When the lagering process has begun, the accepted rule is that the temperature should be at 33-34 degrees for a month or more. My chest freezer and ranco controller will turn on until the target temperature is reached, but the temperature often dips lower than that and then slowly climbs back up.
I ran a test on my setup at 48 degrees with a 3 degree differential. At 51 it would turn on the compressor until it got to 48. It would turn off at 48, but it would go down to about 43 before it started going back up. This was the ambient air temperature and not the liquid temperature, but still, if 33 is the target temperature, and it dips to 28 or so before it starts climbing, won't the freezing temperatures harm the batch? Has anybody lagered and ran into this problem?