It has happened to everyone... either while doing a wine tasting or upon entering a room... suddenly you realize: "I smelled a specific scent earlier and now I can't detect it anymore: has it disappeared?" This phenomenon is in great part due to the naming process of habituation that allows our brain to unconsciously "filter" the smells already detected and known, and is probably a primordial defense mechanism. In fact in the human's early days, one of the main uses of the olfactory sense was to smell dangers even before they manifested themselves to the other senses (sight, touch, hearing). It was important to pay attention to "new" smells that had just arisen rather than to other smells perhaps more intense, but already present in the environment (and therefore probably not dangerous because they were linked to a known situation).
This, combined with the fact that we are able to concentrate only on 2 or 3 smells at a time, can be to our advantage in tasting: we will not smell all the aromas of the product's bouquet in the first sniff, but with each sniff we will detect new and different aromas, thus gradually enriching the range of sensations that we can remember.
What if, on the other hand, we want to re smell an aroma that was perceived well at first and that we now involuntarily filter and can no longer smell? The only solution is to let your nose rest: breathe in fresh, odorless air and think of something else. In perfumery, smelling coffee is a practice used to reset the sense of smell because it is a very intense and different smell from those present in perfumes allowing one to "distract his nose".
And what can we do if the smell does not come back even after having rested the nose? This is the case when we smell a wine's bouquet in the glass. The habituation of the sense of smell is not the only factor that plays a part. In fact, it must be remembered that when in contact with the air, wine begins to evolve chemically: some aromas disappear quickly and others emerge with more intensity.
So? The best you can do is try and memorize the scents you smell right away the first time and if the tasting lasts a long time, remember to take a break to distract yourself and let your sense of smell rest.
And of course, TasterPlace aromas collections can also help you learn particular scents so you can recognize them right away!