Controlling fermentation temperature is one of the best ways to brew better beer. Here are a few reasons why.
Keeping the temperature consistent throughout fermentation will keep those yeasties hard at work. Variations of even a few degrees during the day can lead to under-attenuation or a stuck fermentation.
The fermentation process also generates heat – which can raise the temperature inside the fermenter several degrees. When the temperature gets too warm the yeast will begin to produce excessive amounts of fruity esters and fusel alcohols – those hot, solventy alcohol flavors. Keeping the temperature closer to the low end of the yeasts’ fermentation range will generally give you a cleaner flavor in the finished beer.
So how do we keep those temperatures in the optimal range?
At the high end there are insulated conical style fermenters with integrated heating and cooling units. These are much like the ones you see at a commercial brewery – but they’re expensive – $1500+ for a fully kitted out one.
The next best choice is a spare refrigerator or freezer with an external temperature controller. The controller has a sensor which monitors the temperature of the beer and overrides the thermostat on the freezer to keep a very exact setting – some models work with a +/-1º range. A used freezer or refrigerator can often be found on craiglist for under $100 and the temperature controllers are about $75-150 depending on the model and options.
But what if you don’t have room for an extra refrigerator or its still a bit too much money? Here’s a simple alternative that works exceptionally well at holding a steady ale fermentation temperature and won’t break the bank.
- A large tub – The 18 gallon model pictured above was $6.99 at Target
- An adjustable aquarium heater – Get the one with the largest temperature range you can find. This one was $24.99
- An extension cord – In case there is no outlet nearby – $5.99
- Stick-on liquid crystal thermometer – $3.99
Optionally – you might want to add a second heater, or a small aquarium pump – to keep the temperature of the water in the tub the same all over.
Start by placing the tub in a cool dark place. A spare bathtub works well. When you’re done brewing – place your fermenter in the tub. Stick the liquid crystal thermometer to the side of carboy just below the top of the wort.
Fill the rest of the tub with water at roughly your desired fermentation temperature. Don’t fill the tub completely – stop before you get to the thermometer. It will de-laminate and fall apart if left under water for too long.
See the picture if any of that didn’t make sense.
Add the aquarium heater – it should have some suction cups or something to hold it in place. Set the thermostat dial a few degrees below your target fermentation temperature – its better to warm it up a few degrees if its too low than to cool it down from too high.
A towel or a t-shirt wrapped around the top of the fermenter will wick up some extra moisture and improve the cooling a bit – and it will help to block out light as well if your fermentation area isn’t completely dark.
The temperature you set on the thermostat probably won’t match the temperature of the wort exactly, so be sure to check it after about 12-24 hours. Don’t mess with it too much – it will take a couple of hours for the wort to respond to any adjustments. Once you have it “dialed-in” you can mostly forget about it.
The increased thermal mass of the water in the tub combined with the wort will help to eliminate the effects of temperature changes throughout the day and the fermentation cycle. The evaporative effect will keep the temperature of the water several degrees below ambient.
This setup should let you ferment at pretty much any ale temperature from 65-80ºF. You might get it to go a bit lower – or a bit higher depending on the ambient temperature in the room. A small fan blowing continuously at the fermenter can also bring the temperature down a couple of more degrees.
If you’d like to ferment at lager temperatures – around 50ºF – you could try using an insulated cooler instead of a tub and adding some frozen 2-liter bottles of water. The bottles will need to be changed frequently – so its more labor intensive and more difficult to hold an exact temperature. I never had much luck with this method – but lots of other people do.
So there you have it. An easy way to improve your beer without lots of extra equpiment, that doesn’t take up too much space and at a reasonable price.