You can remember the way something did smell, but you can not recreate that smell no more then you can create a banana peel in your head by thinking about it's texture. Producing the smell itself from no discernable exterior source would require you to be able to control matter with your mind which not many people can do.
There is a physiological difference between the sense of smell and the other sensatory functions, like vision and so on. The "smell nerves" connect directly to the inner part of the brain, where the "primitive" functions reside. (Hunger, fear, satisfaction...)
All animals rely on the capability to avoid bad food and find good food, and smell is vital here. Hence the strong connection to the dissatisfaction functions. (Kimmelman,1990)
Vision, hearing, feel and so on connect to the outer parts of the brain, the cortex, where the "higher" functions reside (thinking, mind, fantasy). You use your cortex to imagine things, and it is reasonably easier to do so with processes that have their origin in the vicinity, with good, wideband connections.
Since you have more than enough to read on the sense of smell, I'll confine most of my comments to the sense of taste because you have confused taste and smell in your question. This is a common confusion. Properly speaking, taste and smell (or olfaction) are two different senses. Informally, people lump taste and olfaction together because most of the sensory stimulation we get from food comes from the aroma than from the taste. (Hoffman,1998)
Smell is a sensation caused by molecules coming in contact with the olfactory region in a remote part of your nose. Taste is a non-tactile sense perceived entirely within your mouth Sweet is not a smell. It is one of the four senses of taste, the others are sour, bitter, and salty. Each taste is associated with different sets of receptors on your tongue.....
