I've been searching the archives for this question, but I haven't seen it come up yet so I thought I'd post for responses.
I was doing a brew day a few weeks back with this recipe:
The only change is that I used 6.6 lbs of DME instead of 7 (obviously because of the weight it ships in). Unfortunately just before I was going to take the hydrometer reading, my roommate bumped it, knocking it on the floor where it broke.
as a n00b, I didn't have a backup. Instead I took a sample in the hydrometer tube (which I kept in the fridge) until I could get another one. about a week later I got my new hydrometer. I warmed up the wort in the fridge to room temperature and took the reading. My beer's OG was 1.042. the expected OG is 1.072
The question is -- would there be any reason to think that the reading would be off after a week in the fridge? would some little bacteria been chomping away at the goods?
The main reason I am interested is that IPA's tend to have a high ABV, and I don't want to ruin any of my friends by telling them that it "only" has ~4.5% ABV.
Side notes: I boiled a 4 gallon batch and added 1 gallon of water. I also think that I didn't "mill" the grains with a rolling pin very well (not knowing how to do it well until reading here). These might be factors in the OG.