What makes a coffee turn out sour? I've heard a few good things about Intelligentsia coffee so I decided to order some. Once it arrived I tried it in my AeroPress and it turned out very, very sour. (several times)

Steps taken using AeroPress:


rinsed filter
used water that was 1 minute off boiling
brewed for 1:30 total
plunged just until I heard air through the filter


Coffee was so sour I couldn't finish it. Considering that I tried several times and that I've been using the AeroPress with great success for the past few months this has me very curious.

My Question

What makes a coffee turn out sour?
When the water has too short of a time to extract the flavor from the bean.

Try grinding the beans a bit smaller.