This article is by Robert Calkin, originally published in The Royal National Rose Society Historic Rose Journal Autumn 2013. If you are not a member of the Historic Rose Group, articles such as these are just one reason to join! All the photography is mine.
The weather this afternoon is so foul, I’ve enjoyed the excuse and opportunity to transcribe the article and choose a few photographs from my ‘back catalogue’ to brighten my day.
The description of fragrance is fraught with difficulty. To begin with there is no definitive vocabulary of smell in common use, as there is for example for colour; we can only describe a fragrance by association. But this in itself raises a problem in that people have both different perceptions of small and different associations based on past experience. In trying to describe the fragrance of a rose the problem is often compounded by its underlying complexity.
The sense of smell is the most primitive of our senses Unlike that of vision or hearing, it is a chemical sense, which brings with it the ability to recognise and respond to chemical substances in the environment. Some of our odour preference, such as for the smell of flowers and fruit, are probably innate. Others we learn by association. This ability for recognition and association can last us a lifetime and it is a common experience for a smell to bring back memories of childhood, the smell of a room or of a cupboard, or even of a favourite grandmother.
The composition of rose fragrance is often exceedingly complicated. Analysis of the oil, the attar of rose used in perfumery, distilled from the Damask rose ‘Kazanlik’ shows it to be made up of more than 450 chemical components. Some of these we would recognise as smelling of rose. Others, the majority, are actually quite unpleasant and some intensely strong. But they come together to give a unified fragrance which we can recognise and learn to associate with a particular variety of rose. The most beautiful fragrances found among roses, for me at any rate, are those which have this apparent singleness of fragrance, a unique personality, based on a perfectly blended complexity. This is particularly noticeable in species roses and many of the early hybrids such as the Damasks, Albas, Portlands and some of the Bourbons. Further interbreeding has in many cases led to rather more muddled fragrances – blends that are less appealing.
But even within the fragrance of a finely scented rose it may still be possible to pick out other associations such as lemon, blackcurrant, raspberry, honey, narcissus or violet, and most of our attempts to describe the fragrance of a rose are based on such comparisons. But, as already noted, we all have different associations. We also have different thresholds at which certain smells become apparent. To one person, a rose may smell of grapefruit, to another of blackcurrant and to another of cats. They are in fact all correct since the chemistry of these different smells is closely related. This particular mix of character is found in the famous ‘Mme Alfred Carriere’, being particularly noticeable late in the season, but all within the general designation of a rose. Many quite heated discussions can arise when discussing the description of a fragrance.
To add to the difficulties, as when trying to write a fragrance description for a rose, many, especially among the more modern hybrids, can change their fragrance depending on the time of day, maturity of the flower, the season, or the prevailing weather conditions. Even two flowers on the same plant can sometimes smell quite different. Sometimes they may smell closer to one parent, sometimes to another. Different chemical pathways get switched on under different conditions.
Apart from the more obvious associations, much of our fascination with the smell of roses comes from recognition of the different underlying types derived from the ancestral rose species and their early hybridisation. It is now the general practice to classify rose fragrance into such categories as Old Rose, Musk, Fruity, and Tea, and these can be broken down into further subdivisions. Of these, that of the Old Rose fragrance, associated with the old European roses descended from Rosa Gallica, is what is generally recognised as the quintessential rose fragrance. There are simply no other words to describe it: it is just simply ‘rose’. The word has become of the reference points of fragrance description such as lemon, violet, vanilla, and cinnamon.
This fragrance is based on the presence, in various proportions, of four main chemicals: citronellol, geraniol, nerol and phenylethyl alcohol. The first three are closely related alcohols and typically rosy in character, ranging from the warmth of citronellol, to the more brilliant character of geraniol and the harshness of nerol. Language is always quite inadequate to express the difference. Related to them is the chemical citral, which is one of the main components of the smell of lemons and often found as a component of rose fragrance, sometimes becoming dominant. Phenylethyl alcohol is perhaps the most recognisable of the four alcohols, being typical of rosewater and Turkish Delight. The fragrance of the Portland rose ‘Comte de Chambord’ is an outstanding example of the Old Rose fragrance based on these four materials. Citronellol (not to be confused with the smell of citronella) and geraniol are also components of the smell of geranium, a character found in ‘Stanwell Perpetual’.
Here I am deliberately moving into a more definitive language of fragrance, that of a perfumery chemist. Perfumers are trained to recognise hundreds of chemicals by their fragrance and to analyse by nose the compositions of complex mixtures. This analysis can now be confirmed by the use of gas chromatography. By identifying many of the major components of a rose fragrance the trained ‘nose’ can accurately place a rose within a classification related to its parentage. The perfumer is also in the privileged position of being able to describe quite accurately the smell of a rose to another perfumer. But with a little practice, some of this ability can be acquired by anyone with an interest in rose fragrance.
As in learning about wines, comparison is everything. Smelling two roses against each other and trying to describe the difference, however inappropriate the words, is the quickest way of learning to recognise the different types of scent. Once the recognition of the major categories has been established, new variations can be stored within the memory.
The introduction of roses from China at the end of the 18th century saw a dramatic development in the fragrance of roses. Many of these roses were hybrids of ancient origin and are remarkable for the variety of fragrance found within the group. But one rose in particular, the famous ‘Old Blush’, when crossed with the old European roses, was to have a profound effect. The fragrance of a rose can be thought of as reflecting the general biochemistry of the plant, dictated by the presence of certain enzymes capable of producing the many types of material that make up the fragrance. When two species are brought together the resultant fragrance is not just a mixture of the two but of the underlying chemistry. New chemical pathways are introduced producing materials not necessarily found in either parent.
Although ‘Old Blush’, when it produces it, has a fragrance reminiscent of sweet pea, it also has the ability to produce an entirely fruity character when crossed with the old European roses. This is achieved within the chemistry of the hybrid by converting particular alcohols, in particular phenylethyl alcohol, into their equivalent acetates, which as a group are fruity in character. This is particularly noticeable in the early Bourbon roses such as ‘Souvenir de la Malmaison’.
Hybridisation has lead to the introduction of many new variations into the repertoire of fragrances produced by roses. Many of these defy description. A recent development has been the accentuation of a smell reminiscent of one that is common to orange blossom, jasmine, and lily of the valley – three of the floral fragrances most widely used in perfumery. To some people, it is more reminiscent of honeysuckle. This is a smell related to a chemical known as indole. At low concentrations this is perceived as being warm, floral and somewhat erotic in character. At higher levels it is perceived as unpleasantly animalistic with faecal associations Different people have different levels of sensitivity to the smell so that its appeal can vary enormously among different groups of people. Women tend to like it more than men.
An interest in their fragrance has led rose-growers in the last to identify certain groups of roses by their fragrance; for example the Musk rose, Hybrid Musks, Tea roses and Myrrh-Scented roses. Although the first of these, the musk-scented roses have been so-called since the Middle Ages, the name is in fact a misnomer. They do not smell of the genuine musk, which comes from the scent gland of the musk deer and which has been highly prized as an ingredient of perfumes since antiquity. However, two types of fragrances, both of which come from the stamens rather than the petals, carry this description.
The most widely found and the one which occurs in the ‘Musk Rose’, Rosa moschata, has an intense and very recognisable smell of clove; the chemical responsible, eugenol, being the same in both cases. The other is the fragrance found in Rosa arvensis, thought to be the musk rose of Shakespeare. This is an intensely pungent smell, based on the presence of a type of chemical known as an aldehyde, also widely used in perfumery. However, what these fragrances have in common with real musk is their amazing power of diffusion, which is capable of floating the scent of the flowers for many yards across the garden. This may have been the association in so describing the scent in roses. Genuine musk was used in perfumery for just the same reason.
Another possibility is that the clove smell may have been described as musk as a result of the practice of merchants in the Middle Ages of adulterating the precious natural material with the less expensive powdered clove. The founding member of the wonderful group of Hybrid Musks, ‘Trier’, has an exceptionally powerful aldehydic musk fragrance. Nearly all the roses belonging to this group have inherited fragrances which are exceptionally diffusive.
When roses were first introduced from China, many of them had a fragrance quite unlike any of the more familiar European roses. For some rose growers there was a strong association between this fragrance and the smell of tea – and the name stuck. As early as 1820 there were clear descriptions of these roses as being ‘tea scented’. For many people, however, the association is not apparent and they prefer to think of the name as being linked to the tea clippers on which the roses were brought to Europe. But if you smell ‘Lady Hillingdon’, it really does smell of a freshly opened packet of China tea. The chemical makeup of the fragrance is totally different to that of the old European roses. Many of the ingredients were subsequently introduced into the Hybrid Teas where they mix, not always happily, with those of the old rose fragrance.
Describing roses as having the myrrh fragrance can also be misleading, since what first comes to mind is probably the smell of myrrh, a resinous substance associated in scripture with gold and frankincense. In fact the name is derived from the wild herb Sweet Cicily, Myrrhis odorata, which used to be called ‘myrrh’ and was common in the area where the fragrance was first associated with the Ayrshire Roses. To many people though not to everyone, this fragrance has a strong association with that of anise. Others describe it as liquorice or Pernod. To some it has less pleasant associations with household cleaners or the medicine cabinet. Chemical analysis of the fragrance does however confirm it to be closely related to that of anise, the main ingredient responsible for the fragrance, 4-vinyl anisole, which has an intense anisic character. The smell is highly polarising – you either love it or you loathe it. The preference seems to be partly gender specific, the smell being more popular with me than with women.
Just as hybridisation in roses can introduce new chemicals not found in either parent, so too can it result in an elimination of fragrance materials by shutting down of the chemical pathways leading to their synthesis. Within the complicated law of genetics, two differently but well scented roses with different sets of fragrance-linked genes can produce offspring with little or no fragrance. Many of the most important constituents of rose fragrance are derived from a group of chemicals known as terpenes. These occur widely in plants and are of little olfactory interest either to us or to pollinating insects. They generally smell of stems and leaves and what is sometimes described as the smell of florist shops or greenhouses. In many modern hybrids the typical fragrance associated with roses seems to have been lost in this way by the residual smell of terpenes. However, terpenes themselves can be reworked in different ways and the smell of cedarwood which can be identified in some modern roses is possibly of terpegnic origin.
The sense of smell is highly individual. We all have different association and sensitivities. Roses too, are highly individual and their fragrances often complex and mysterious. Although we may learn to love and to recognise their different perfumes it is perhaps part of their magic that mere words are often quite inadequate to express the variety and beauty of their fragrance. Article by Robert Calkin in the Historic Roses Journal Autumn 2013.
About the author – after leaving Cambridge, Robert Calkin embarked on a long and successful career as a ‘nose’ for parfumiers. Since retirement, he has used his expertise to help David Austin in connection with the scent of roses, and, in particular, to assist with the correct description of their individual fragrances.