If you can afford it, the best temperature-control option is, no doubt, the purpose-built fermentation tanks with precise temperature control. You can purchase a stainless-steel unitank or conical with a heating pad and cooling coil for right around $1,000 (equivalent to the cost of a few dumped/mediocre batches of beer). The market also has different types of chilling/heating rods that can fit right into your existing fermentors for only a few hundred dollars. If you’re reading this thinking to yourself, “The best cheap lagering option is to find a cold corner of your basement and put a wet towel on your fermentor,” then you’re targeting a different level of consistency and control than I am.
For those who are working on a tight budget but desire some level of precision, I recommend a temperature-controlled chamber. The easiest form is a chest freezer or a refrigerator, both of which you can get for $10 (used) to $150–$200 (new from Home Depot). From there, you just need to get a $22 temperature controller that cycles the power of the chilling chamber on and off based on a temperature probe. Should you choose to go this route, here are some tips:
If your chilling chamber is a freezer, don’t put the temperature probe in the fermentor (in the liquid or the temperature-probe port). The heat transfer between your beer and the air happens slowly enough that the ambient temperature of the chamber will drop to -20°F (-29°C) before your fermentor gets to 55°F (13°C), and then it will continue to chill your beer much lower than that. I prefer the chamber temperature to slowly equalize with the wort/beer temperature rather than trying to rush it.
Be aware of the energy/heat created during fermentation. During active fermentation, I typically set the ambient chamber temperature a couple of degrees lower than the temperature I would like the wort/beer to be. I recommend putting a temperature gauge on your fermentor so you can see the delta between the air temperature and your fermentor during the stages of fermentation. You will have to tweak this based on the voracity of your yeast cells and the vigor of your fermentation.
Be aware of the location of your chamber. The inside walls and floor of a chest freezer get very cold, so make sure you lay down a couple of 2×4s or something else that doesn’t transfer heat to get the fermentor off of the ground. The same for the inside walls—keep the fermentor off of them.
If you use a chest freezer, remember how heavy those fermentors are. Can you easily lift a 60 lb (27 kg) wet glass jug? Consider using a stainless bucket with handles.
While this method works pretty well, there are some downsides to the temperature-controller/cooling-chamber method:
- There is only one set temperature for your chamber, so if you want to lager one beer and free-rise your IPA to 73°F (23°C) at the same time, you’re in a tough spot. It’s tough to access a sampling port for gravity readings and tasting. You’ll disrupt the trub cake when you move the fermentor out of the chamber for any transfers or packaging.
For the modest price of 1–2 dumped batches from your wet-towel method, you can make yourself some fine brews using a temperature-controlled chamber. That being said, there is no substitute for spending a little bit of extra money up front on a chilled/heated unitank with sanitary welds. There is a reason that professionals do it this way.