Qui delle divertite passioni
per miracolo tace la guerra,
qui tocca anche a noi poveri la nostra parte di ricchezza
ed è l’odore dei limoni
Eugenio Montale, I limoni
[…]Here, by some miracle, the war
of troubled passions calls a truce;
here we poor, too, receive our share of riches,
which is the fragrance of the lemons[…]
Eugenio Montale, The lemons (English translation of this poem found online).
Genova and The lemons
Take a map of the regions of Italy (or simply open an online mapping service…), and look northwest: a boomerang arches and embraces the stretch of sea in front of Corsica. This is Liguria and Genoa (Genova, in Italian), its historical and current capital, lies at the centre of this arc, like a keystone in a vault. Affluent port city in the Middle Ages and financial hub, Genoa coexisted with (but at times also fought against) Venice, the other ‘seafaring Republic’, vying for commercial predominance and for the control of trading routes in the Mediterranean. Yet, Genoa has arguably beaten its arch-rival by a naval mile in the contest of literature and music. For example, many think that the finest cantautore (singer-songwriter) of all Italian 20th-century musica d’autore (untranslatable, but literally ‘author’s music’: think of the Italian counterpart to French chanson) is a native of Genoa, Fabrizio de André. He has even been hailed as ‘the greatest Italian poet of the last hundred years’: although this is definitely far-fetched, he did bring about a sea change in the landscape of Italian music, by writing songs about themes previously neglected, or tacitly banned, in the love-centred and somewhat soppy lyrics of contemporary singer-songwriters.
Now leave Genoa behind you and choose where to turn, right or left: take a look at the western and eastern ends of Liguria, and you will see two of the most celebrated, most influential Italian writers of the 20th century. Prose and poetry face each other: Sanremo, in the western tip, almost bordering France, is the Riviera resort where the novelist, essayist and short story writer Italo Calvino (1923-1985) spent his childhood and youth years; opposite across the sea lie the Cinque Terre (lit. ‘Five Lands’), an area of outstanding natural beauty and World Heritage Site, which greatly inspired the earlier lyrics by Eugenio Montale, born in Genoa in 1896, arguably the greatest Italian poet of the last century. Liguria is the land where mountains choose to escape their earthly nature and dive into the sea, the great salty blue beyond the shore that features in so many of Montale’s first poems; Liguria is the land where the rugged coastline can become complex and intricate, almost like a fractal, like the combinatorial or structuralist schemes informing some of Italo Calvino’s works. Invisible cities is the title of one of them: short descriptions of these “invisible cities” are arranged according to a thematic structure that follows an iterative order throughout the book. The overarching frame story of Invisible cities is Marco Polo’s fictional conversation with Kublai Khan about these cities, something clearly inspired to the 13th-century travel accounts of the real Marco Polo, The Travels of Marco Polo. A theme of Invisible cities includes “cities & memory”, and if I were to write my own account of the cities of my life, I would definitely place Genoa in this group…My invisible Genoa looks like Zora, one of Calvino’s invisible cities:
“Cities & Memory 4
Beyond six rivers and three mountain ranges rises Zora, a city that no one, having seen it, can forget. But not because, like other memorable cities, it leaves an unusual image in your recollections. Zora has the quality of remaining in your memory point by point, in its succession of streets, of houses along the streets, of doors and windows in the houses, though nothing in them possesses a special beauty of rarity. Zora’s secret lies in the way your gaze runs over patterns following one another as in a musical score where not a note can be altered or displaced. The man who knows by heart of Zora is made, if he is unable to sleep at night, can imagine he is walking along the streets […] This city which cannot be expunged from the mind is like an armature, a honeycomb in whose cells each of us can place the things he wants to remember.[…] Between each idea and each point of the itinerary an affinity or a contrast can be established[…]”
(Italo Calvino, Invisible Cities, translated by William Weaver, Vintage Editions).
There are cities where we sense a resonance with their vibrations: we have never lived there, we do not even love them at first sight, and yet we strangely feel at home. There is usually no point in wondering why: it is just like a subliminal perception. So is Genoa for me, city and memory, and when I tread the stones of its twisted lanes I know that I am a stranger, a casual visitor to a city that maybe I do not even like; nevertheless, I feel at ease, moving effortlessly on those, in Montale’s words, frail “spiderwebs of the memory”, as if a vague reminiscence could still help me find my way. I navigate the visible city following the map of the invisible Genoa within me. On rainy days, gray skies loom large above the Ligurian Sea and you know that they are there to stay: the infamous ‘Genoa low‘ clashes against the mountains, squeezing rain onto the city from its spongy clouds. This is when I would think about Montale’s poem I limoni as I am wandering aimlessly, victim of a literary Wanderlust:
La pioggia stanca la terra, di poi; s’affolta
il tedio dell’inverno sulle case,
la luce si fa avara – amara l’anima.
The rain exhausts the earth then;
winter’s tedium weighs the houses down,
the light turns miserly-the soul bitter.
Then, as I picture myself following in Montale’s footsteps, like a Parisian flâneur in search of a flashing idea, I, too, yearn for that sudden surprise, the golden light of ripe lemons appearing all of a sudden after you turn into a narrow alleyway, the plump fruits hanging heavily from a lemon tree grown in a pot, standing in a courtyard.
Quando un giorno da un malchiuso portone
tra gli alberi di una corte
ci si mostrano i gialli dei limoni;
e il gelo del cuore si sfa,
e in petto ci scrosciano
le loro canzoni
le trombe d’oro della solarità.
Till one day through a half-shut gate
in a courtyard, there among the trees,
we can see the yellow of the lemons;
and the chill in the heart
melts, and deep in us
the golden horns of sunlight
pelt their songs.
A gate left ajar lets us catch a glimpse of the lemons, we would like to go and touch and smell the zesty fragrance of the rind. Yet, the concierge of the mansion spots us and rushes to locks us out. There we stand alone, in the torrential winter rain.
Chemistry and the invisible lemon.
Oxford is a very visible city, but lemons are rarely to be found. This is in stark contrast with Liguria, a land where citrus fruits have always flourished in the mild climate of the region, thanks to the protective embrace of the mountains. Some online sources report the whopping figure of 20-25 million lemons produced in the sole city of Sanremo in 1662. At the same time, somewhere north of the Alps, lemon trees started to be grown, too, requiring orangeries, glasshouses and conservatories: the renowned Botanic Garden of the University of Oxford still houses a couple of citrus plants in its conservatory, where they have been lovingly kept warm ‘since the 1600s’, as its website proudly states.
Anyway, it it time for chemistry and the kitchen. Once upon a night I found myself at a friend’s place, ready to do one of my favourite things: improvisation (aka “messing up”) in the kitchen, something I seldom allow myself to do because of the imprinting of my laboratory training. A jar of ready-to-use chickpeas peeping from a shelf was too strong a temptation for us to resist: let’s make some hummus! By the way, one could try and unify the entire Mediterranean world1 (and beyond) under the name of the blessed chickpea. We set sail from the western Andalusian coasts, where espinacas con garbanzos (spinach and chickpeas) are a staple dish, we lay at anchor for a stopover at any port of the Ligurian Sea, where the whole Riviera from Nice to Pisa feasts on flatbread made from chickpea flour (known as farinata in Liguria and socca in the Nice area), and, following the ancient sailing routes, we finally reach the shore somewhere in the eastern Mediterranean, for example the port of Acre, where ships from Genoa would once dock, load cargo, and trade, and where hummus will now keep our hunger pangs at bay.
The soft chickpeas easily yielded to the blade of the blender. Then I added some sesame paste, or tahini, and went on mashing the delicious mixture, tasting it on the go. Looking scrumptious. At this point, I turned to my friend and asked her: “Could you pass me a lemon or some juice please?”. Panic. The air stood still, those silent seconds where people cross their gazes without saying a word, knowing all too well what comes next. “I’ve got no lemon juice, I’ve got no lemons”, said she. Then she pointed to a small, bright green lime: “Use that instead!”, she suggested. I could have, maybe I should have, taken the lime and squeezed it, but I could not help grasping this opportunity for some unexpected “messing up” in the kitchen. I felt like frolicking and so I turned down the offer of the alternative citrus fruit and started thinking: “OK, let’s say that the little lemon juice added to the hummus is just there to correct the flavour: I don’t expect the texture of the hummus to depend a lot on the change in pH…the texture’s more a matter of balance between thick tahini and chickpea water”. In a sense, now I think that I was following the path traced by Italo Calvino in his quote above: “Between each idea and each point of the itinerary an affinity or a contrast can be established“.
Acidity: that is what lemon juice is (almost) all about. The holy book of all food lovers2 shows that the juice is 5 % in acids (as weight/weight percentage). The main sour character is citric acid, an interesting compound that ought to deserve much more than this brief mention in a blog post about hummus. For the moment, let us just remind that it is an allowed food additive, under the EU code E 330. Malic acid comes in a far second in the acid ranking, well below 0.5% 3 . Biochemistry lovers will remember that both citric and malic acid feature in the Krebs cycle, or citric acid cycle.
Then there is a sweet note to the flavour of lemon juice, which arises from the juice sugars, having a total weight content of 3.16 %, slightly lower than that of the acids.
However, as we all know, lemon is much more than its juice: the rind of the golden fruits has a pleasant, smell, arising from some fragrant molecules: limonene and citral in the first place. If we take a look at the molecular structure, we understand the significant difference between the reactivity of these two compounds.
Limonene is a sturdy molecule that belongs to the family of terpenes. You can mistreat it to a certain extent, and it will still be fine. It is a hydrocarbon, there is not much one can do to it unless one targets the double bonds. What I have drawn here is the stereoisomer found in lemon (question for those chemists who loved organic nomenclature as undergrads: is it R or S ?).
Citral, instead, seems poised to shortcut and curl into a comfortable 6-membered ring, with a little help from some acid, and all it takes for citral to become an aromatic molecule is some oxidiser. And beware: citral is actually a mixture of two isomers, neral and geranial, having a different smell.
Too bad citral falls apart in harsh conditions: a lemon-scented bleach or household detergent is the hallmark of cleanliness; if only citral were not so delicate! The quest for a substitute that could be stable in acidic and/or oxidising conditions has almost acquired a legendary status in the perfumery literature. It is cited for example in The Secret of Scent by Luca Turin, a must-read for perfume lovers, and maybe the focus of a future blog post.
Back to the kitchen, how could we introduce some acidity and some lemon-like flavours in the hummus-to-be? Spicing it up with the right ingredients, that was the way to go, but what to add? Fortunately, the kitchen larder was open and lots of spices were beckoning me over: I would quickly find what I needed.
First I sprinkled the hummus with a dark-red powder having a distinctive, tart note: there was sumac, hailing from the same part of the world as hummus itself, and the combination of the two is a match made in heaven. Sumac is a very peculiar spice in that it imparts acidity thanks to its high content in…yes, here we go, malic acid. Moreover, sumac came in with an additional bonus: it also contains some limonene.
Then I opened a small bag full of a brownish powder, and I savoured the fresh smell of ground coriander, its citral notes chiming with the taste I was trying to compose. I sprinkled the hummus with some coriander, I mixed, then I added a bit of olive oil and served. In the end, the lemon-free hummus was given the thumbs up by my friend.
But can one really assemble a lemon from, er… ‘first principles’, bottom-up? Do chemistry and cooking, which are both essentially combinatorial in nature, really have something in common?4
The curse of the alchemist
Regardless of the answer to those questions, what matters here is the idea of artefact contrasted to natural. Oh, here’s another Pandora box popping open…I promise that I will keep it short and simple (look elsewhere5 for the small print), while trying to be careful as I cross this minefield.
In a nutshell, (al)chemists have often been accused of concoct counterfeits, bogus surrogates of the real stuff, their ‘crime’ straddling plain quackery and outright fraud. From the arguments of Scholastic philosophers to today’s alleged supremacy of the natural (whatever it means) over the artificial or the chemical, the perceived image of (al)chemists seems to follows, at least ostensibly, a unique thread throughout the centuries. Dante Alighieri, in his Divine Comedy, places alchemists deep down in hell, in the Eighth Circle along with fraudsters, and more specifically in the same bolgia (a hole in the ground) as falsifiers. For the 10th-century philosopher Avicenna, alchemy is a form of deception, while the great Thomas Aquinas dismissed alchemy simply as an anomaly outside nature (‘praeternatural’). Today, the label ‘natural’ is often misused as a tacit antonym of ‘chemical’, leading to all sorts of paradoxes, chemistry as a scientific discipline being caught in the crossfire.
Yet, is the rift between the natural and the artificial still so deep? After all, the fear of some chemicals could easily coexist with an appreciation of others5, perceived as a boon to the society’s well-being. Indeed, the 2015 survey Public attitudes to chemistry in the UK by the Royal Society of Chemistry shows that people are quite pragmatic about chemicals, to say the least. Figures show that 60% of the public agree that “everything is made of chemicals” and 70% are in agreement with the statement “everything including water and oxygen can be toxic at a certain dose”. Paracelsus is alive and well, and we chemists should really take the time to sit down and reflect on our own preconceptions about the chemophobic public.
Calvino prematurely died 30 years ago. His legacy to Italian literature and culture is still under debate: some critics find that Calvino’s style and poetics have provided the following generations of writers with an invaluable framework; others, however, believe that his influence has ended up looming large on Italian literature, more as a magnificent hurdle to overcome than as a reference point.
At that time of his death, the writer was working on a series of lectures on literature to be delivered at Harvard. Fortunately, his notes were edited and collected in a book available in English translation, Six memos for the next millennium. Six seminars, each on a ‘value’ (and its opposite) that Calvino considered worthy of attention with an eye to 21st-century literature. Six memos for the next millennium and Invisible cities are similar in that they single out beacons, vital reference points helping us to navigate, respectively, the vast universe of literature or the everyday chaos that surrounds us. But like any map, we are free to choose if to trust and follow them or not.
At this stage, however, I would like to remember another book, The Castle of Crossed Destinies, in which Calvino crafts short stories by interpreting tarot cards randomly placed on the table. In this novel, mute characters who meet by chance in a castle or at an inn try to tell their own stories by picking, laying and arranging tarot cards; an onlooker, standing in for the writer, watches and tries to work out what the other characters try to narrate. From this point of view, The Castle of Crossed Destinies also draws on those great works of 14th century literature, Decameron by Boccaccio and The Canterbury Tales by Chaucher, which feature a group of characters taking turns at telling stories -and turns are part and parcel of all card games.
Anyway, in one of these tales, Calvino sees the trump card of The Magician (aka The Juggler, or Le Bateleur in the French original) as a proxy for the (somewhat stereotypical) alchemist, who tells how he sold his soul to the devil. Sounds familiar?
[…]our companion was, in fact, one of those scholars who scrutinize alembics and crucibles[…]trying to wrest from Nature her secrets, and especially that of the transformation of metals[…] from his earliest youth […]he had no other passion […] save the manipulation of the elements, and for years he had waited to see the yellow king of the mineral world precipitated in the depths of his cauldron.[…] This event must have been indicated in the following card, which was the enigmatic First Arcanum, sometimes known as The Juggler, in which some see a charlatan or magician performing his tricks […].
(The tale of the alchemist, pp. 16-17)6
The second tale talking about alchemists is a much more intriguing piece, in my view: the alchemist is compared and contrasted to the figure of the knight-errant, and both of them come in with an alter ego, Doctor Faust (who else?) for the alchemist, and Perceval for the knight-errant. Put it in chemical terms, I see two resonance structures of the same molecule: the alchemist who “must (instead) free himself of all egoism […] to achieve transformations of matter“, who “tries to make his soul become as unchangeable and pure as gold” and Doctor Faust, “who inverts the alchemist’s rules, makes the soul an object of exchange” (Two tales of seeking and losing, pp. 90-91).
So, what kind of (al)chemist do you think you are?
Only now that I look back do I realise that this post has gone a long way, from Liguria through hummus to Calvino and eventually the Faustian ambitions of his alchemist. It is as if I were trying, as Marco Polo did in his travel accounts to Kublai Khan in Invisible Cities, to give an overview of the entire known world by piecing together his memories. Had he met the Faust of The Castle of Crossed Destinies, he would have agreed with him:
“There is not an all, given all at once: there is a finite number of elements whose combinations are multiplied to billions of billions, and only a few of these find a form and a meaning and make their presence felt amid a meaningless, shapeless dust cloud; like the seventy-eight cards of the tarot deck in whose juxtapositions sequences of stories appear and are then immediately undone” (Two tales of seeking and losing, p. 97).
Faust, this time I have got an ace up my sleeve, too.
Such stuff, that all is made on.
1. Neighbours are often too similar to love each other. So, there was a time when Pisa and Genoa, too, were at war. Memories of ferocious naval battles and bloodshed are still alive in the two cities. The same goes with the ongoing Israeli-Palestinian conflict. A humble suggestion: the chickpea could be the seed of durable peace… When I first wrote this footnote I was kind of joking, now I have found out that someone in Isreal has already done so: “Hummus joint gives Jewish-Arab tables 50% off“. As the newspaper writes with a witty humor, that’s chickpeace.
2. On Food & Cooking, Harold McGee, Hodder & Stoughton, 2004
3. Liu, Y., et al., History, Global Distribution, and Nutritional Importance of Citrus Fruits, in Comprehensive Reviews in Food Science and Food Safety, 2012, 11, 530–545. doi: 10.1111/j.1541-4337.2012.00201.x
4. According to a Lebanese cook who took part in a food programme on the French radio, On va déguster, replacing lemon with sumac in hummus is tantamount to blasphemy. If you speak French, you can listen to the programme, focussed on Middle Eastern cuisine from Aleppo to Tel Aviv through Lebanon.
5.Chemistry: The Impure Science, Bernadette Bensaude-Vincent and Jonathan Simon, Imperial College Press, 2012 (2nd edition).
6. All quotes from The Castle of Crossed Destinies, translated from the Italian by William Weaver, Secker & Warburg (London), 1976