Is This Rose Fragrant? Depends on the Nose of the Beholder!

By Jacques Ferare

In my most recent blogs, I discussed how to define fragrance in roses and how it can be transmitted to future generations, as well as how it can be described to create new perfumes. Here I will try to answer the very basic question of  what makes a particular rose fragrant (or not), and why some people will find a particular rose very fragrant while the next person will not find it fragrant at all. The answer is rarely a distinct yes or no. Numerous physiological and environmental factors are involved to make it a very subjective and personal answer. This may be a bit technical at times, so bear with me…

The fragrance of a rose changes as the flower evolves. In very tight buds, before opening, the molecules that create fragrance are not released yet. The fragrance will develop as the petals unfurl, until the bloom is fully open. This explains why most florist roses sold as fresh cut flowers do not have any fragrance. They are cut and separated from their source of food (the rose bush itself) before the fragrance develops. This separation also interrupts the biological processes responsible for the fabrication of the molecules creating the fragrance. Another explanation, more commonly known, is that rose breeders look primarily for longevity in creating new florist roses, and that long vase life usually means the roses will have very hard petals with less pores, thus less likely to have the capacity to release much fragrance.

The rose also follows an internal cycle that varies during the day. This cycle has been accurately measured and shows that the maximum release of fragrance occurs early in the afternoon, right after what plant physiologists call “The Noon Depression.” (Something we can all relate to, right?). Environmental factors also play a significant role, as it is well known that roses do not release a lot of fragrance during rainy or windy days. A calm atmosphere with high relative humidity and temperatures above 70 degrees are the best conditions for maximum expression of the fragrance. That is on the rose side.

On the human side, the sense of smell is unique to each individual, because an odor, good or bad, does not exist per se, but is the result of the encounter between a molecule and a receptor, in this case the neurons in the mucous membrane of our nose. So the characteristics of any fragrance depend on the person as much as on the compound itself. This process is highly subjective, both for the perception of the odor itself, which is unique to each individual, and for the appreciation of the smell, which usually results from learning and experience.

When the molecule comes in contact with the mucous membrane inside the nose, the neuron sends a signal to the part of the brain know as the olfactory bulb, where the signal is analyzed and processed.  If numerous receptors are activated, the odor will be perceived to be strong and the information will be transferred to the central memory for identification and storage. The human body packs about 10 millions olfactory nerve fibers in a little less than 1 square inch of our nasal mucous membrane.  That’s a lot of processing power! These specific neurons are in fact the only part of our nervous system directly in contact with the outside world. Each of these neurons is highly selective and responds only to a certain amount of stimulus by fragrance molecules. Practically, this means that each individual will perceive each compound differently, and that some people may not be sensitive to a given fragrance molecule. If a person is insensitive to a major component of the fragrance of the rose he or she smells, the rose will be perceived as non-fragrant, no matter how strong the fragrance is to other people. To illustrate this, you can try this experiment with a group of friends by asking them to judge the intensity and the quality of the fragrance of a given rose. You will be surprised by the result. Chances are, there will be as many variations in the evaluation as there are people in the group.

Human vocabulary is not as accurate with smell as it is with colors. To identify a given fragrance, perfume makers had to create a specific jargon that enables them to define accurately what they smell by specific words (see my last blog entry for more details).  The rest of us rely more on our memory to define a fragrance, by association of a particular smell with a given event, or situation, as well as a common word they associate with that odor.

There is some analogy in the way we perceive fragrance and how we listen to a choir. To fully appreciate the beauty of a choir, one needs to appreciate the whole group, while being able to identify each singer individually as the ear is attracted by his or her individual performance.  The pleasure comes from the whole experience as well as from being able to isolate a specific sound (or, in this case, fragrance).

However, in the end, whether it’s the perfume of a rose or Mozart’s Requiem, you don’t have to be an expert to enjoy it.

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