In a previous post I suggested that, at the point of urgently scribbling down that new idea, it may be worth exploring what actually prompted it.
The power of olfactory stimuli in activating memory is well known. I believe it is much harder to ‘dream up’ an olfactory experience than a visual or auditory memory that might affect the character in your story. For a visual stimulus we have Art to display ideas, perspectives, narratives, symbols. We have Theatre and Radio to present ideas and emotions through sound patterns, speech or music.
There is no equivalent for smells. The writer may sit, pen raised, summoning up exactly the right sound or sight to cause his hero to pale with emotion, and the reader to imagine this accordingly. Far more difficult to write more than ‘the smell/scent/perfume/stink of’ (whatever) caused the emotional impact. How much of a struggle to work out what might have been recorded in long term memory.
It might be a good idea to be prepared for that blank moment. Perhaps the answer is to note down your own strong reactions to any smell, pleasant or unpleasant, listing the source for each but avoid the obvious like dog poo. For instance, the whiff of musty clothes in a charity shop reminds Kara of a down-at-heel great aunt; the scent of aloe vera takes Anna back to the birth of her baby but reminds Dan of a little lane in Almeria where he was set on by teenage thugs.
With such a list of smells, you can google them to add any interesting facts to their source and the memories they evoke for you. Easier then to strengthen your writing with that detail that enthralls readers and brings them right into your story.