Pilsner lager fermentation temperature control

Autumn, Winter, and Spring in the Pacific Northwest are pretty much one season: the season for making lagers in your garage. Daytime temperatures usually range from 40 ºF to 50 ºF, and lows are not much lower. This range is perfect for fermenting lagers with just a heat blanket and temperature controller to ward off the chill. And if the rare day of warmer temperatures arrives, a couple of ice packs around the carboy will keep the beer from overheating.

Eventually, at least most years, the tilt of the Earth begins to bring more of the sun's warmth back to a more Ale friendly temperature range - into the 60s and 70s ºF. During this brief time of year (some call it summer), cooling to lager fermenting temperatures with ice packs becomes impractical. The easier way to keep lager yeasts happy is to move them to a chest freezer.

Example: A German Organic Pilsner based on Jamil's Myburger recipe

Amazingly flavorful German malt ready for an Organic Pilsner.

You've chilled to 70 ºF and racked your gyle off any residual hops from the kettle boil. You've further chilled the gyle to 40 ºF in your chest freezer and racked off of the precipitated cold break material into a 6.5 gallon primary fermenter. You've oxygenated the gyle for sixty seconds and pitched the decanted three liter stir plated yeast starter. Now you need to control the temperature for an ideal fermentation.

A whopping-big 3L yeast starter starts to boil, er, double boil.

Start by wrapping the 6.5 gallon carboy in a heating jacket. (I use a luggage strap to hold the jacket in place around the fermenter.) And since there is likely to be a lot of yeast activity at the start of fermentation, I plug the carboy with my modified 1" blow off tube drilled to hold a thermowell.

Blow-off tube drilled for a thermowell.

Now you can use two temperature controllers to regulate heating and cooling. Put one probe into your chest freezer (set to smallest amount of cooling) and set it's controller to cool within one degree of 40 ºF. Put the other probe into the drill modified thermowell, plug the heat jacket to its controller, and set to heat within one degree of 40 ºF. Over the first 48 hours of fermentation work the temperatures gradually up to 50 degrees. Then you can hold heating and cooling to right around 50 degrees till fermentation subsides. Diacetyl rest - same thing - raise both controllers to 68 ºF for a couple of days, then drop back to 50 ºF to finish.

Dueling temperature controllers - 40 ºF warming on left, 40 º cooling on right.

For the lagering stage take away the heat jacket and warming controller. Put the cooling controller's probe into the fermenter's airlock thermowell and dial down the freezer temperature to 32 ºF in no more than 4 ºF per day increments.