So my first batch (an ESB) has been in the fermentor for just over 48 hours and I'm not seeing any action in the airlock. I'm just being paranoid right? First batch jitters? My volume was a little high (closer to 6 gallons than to 5) so I'm wondering if I under pitched.
Also, when should I take a gravity reading? Thanks.
Typically, you should take a gravity reading immediately before you pitch your yeast (after the wort has been chilled to pitching temperature) to get your OG (original gravity). After you've pitched the yeast, it's best to just leave the beer alone for about a week before checking the gravity again.
Don't worry about lack of airlock activity, but if you're not seeing any other tell tale signs of fermentation (especially some sort of krausen buildup on the side of your fermenter), then it's possible fermentation never got started.
As a few others have noted, it'd be helpful to know what yeast you're using, your fermentation temperature, your pitching temperature, how much yeast you pitched, your aeration technique, etc.
Oh, and if you used the same amount of extract/grain as the recipe called for and just put in too much top off water to end up with 6 gallons instead of 5, then all you really would have done is lowered your original gravity (i.e. you diluted the wort). The amount of fermentable sugars available to the yeast would remain the same as what the recipe called for, so as long as you pitched the amount of yeast the recipe called for then you probably didn't under pitch.