I have to keep track of several temps when i get a beer down this cold. I don't have an automated temp control system yet, so everything is done manually and tested on water-only batches before subjecting beer to these measures.
Winter in Minnesota is great for lagering, as long as you have a well insulated place to store your beer. Fortunately, our garage is very well insulated, and can maintain a temperature above freezing with just a little oil-filled electric heater I got for $4 at a yard sale.
- I keep the garage at about 40F / 5C
- I keep the yeast fridge at 35F / 1.5C
- I keep the lager fridge at about 30-31F / -1C
The problem with Fermometer brand thermometer strips is they only go down to 36F, so while your Pilsner may spend a couple days in the 60-70F range, most of its life is lived off the scale. So i trust my swanky 1970s analog readout, which is surprisingly quick adjusting.