Originally Posted by Finster4
A digital thermometer will give you a good referance, but your going to need the liquid temp.
Yep, the air temp will fluctuate a lot, so you want to measure liquid temp will stay more stable and represent the actual beer temperature.
One common approach people take is to take a white labs yeast vial (or other small container) and fill it with the gel goo from an ice pack, drill a small hole in the cap and jam the thermometer probe in there. If you're only looking for a quick way to check, a glass of water with the probe in it ought to work just fine.