Here's an interesting article on the topic of how the brain processes scent. I sometimes touch on this topic in my classes. It can be frustrating to coffee people when they recognize a smell but can't put a name to it. I always remind people: it's not your fault! It is difficult. Keep trying!
Why is smell so sentimental? One possibility, which is supported by this recent experiment, is that the olfactory cortex has a direct neural link to the hippocampus. In contrast, all of our other senses (sight, touch and hearing) are first processed somewhere else - they go to the thalamus - and only then make their way to our memory center. This helps explain why we're so dependent on metaphors to describe taste and smell. We always describe foods by comparing them to something else, which we've tasted before. ("These madeleines taste just like my grandmother's madeleines!" Or: "These madeleines taste like the inside of a lemon poppy seed cake!") In contrast, we have a rich language of adjectives to describe what we see and hear, which allows us to define the sensory stimulus in lucid detail. As a result, we don't have to lean so heavily on simile and comparison.
Smelling, tasting, and using words to describe the two all at the same time is like trying to play basketball, soccer, and a video game all at the same time. The key to getting "good at smelling" is to practice again and again. And when you try something new and unusual, try to make a distinct memory of the experience (including non-smell things like the people you are with, the sounds and sights, etc).