Brewers have been known to ferment saisons as high as 115F. I don't know how the yeast are still alive at those temperatures but it works because there are commercial brewers doing it. Saison yeast can ferment in the 60s and 70s and some brewers prefer those temperatures. Personally I prefer a warmer fermentation to drive more assertive fruit character. I find cooler saison fermentations produce a little more spice but a blander flavor. In particular, I find the Dupont strain produces a very bland, muddy flavor in the 70s. It really needs to get into the 80s to push out great flavor. WY3711 is probably the most forgiving because it doesn't produce muddy flavors at any temperature and it lacks the stalling that the Dupont strain is well known to cause. (Not to mention the Dupont strain's harsh flavor early on that needs weeks of cold conditioning to mellow.) The common approach for a warm saison fermentation is to start in the upper 60s to mid 70s and let it free rise into the 80s (or higher). The cooler fermentation allows the yeast to get acclimated and start fermenting without the stress of warmer temperatures. That can help avoid fusels and other off flavors common to a stressed fermentation. High levels of oxygen and nutrients can also help avoid off flavors.
In Texas it gets hot enough during the summer, and in most years all the way through the fall, to ferment saisons by starting them off at ambient temperature and moving them to a garage to rise into the upper 80s or 90s. It's around 100F out today so the garage won't be far behind. This isn't a bad strategy, certainly this is the way rustic operations would have to ferment. However, letting nature set fermentation temperature means inability to obtain consistency, dial in a flavor profile, and risking the beer not getting warm enough or getting too warm. Like a cool fermentation, controlled fermentation temperature is key to getting consistent and repeatable results. So I set out to find a way to create a controlled but hot fermentation.
Of course, some of you live in cooler climates where you have the reverse problem of trying to get your beer to stay warm enough in the 50s and 60s during many parts of the year (and I am very jealous). If if that is your "problem" you can also use a heating element to obtain consistency at those cooler temperatures.
I started off with my fermentation chamber (fridge) and Johnson digital controller. Not only is this digital controller awesome for controlling cool fermentations, it can be set to work in reverse by moving a couple jumpers inside the unit to turn on when the temperature gets too cool so it will activate a heating device. It's a screwdriver and pliers job, so a very easy modification even for people like myself who lack technical skills. I wanted to incorporate my fermentation chamber because it would provide an insulated space that would keep warmth inside and provide a more consistent process.
I rejected a couple heating options that I have seen other homebrewers employ. Some homebrewers use heating blankets duct taped to their fermentors and plugged in to a temperature controller. I am sure this method works but I rejected it for a few reasons. First, I don't own a heating blanket, so that meant buying a $15-20 blanket that I probably wouldn't use for any other purpose. Second, most blankets now come with automatic timers, which means the blanket might shut off before the desired temperature is achieved, which makes creating a consistent process more difficult. Third, heating blankets are prone to starting fires and I have no interest in keeping a fire hazard plugged in and running for days at a time. Next.
Another method commonly employed is using a heat lamp, or even a regular light bulb, controlled by a temperature controller and put inside a small fermentation chamber. This idea wasn't bad except I wasn't thrilled with the idea of exposing my beer to that much light. I could have created a shield on the light but that seems like it would also shield some of the warmth from the beer, making it an inefficient solution. Additionally, it seems like a fire hazard letting a heat lamp run all the time in a fridge. I know people run heat lamps on reptile cages but I wasn't sure whether running it on a temperature controller would create a fire risk or reduce the life span of the bulb by flipping it on and off. I also suspect that it would be harder to get a larger batch warm off a light bulb in the same way as a small batch, which meant introducing a risk of inconsistency. Next.
I also considered a brewbelt, which is a small belt-like device that straps on to any fermentor and can be run
off a temperature controller to apply direct heat. I liked this idea because it would provide direct heat to the fermentor and that would allow better control and more consistent results. The price on the brewbelt is fairly reasonable around $23 so long as the product has a long life. The reviews I read online were not terribly positive. Many indicated an inability to maintain consistent temperatures and that they died after a couple years. There were also suggestions that the belt would create a hotspot on glass that could lead to weakening the glass. That's a problem for my one gallon batches since I brew those in a 5L jug. (Although I would think if it's hot enough to weaken glass it would be hot enough to have a negative effect on plastic as well.) Next.
Most of the brewbelt critics referred people to another product called fermwrap. Fermwrap is similar in design to the brewbelt except it is a larger strip of heating element where the heat is channeled through two strips, reducing the probability of a damaging heatspot. It is commonly used on both plastic and glass. The larger heating surface allows more consistent heating, which is also a plus. Additionally, I did not find reviews claiming a short lifespan. Sounds great although the price was around $28 and it seemed a little large for my 5L jugs.
Reptile Basics, who sells flexwatt along with the power cord and connectors. They will even connect the power cord to the flexwatt tape for free. They will cut the length of the tape to your needs. Best of all, they offer multiple widths, so I was able to purchase the six inch tape for my 5L jugs and a separate twelve inch tape for my bucket. For $25 I was able to buy a separate flexwatt heater for my 5L jugs and one for my fermentation bucket (with shipping). The construction is solid and they shipped my order within days. I highly recommed doing business with Reptile Basics.
Once I had all the parts I just needed to get everything put together and test it out. Like fermwrap and brewbelts, flexwatt needs temperature control to shut it off when the desired temperature is reached. Otherwise it will just keep pumping out heat. I don't know how hot it could get the beer but the whole point of this project was to get consistent heating. I expected to see about a ten degree increase, which was a concern since my beer was running at ambient temperatures in my fermentation chamber at 75-78. However, I hooked up the flexwatt tape on my 5L jug with a couple small pieces of duct tape and let it rip. Within a couple hours it was up to 90, where I set the tape to cut out. Perfect. I'm not sure if it would run as efficiently or get as warm if I left the fermentor out in the open room so the fridge's insulation is helping save electricity and produce consistent temperatures. I suppose wrapping the fermentor in a blanket or sleeping bag would work but I have a fear of creating fire hazards by putting flammable cloth against an electrical heating element.
It's definitely weird to touch a fermentor that is warm but it is getting the desired results. Overall, I am extremely happy with this set up. The flexwatt tape gets warm but even while running the heating elements are not so warm that they are uncomfortable to touch. If I had to guess just from touch I would say the tape itself is a few degrees cooler than my body. That's a very safe temperature for glass and plastic alike. Definitely the best route to get a warm fermentation with consistency.
I've since read people trying ceramic heating elements and aquarium heaters. Personally I would be careful with ceramic heating elements because they can get very hot very quickly and that could create a fire hazard along with wild temperature swings in your beer. With the aquarium heaters I have to imagine people are not putting them directly in the beer but instead in a tub of water with the fermentor inside. That's not a bad path as long as you can get good results although the aquarium heaters are a little more expensive than the flexwatt tape option.