing. Yeast will produce different precursors and compounds, consume sugars at different rates, yield different flavor profiles, exhibit symptoms of stress, and attenuate more or less completely depending on the temperatures in the beer as it is fermenting. Temperature will affect how quickly fermentation starts, how long it lasts, and what is left behind. Temperature will increase the risk of off-flavors, decrease the development of esters and phenols, and often will mean the difference between sweet, apple-like ethanol and harsh, hot fusel alcohols. Neglecting the temperature of your fermentation makes about as much sense as not tuning your guitar before a performance. Temperature matters. I’d go so far as to say that nothing matters more than temperature. So, if everyone is sufficiently panicked, let’s get into how you keep it under control!
Temperature and Timing
In the brewing process, there are effectively three stages of temperature control that yeast cells need. There’s getting to the initial “starting” temperature, managing the “fermenting” temperature, and warming things up for the “final cleanup” temperature.
First, you need to get your beer from the “chilled” post-boil temperature down (or up) to your initial fermentation temperature. You do this during the lag phase (when you first pitch the yeast), to ensure that when your yeast starts its exponential growth phase and begins taking up the simple sugars, it is producing what you want it to produce (no more, no less). So, you might be getting your wort down to about 75–80°F (24–27°C) using your immersion or plate chiller, which is a fairly high start even for a saison. If you begin fermentation there, you might end up with a lot of precursors and off-flavors that you don’t want, so you want to cool that beer down to about 70°F (21°C). I’d start even lower, but saison yeast strains tend to be okay at higher temperatures, and this still leaves you room to ramp up. I pitch my yeast at whatever temperature I’m at after chilling from the boil and adjust the temperature to my initial fermentation temperature while the yeast cells are waking up.
Second, you have temperature management during the exponential growth phase (basically, days 1–3) and the stationary phase (days 4–10). During that time, the yeast cells are chewing through a lot of sugar, producing esters, alcohols, and phenols, and they’re also warming up the beer that they’re living in. If you let them run wild, they might move the temperature higher to a level that makes them more likely to produce things you don’t want, or it might create large temperature swings throughout the day that will trick the yeast cells into dropping back into a dormant stage. So it’s helpful to manage their temperature a bit here. The key is to maintain a slow and steady rise in temperature, so that as the environment becomes more toxic (alcoholic) and as the yeast cells start to tire, they keep up a regular and complete fermentation of your beer. So let’s take our fictional saison: You may have started at 70°F (21°C), but you’re not staying there. You hold at that initial temperature for about 72 hours, but then you want to slowly raise the temperature over the succeeding week or so, walking it up to about 75°F (24°C). Feel free to tinker with this, though: your yeast strain choice and flavor preferences may vary, and there’s a lot of play in this one! I know people (my Brewdog, Biscuit, and me) who ferment even their Belgians on the colder side; I start all of my ales at about 65°F (18°C) no matter the style, for consistency. I know other people (including one who works for a yeast manufacturer) who start their fermentations as high as 78°F (26°C).
Different strokes...
Finally, there’s the concluding stage of the fermentation, and here you want to juice the yeast cells into doing a good final cleanup of the beer: reabsorb that diacetyl, process that acetaldehyde, break down those last few chunks of maltotriose, all before drifting back to sleep. For that, you need to bump up the temperature in their environment. I like to add another 3–4°F (2°C) over the course of a day or two and hold it there for a couple of days before crashing to near freezing for clarity.
So, to recap:
- Chill (or heat) to the initial fermentation temperature
- Hold steady there for the first few days
- Slowly raise the temperature to encourage complete attenuation
- Warm up for your diacetyl rest/cleanup
- Cold crash to encourage flocculation and clearing
Practical Temperature Control
In a perfect world, all brewers would own dual-stage temperature controllers and a dedicated fermentation chamber (usually in the form of a chest freezer). You’d brew, pick an initial fermentation temperature, and dial that puppy in to whatever you want as the fermentation process progresses. The cooling mechanism (the freezer’s own compressor) would keep your beer from running away with itself as fermentation starts, while the heating mechanism (often a shielded incandescent bulb or ceramic heat element) would keep temperatures moving upward and stimulating yeast activity as the yeast cells start to slow down.
But let’s face it: Not everyone has that luxury, and that shouldn’t mean that you’re sacrificing beer quality. You should still be managing temperature. The issue is that you can’t simply say, “Oh well, I guess I’ll just ferment at room temperature,” either. Why not? Because there’s really no such thing as “room temperature.” What I mean by that is that throughout the day and night, the temperature in your room (wherever that is) will vary, often by a significant amount. This can cause the yeast to behave erratically. If temperatures are increasing, you might end up with fermentation characteristics or hot alcohols that you don’t want, and dropping temperatures can cause premature flocculation and incomplete fermentation. So if you don’t have that dedicated and controlled fermentation chamber, your goal should be twofold: first, promote a steady temperature; and second, do your best to hit your ideal “phase” temperature.
For steady (and generally brewingfriendly) temperatures, your basement is your best friend. Because the basement is subterranean, its unconditioned temperature will likely be somewhere around 60°F (16°C) almost all year long. And since the basement isn’t directly exposed to the elements, that temperature will remain much steadier than in rooms above grade (many digital thermometers have a high-low setting that you can use to measure the actual variation in any 24-hour period).
Consider your own circumstances, of course, but start in the darkest and most out-of-the-way corner of your basement. Near the walls is great because it’s both close to the source of that steady-state-temperature dirt and out of the way of drafts and currents. If you have a separate closeted sump-pit area, you can even shave a couple of degrees off of the regular temperature thanks to evaporation in the exposed pit area. I had a tucked-away area in my first basement that held a steady 54°F (12°C), and as fermentation progressed I could simply slide the carboy farther out from the corner to slowly raise the temperature. It was perfect!
If you don’t have a basement, don’t despair. There are other options. First, start in the heart of the house. An interior room with no windows will almost always be a better option than a room with an exterior wall. In any room, a closet is going to exhibit smaller temperature swings than the rest of the room, especially if it has a non-louvered door that you can keep closed and no HVAC vents/elements. A large-enough cabinet or pantry can work this way as well. If that’s not an option, you might consider putting your carboy/bucket inside a larger storage container and filling it with water: The additional thermal mass of the water will slow any temperature movement caused by changes in the ambient air temperature (and you can also manage the water temperature to help nudge your beer’s temperature in the direction you’d like it to go). And when it comes to steady temperatures, don’t underestimate the simple things: avoid drafts, sunny spots, commonly opened doors or windows, and exterior walls. Steady as she goes.
But what about active temperature control? There are two common methods for cooling beer, and both are fairly low-tech. The first is a simple water bath. If you want to reduce/hold temperature, drop the fermentor into a water bath, either using the water as is or adding frozen water bottles or jugs. You might also consider a simple evaporation cooler. Place the fermentor in a pan with a quantity of water in the base. Drape a T-shirt, thin towel, or sheet over the fermentor such that it drops into the water and wicks the water up and around the fermentor. As the water evaporates, it will reduce the temperature of the beer in the fermentor—all the more so if you keep a fan on the wet cloth! With either method, I recommend less aggressively managing it at night to better simulate a steady temperature environment (since ambient temperatures will likely fall in the evenings).
When it comes time to warm up your beer (either because it’s winter or because you’re looking to bump up temperatures at the end of fermentation), you have two similar strategies. There’s nothing like a warm bath—and your yeast will provide its own bubbles. You also shouldn’t underestimate the impact of tenting/wrapping your fermentor with towels or blankets, especially if you can direct the warm air from a heat register up under the wrappings (this works to cool beer if the air conditioning is on, too). To this day, I bottle condition beers all winter by simply putting the cases over the vent in my brewery and draping a thick towel over them. Seven days to carbonation!
And by all means, be creative. Just keep the two goals in mind: steady temperatures and timing.
Time and Temperature
Just because you don’t have a temperature-controlled fermentation chamber doesn’t mean you’re out of luck when it comes to temperature control. Beer was made for thousands of years—and grew to its prominence today—before the advent of air conditioning and freezers. Find your own equivalent of the beer caves of Munich, the hot farmhouses of Belgium, or the frigid brewhouses of the Baltic region. Remember, though: your yeast cells likely won’t notice a degree or two of difference here and there, but they will notice significant changes in temperature. Consistency matters more than accuracy. If you can time your temperatures to the appropriate phase of the yeast life cycle, fantastic. But if not, worry more about consistency than absolute temperature.
Slow and steady won the race for the tortoise—it will work for you (and your beer)!