BY WILL LAPAZ, Essential Oil Specialist, for The Ananda Apothecary

MAY 17, 2016 - Updated: January 3, 2017

While a proper chemical analysis is necessary for objectively determining the purity, or lack thereof, of an essential oil, chemical analysis is not typically able to determine a high quality essential oil from a lower quality one. Once the purity, authenticity and the proper or accepted chemistry of an essential oil is validated, quality is often subjective and comes down to if you like the aroma or not. Liking the aroma, however, is typically not a good test of quality unless one is trained in olfactory evaluation and proper organoleptic evaluation techniques are followed. Determining aromatic quality and selecting an essential oil for purchase (based on evaluating several samples from different distillers or suppliers), once we know that the samples are genuine, should rely on a thorough organoleptic analysis - a combination of aroma (smell), texture (touch), color (sight), as well as taste. While taste is not always necessary, it can play an important part of an evaluation for certain essential oils. Color variation can likewise be a very important indicator of quality and is also used to detect an older or oxidized essential oil. In this way, we use our organs of perception to determine the good quality from the poor, with our sense of smell being the one most heavily relied upon.

One needs to learn how to smell an essential oil in order to evaluate its quality, as almost no one in our society has been trained to use their olfactory sense in this way, and the sense of smell tends to be the least important of the five organs of perception in our culture. To properly evaluate the aroma of an essential oil and especially in order to choose the best one from a selection of several different essential oils of the same species and distillation or extraction technique, one needs to put a small amount of the various essential oils on perfume test strips (scent strips). The same amount of each essential oil on every scent strip is important. The strips need to be labeled and dated and the time noted. The aromatic profiles of each scent strip then needs to be evaluated and notes taken directly after dipping the test strip and then at periodic intervals such as after 15 to 30 minutes, at 45 to 60 minutes, at 2 hours, 4 hours, 8 hours, the next day and onward for several days, especially for those essential oils that evaporate slowly and are often subjected to adulteration such as sandalwood, rose and jasmine. As the essential oils on the scent strips dry-down, the aroma will change and it is common that the high quality essential oils will display a variety of aromatic notes over the course of the evaluation, typically several days, but can last up to several weeks.

It is vitally important to not compare and evaluate essential oils directly from their bottles for the purpose of determining aromatic quality. If one smells the exact same essential oil from different size bottles or with a different quantity of the essential oil in the same size bottle, it is inevitable that the bottles of the same exact essential oil will smell different. One reason for this is that different amounts of molecules are reaching our olfactory sense receptors and changing the way our brain identifies the aromas. For a quick comparison of several essential oils in their bottles, it is better to smell the caps of the bottles, rather than the bottles themselves because this will tend to even out the amount of aromatic molecules reaching the olfactory sense receptors. However, for a proper evaluation, scent strips evaluated over time is the best and most reliable method.

The other critical thing one must learn is how to smell correctly and what to smell for. It is recommended that a person exhales most of the air from their lungs and then hold the scent strip under their nose. Then breathe in - in one long, slow inhale or alternatively, breathe in with successive short sniffs. It is best to use both methods for the same essential oil to uncover subtleties that might otherwise go undetected. It is also important to look for how the aroma changes during the inhalation. For instance, toward the latter part of a complete inhale there will be subtle changes in the aroma that often lead to an impression of the complexity of the essential oil. Another way to say this is that at the top of the inhalation, look to uncover hidden notes that are not immediately apparent.

A good quality essential oil should, in general, be more complex than a poor one. Take neroli essential oil for example. The average neroli essential oil will display its characteristic aroma that is rather high on the scale of base to top note. It may be very likable and even beautiful but compared to a really good neroli it won't have as much depth or complexity. The elusive, excellent neroli oil will be very complex and the aroma profile will include a surprisingly deep note, called an indole note, that is also found in jasmine and other floral absolutes. Although neroli does not smell like jasmine, it will display a similar deep or lower note that is a significant part of jasmine and also of a good neroli essential oil. So, in this example, the good neroli essential oil will display, in addition to its common floral notes - complexity, depth, roundedness, fullness, vibrancy and liveliness. With other essential oils this complexity can also be uncovered and should typically be there, in addition to the main notes being crystal clear, clean and pure with no off-notes.

Two other examples of essential oils that illustrate what to look for are wintergreen and rosewood. These two are often times lab-made, since they are relatively simple essential oils that consist of one constituent making up most of the essential oil; methyl salicylate in the case of wintergreen, and linalool in the case of rosewood. In these cases one can often determine through smell alone which ones in a group of samples is lab-made and which are authentic. The lab-made essential oils of these two types will display a consistent, clean, bright, and lovely aroma, while the true essential oils will be more complex aromatically. This is due to the small amount of natural constituents that will not be present in the lab-made oils. The true essential oils may not smell quite as clean, crisp and clear, however, they will have more depth, a fuller aroma profile. The various notes in the true essential oils of rosewood and wintergreen may be mistaken for off-notes to the uninitiated evaluator and these oils may further be rejected as poorer in their aroma, especially if the evaluator has been working with lab-made rosewood and wintergreen in the past. Whereas the connoisseur with many years of experience will chose the more rough and less refined wintergreen and rosewood oils as the ones that they want to purchase and blend into their formulas, since they understand that these additional aromatic notes are a part of the authentic essential oils.

Often when I evaluate essential oils aromatically in order to determine which one of several are the "best", I can simply start by finding those essential oils with off-notes - those aromatic notes that should not be there, whether they are offensive, sharp, chemical-like, or otherwise distract from the beauty of the true essential oil. I will reject these and the remaining essential oils will then be subject to a more in depth evaluation of the subtle aroma and specific notes over the course of at least one day and often for several days or even several weeks in certain cases. The most aromatically beautiful, complex, and well-rounded essential oils will be chosen as the best quality and they invariably will not have any undue sharpness, flatness, burnt, or other off-note. I also look for aliveness or brightness that for me translates into bioavailability because the more “alive” essential oil will have its spirit or subtle essence intact and it will be able to harmonize better with the living systems of the body, no matter the way in which it is used - through the breath, skin, or by careful ingestion as a flavoring or as a therapeutic agent. Old or otherwise poor essential oils (even though they may be genuine and authentic) display less aliveness and although they may still be appropriate for some applications, they will not be as compatible with the body, its cells, and its systems. The fresher, brighter, and more alive essential oils, however, are better able to harmonize with and support the body’s natural healing ability.

Another important factor to evaluate for, and the reason why the scent strips need to be kept for several days or longer, is the essential oil’s lasting power or sillage. Typically, while evaluating and comparing essential oils in order to determine which ones should be selected for inclusion in a company’s catalog of offerings, or for making products or for home use, one of the determining factors of good quality is its lasting power. This assumes, of course, that there are no off-notes because synthetic aroma-chemicals have a notorious tendency to last a long time - longer than their natural counterparts. This is another reason that multiple day or week long evaluations are necessary as the synthetic notes last longer than natural notes and will become more pronounced and easier to distinguish after several days. However, assuming we are starting with unadulterated essential oils, during the evaluation process we will notice that one or more of the samples last longer than the others. Often times the aromatically superior essential oils will also be the ones that last longer. While they are not always the longest lasting, they typically will not be among the short-lasting. If several aromatically “good” samples are similar in aroma and all their other qualities compare favorably, then the sillage comes into play and I will often consider that the longer lasting sample is superior to the one(s) that release their aroma and become “flat” more quickly.

The ability to determine essential oil quality is a learned process and applying oneself is necessary to learn this art in order to be good at determining aromatic quality, detecting off-notes and synthetics and be able to decide or recommend which essential oils should be purchased and which should be rejected. This article is only meant to be an introduction to the art of smelling plant essences and for evaluating the aromatic quality of essential oils (including absolutes, CO2 extracts, resinoids, organic extraits and enfleurage), and is not meant to be a complete study of the subject. There are more refined steps that need to be taken as you progress on the path of becoming an aromatherapist, essential oil expert, a natural perfumer, a distiller, a producer, a manufacture or purveyor in essential oils, or a “nose”.

It is important to note that there are many elements that come into play, beyond simply our sense of smell and following a few guidelines. Factors such as time of day, humidity and temperature are extremely important as these three factors can cause one to think that the essence is different that it is in reality. For instance, extremely low temperatures or humidity can cause one to believe that the essential oil being evaluated does not have a strong odor. However, if there is a change in these circumstances all of a sudden the same evaluator will remark on the strong aroma that the same essences is now emitting. Other important influences include what one has recently eaten and drank or if one has been smelling other aromatic items. Even the type of music or sounds one hears while in the process of aromatic evaluation becomes important - as any disturbance in any of the other sense organs will produce an effect on the olfactory system (or, at least, on how the brain interprets the aromas coming to it from the olfactory system). The other important consideration is personal - one’s natural aromatic ability, how long one has been actively smelling and evaluating essential oils, and the actual quality of those essences, as well as experience in evaluating aroma in different climatic conditions and working conditions all come into play. However, the above guidelines will help most everyone who works in the field of essential oils to become better at the art of smelling and determining quality and desirability when comparing and evaluating essential oils.