Why does nature like the taste of lemons so much? There is lemon-scented thyme, lemongrass and, of course, lemons. I can鈥檛 think of any other commonly occurring flavour. Is it the same flavour, or do we just have a very broad definition of 鈥渓emon-flavoured鈥�?
鈥� Your correspondent is probably right that we have a broad definition of 鈥渓emon-flavoured鈥�; for instance, the characteristic sourness of lemons is caused by citric acid, but the other plants mentioned don鈥檛 contain this substance. It is more the smell or 鈥渆ssence鈥� of lemon that nature loves. I can add quite a few plants to the list, including lemon balm, lemon myrtle, lemon tea-tree, lemon verbena, lemon eucalyptus and lemon mint.
Chemically, the flavour similarities arise largely thanks to a fragrant compound called citral that is prominent in all lemony plants. Citral is a mixture of chemicals called terpenoids. Two other important bearers of lemon flavour, which appear in varying concentrations in the species listed above, include limonene and citronellal.
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So why is lemon such a popular flavour? We can approach this in terms of natural selection, by which complex mechanisms arise gradually when random genetic mutations are accumulated and passed on. Lemony plants are found all around the world and most are only distantly related. But then again, the synthesis of citral is well-established in plants and may date back millions of years. The process might even be simple enough to have developed independently in different plants.
After an initial lucky accident generated floral citral 鈥� a cosmic ray striking and altering a gene, perhaps 鈥� it may have acted as a lure for pollinators or a repellent to animals, both of which would have ensured the mutation鈥檚 natural selection.
For humans, lemoniness is distinctly attractive rather than repulsive. We are somewhat obsessed with the flavour, employing it extensively in beauty products, cleaning agents and, of course, food.
鈥淔or humans, lemoniness is distinctly attractive rather than repulsive and we use it extensively鈥�
The only other commonly occurring flavour I can think of is anise, an essence of aniseed, fennel, liquorice, star anise and even a type of mushroom. However, anise doesn鈥檛 come close to the prevalence of lemon.
Sam Buckton, Chipperfield, Hertfordshire, UK