Just how important is your fermentation temperature in homebrewing? I came across a startling result from an experiment reported in the new homebrewing book Yeast, by Jamil Zainascheff and Chris White.
Chris White is the President of White Labs, a brewer’s yeast manufacturer. White Labs conducted a study in which two of the exact same ales were brewed, except one was fermented at 66°F and one at 75°F. They then tested for the difference in flavors.
Most of the flavors that we’d consider “off-flavors” showed a moderate increase, but what was really startling was the increase in acetaldehyde, which gives beer that green apple flavor.
Its concentration was 8ppm in the 66°F beer, but 152ppm in the 77°F beer. So a 9 degree increase in temperature, but the acetaldehyde was 19x higher!
Controlling Fermentation Temperatures
I’ve known for some time now that fermentation temperatures are important, but over the past year have realized just how important they are. Examples like the one above, plus other information in this book, advice from other brewers, and most importantly, my own experience has taught me that if you want to make the best beer possible, you need to nail your fermentation temperatures.
But that requires equipment.
Putting the carboy in the back of your closet and praying isn’t going to cut it. Even if your house stays at a cool 66°F, during the height of fermentation your beer can easily go up 10 degrees because of the exothermic reactions. And 76°F is going to produce more flavors that will rob your beer of a clean taste.
The good news is that most of these flavors are produced during the first 72 hours of fermentation, so you don’t need to maintain the cooler temperatures the entire time the beer is in the fermenter. In fact, it is beneficial to let the temperature rise after fermentation so they yeast can fully attenuate and clean up some of those flavors produced during the height of activity.
Those first 72 hours is where the magic happens though, and we need to make sure we hit the correct temperatures.
Eliminate Off-Flavors and Control Your Fermentation Temps
Temperature control gadgets truly run the gamut in the brewing world. From a chilly corner in a homebrewer’s basement, to glycol cooling jackets on a commercial brewery’s stainless steel conical tank, to everything in between.
When it comes to controlling temperatures, there is certainly more than one way to skin a cat, but I’m going to look at the most practical options for homebrewers.
The swamp cooler is one of the cheapest and easiest ways to cool your fermenter. There are a few different swamp cooler variations.
Most consist of a container to hold water and require the brewer to continuously rotate frozen water bottles for cooling. A t-shirt over the carboy can be used to draw water up, and some people point at fan at the fermenter to get the evaporative cooling effect.
As you can read in my swamp cooler experiment, keeping consistent temperatures is the biggest problem. Large temperature swings are inevitable unless you are able to rotate bottles in every few hours.
Even if you had that kind of freedom it would be a pain in the ass.
A more advanced swamp cooler I’ve seen uses an Igloo cooler with a foam top. This is a huge improvement because insulation is the weak point of the swamp cooler.
YooperBrew over on HomebrewTalk has has one of these swamp coolers which she calls “The Lagerator”. This is a future project for me.
- Good way to combat the heat of the summer
- Ability to get beer to ideal temperature range
- Labor intensive because you must frequently rotate out frozen water bottles
- Difficult to maintain temperatures
- Lagering is very difficult
For a little bit of an upgrade, this one does the same trick:
Son of Fermentation Chiller
This contraption is one of the most common homebrewer DIY projects out there.
Commonly referred to as the “Ken Schwartz Son of Fermentation Chiller,” it seems that Mr. Schwartz originated this thing.
Here is the original document which is often referenced for plans. How does it work? Schwartz say it best,
The Fermentation Chiller is an insulated box which uses ice, a thermostat, and a small fan to accurately regulate the temperature of a fermenter. While simpler insulated boxes and other simple temperature-management techniques often work reasonably well, they can’t regulate the temperature; they can only cool to “some point” below ambient, which changes as the ice melts.
So basically, you place gallon jugs of ice into the “ice chamber” and when the thermostat says it is time for cooling mode, the fan cuts on and blows cold air into the fermentation chamber until it is at the desired temperature.
The obvious drawback about this is the work involved. The other is that it still involves rotating bottles of ice, but it is much more infrequent (every couple of days) vs. the swamp cooler (every few hours).
- Cheap (~$70) compared to a freezer or refrigerator
- Small footprint (2’x3′) and lightweight
- Very low cost of electricity
- A bunch of upfront work needed, not to mention craftsmanship and tools
- Requires exchanging of ice.
For those looking for a more automated approach, you will want to go with a chest freezer or cooler.
I personally prefer chest freezers (keezers) because their design makes them more energy efficient (the cold air stays inside when the door is open).
Their drawback is that it takes more lifting to get fermenters inside.
These devices must be used in conjunction with a temperature probe and thermostat to control the temperature, which usually cost between $60-$100. Prices for the chest freezers vary based on size and condition. You could easily find a small cheap one on Craigslist for $50, or pay $400 for a large brand new model. T
he added benefit of this option is that now your fermentation chamber can double as a kegerator. That’s a big plus in my book. You’ll need to setup a controller to heat or cool it though.
- Very little construction and maintenance involved
- Keeps the most accurate temperatures
- Can double as a kegerator
- Expensive ($100-$300 for the appliance and $60-$100 for the digital thermostat)
- Large and difficult to move alone
- Higher electricity cost
But I can fit 3 of these Fermzilla’s in my chest freezer. Just Sayin.
Of course you can get a stainless steel Conical Fermenter and shove it in a cooler, keezer, or other DIY temp controlled fermentation chamber.
Or you can pull out your checkbook and get a big boy Conical Bundle.
That’s a wide range of different fermentation chamber options to keep your homebrew from overheating throughout the process.
Now, let’s get to annother very common question when brewing at home:
Do you need a secondary fermenter?
So I had this batch of beer, it’s been in the primary for seven days and conventional homebrewing wisdom tells me that I should transfer it to a secondary. And even today, that’s really what most homebrewers do.
They don’t even question it. You do a primary and then a secondary.
But recently there’s been a shift in the home brewing world and I agree with it. It’s that you should do instead an extended primary and no secondary at all. So in this video (above) I’ll state my case and you can decide whether or not you agree with me.
All right. Now let’s talk about why this theory for a secondary is even out there. But first I want to address the term secondary fermentation cause that’s really a misnomer.
When you transfer the beer, there’s not a new or secondary fermentation taking place. It’s the same fermentation. So we really shouldn’t be using that term. But you really shouldn’t even transfer the beer during fermentation anyways. You should always let that finish in the primary. Just let the yeast do their job and leave them alone.
But assuming you do that, then do transfer to a secondary. That’s the big question and a main argument by homebrewers forward is for clearer beer.
They want to have crystal clear beer, but myself and tons of other home brewers can tell you from experience that we get really clear beer by doing an extended primary and no secondary.
The reason is when you leave it in the primary for a long time, you get this really compact dense layer of yeast and trim on the bottom and then when you go to transfer the beer, you just stop siphoning before you get to that layer and that stays behind.
Even if some gets over to the bottling bucket, that’ll drop out and he can leave it behind in the bucket. Or if someone gets over to the bottles, when you chill the bottles down, that troop will drop out and you just leave that behind when you pour out the bottles. So the whole clarity issue and that argument doesn’t really stand up.
Another argument for the secondary has been that you need to get the beer off the yeast because otherwise you’re going to get off flavors and autolysis is the common one that’s thrown out there and that was true 10 years ago when the only yeast available to homebrewers was really low quality, weak yeast that would die off easily in the beer, but that’s not true nowadays.
Now we have access to really high quality yeast, the same stuff to pros use. We’re making yeast starters, it’s healthier and you can leave the beer on the yeast for an extended period of time.
I’ve gone a month or more and other homebrewers have gone much longer than that and it’s actually good for the beer. Even after fermentation is done. You want to leave it on the yeast because the yeast is going to clean up some off flavors and give you a cleaner, more polished beer.
So that argument doesn’t really hold up any more either. In addition to those things, there are also some risks associated with transferring to a secondary.
Whenever you do that, no matter how good you are at siphoning, you’re going to pick up some oxygen and that’s going to affect the stability of your beer is going to have a shorter shelf life and it can give you some oxidized flavors as well.
Also, whenever you transfer, whenever you open up your beer and you handle it, it puts it at risk for contamination, so when you transfer to a secondary, there’s always a greater risk that you’re going to infect your beer.
So what do I do?
I do an extended primary for two to four weeks, two weeks as a minimum. Even if fermentation is done, I want to keep the beer on the yeast so the yeast can clean up those off flavors.
I know it seems like I’m all against secondaries, but I actually do use them sometimes if I’m doing something special like adding fruit or Oak chips or dry hopping, then I’ll use a secondary or from aging a beer for a few months, a big beer or from lawyering, then I’ll transfer it from the primary.
But what I recommend to brewers and especially new brewers is as your default method, do an extended primary and no secondary.
Then later on, once you get some batches under your belt, decide if you want to add a secondary and see how that works for you. Some homebrewers swear by it. It’s not my preferred method, but of course your mileage may vary, so hope that helps.
So where do I stand in this sea of options? Unfortunately I’m not as sophisticated as I would like. I’m still using my ole’ blue tub as a swamp cooler, which allows me to mitigate high temperatures, but not get the consistency and accuracy that I would like.
The chest freezer fermentation chamber is my goal, and here is how to build a cool looking Keezer that makes for a great centerpiece in the mancave.