The scent of roses in winter

Now winter is in its depths one great pleasure when viewing the barren landscape around is conjuring in the mind the scents of summer roses.

A little science

Rose scent is manufactured in the floral parts (petals usually, sometimes stamens) and released from specialised epidermal cells. The scent compounds (the so-called rose oils) are aromatic chemicals such as the rose monoterpenoids (e.g. geraniol) and rose ketones (e.g. damascenone). However there are very large numbers of chemicals that go to making rose scent, which accounts for the complexity and depth of the scent. In different roses these scents occur in differing proportions so giving the great variety of scents to be found in diverse rose varieties.

There are three major types of rose scent:

1. the classic Rosa gallica scent. In this the most abundant component is usually geraniol, as in the scented geranium (Pelargonium graveolens), and other deliciously fruity aromatic compounds;
2. the musk rose scent, a heavier scent of carotenoid-derived compounds
3. the tea rose scent, restricted to the china roses and their descendants. An important component of this tea scent is orcinol dimethyl ester [also known as 3,5-dimethoxytoluene]. Recent studies have shown that this is made by two enzymes, unique to tea roses, which methylate orcinol, first to orcinol monomethyl ester and then to orcinol dimethyl ester. The acquisition of these enzymes was therefore a crucial step in the evolution of the china roses.

The great rosarian G.S. Thomas wrote about roses with distinctive scents. Among these he mentions:

• Rosa bracteata - lemon
• Polyantha grandiflora - orange
• Adam Messerich - raspberry
• Vanity - sweet pea
• Ayrshire Splendens, Constance Spry - myrrh
• Fritz Nobis - cloves
• Lavender Lassie - lilac

These could all be due to a single dominant chemical. Orange and lemon scents are both due to the chemical limonene (different forms of the same chemical give orange or lemon). A raspberry scent might indicate the presence of raspberry ketone (hydroxyphenyl butanone). Sweet pea fragrance is due to the abundant production of linalool by sweet peas, the "rose myrrh" fragrance is said to be due to vinyl anisole, clove scent to eugenol, while a lilac scent might indicate the presence of the lilac aldehydes.

A rich and fragrant field of study!