Aurora, I guess you had missed the cutscene at the poor quarters, quarantine section (Elrath came out). The soldier you speak to should have told you were E. normally lives. On entering his house (after getting the harvest quest, finding the barrels, speaking to barman Splinter, reporting to Hugh!!!) there should have been a speech option with E. about a stolen key.
But it's just a small side quest - same goes for the grain bill - you still can enjoy Penumbra <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
Kiya