"guava paste" -- sort of like guava jam or jelly -- is a favorite filling for hispanic pastries here, pasteles de guayaba. I love them, delicious and no fermenting guava smell. It's such a distinctive odor, nothing quite like it. A story, if you'll indulge me for a minute... years ago, while I was living in Michigan, I decided to drive to Ann Arbor to attend an event at the University of Michigan's botanical conservatory. Dead of winter, mind, but the place was full of inviting tropical greenery (which I missed terribly). Got there and decided which hall to visit first, walked to the door and as soon as I had the door open a crack -- not more than half an inch! -- I said, "there's a guava tree in there!" I hadn't smelled fermenting guava fruit in a decade or more, but I knew it immediately. Sort of like Proust and madeleines, no?