“[…] La Cuisine moderne est une espece de Chymie. La science du Cuisinier consiste aujourd’hui à décomposer, à faire digérer & à quintessencier des viandes, à tirer des sucs nourrissans & pourtant legers, à les mêler & les confondre ensemble, de façon que rien ne domine et que tout se fasse sentir; enfin à leur donner cette union que les Peintres donnent aux couleurs, & à les rendre si homogenes, que de leurs differentes saveurs il ne résulte qu’un goût fin & piquant, & si je l’ose dire, une harmonie de tous les goûts réunis ensemble […]”
“Modern Cuisine is a sort of Chemistry. Today, the Cook’s science consists of decomposing, digesting and refining meat, of drawing nutritious and yet light juices, mixing and combining them together so that nothing could predominate and that everything could be tasted; finally, this science also brings these ingredients together in the same way as Painters do with colours, making them so homogeneous that the different flavours will turn into a fine, attractive ensemble, and, if I dare say it, a whole harmony of all flavours blended together”
Les Dons de Comus, ou les Délices de la table, François Marin, 1739, pages XX-XXI (the original ortography has been retained in the quoted passage).
“It could be your next blog post”, said P., a colleague of mine, “you could write about the stages of sugar syrup”. Vaste programme1, I would say during a bout of Francophilia…
Now, I’m definitely ready to take up my colleague’s challenge, but an entire blog post on syrup stages could simply taste too sweet for readers to eat. Besides, I know myself all too well: like a frantic honeybee, I will invariably end up flying from flower to flower collecting all nectar that I fancy: dwelling on a single subject does not really suit me, honestly.
That said, let’s start our sticky journey: get ready to wade through thick syrupy swamps and experience some of the hottest environments on Earth -or, maybe, just in the kitchen. What a timely moment to start exploring the universe of confectionery: the festive season is well behind us and some sweet thoughts will help to see us through the late-winter blues.
Spinning threads of words and sugar
When I first met the English confectionery, two similar Italian words came to my mind: a carefully-made wrapping or packaging (confezione) and the candied almond known as confetto. If one looks at etymologies, confectionery and its Italian soundalikes do share a common origin. Confetto, for example, stems from the Latin confectu, the past participle of conficere, meaning ‘to make, to prepare, to consume’, exactly like to confect, confection, and confectionery. Indeed, confezione as confectionery is attested in the Italian language, though with an archaic flavour, and both languages seem to use the very same word to indicate both a type of sweet and a medicinal preparation, usually coated in sugar. The latter was somewhat predominant in the Middle Ages, when table sugar was virtually only used in medicine, and this sweet powder from faraway lands would be stocked alongside expensive spices at the apothecary’s2. And, incidentally, early chemistry did take on board time-honoured pharmaceutical lore and ‘laboratory practices’3. (However this does not justify the confusing British use of chemist for shop, or person, where medicinal drugs are sold. This is something that the Royal Society of Chemistry itself has stressed in its report on the 2015 survey on public attitudes to chemistry).
Cracking the candy
Back to confectionery, this is a veritable galaxy in its own terms within the universe of food and cooking. When trying to make sense of the mind-blowing variety of confectioneries, a chemical mindset comes in extremely handy. That’s because, as philosophers remind us3,4, chemistry is a hybrid science with a good dose of taxonomy in it: like it or not, chemists have always had to deal with – and classify-the multifarious nature of the material world. Classification, however, is not important only for its own sake: the act of arranging chemical entities can beget chemical laws, as exemplified by periodicity. So, while we navigate confectionery, how can we come up with a taxonomy or an ordering principle of sorts? It would be great to explore the kitchen with the same scope and vision of Linnaeus, but that’s not what blog posts are meant to be (and mine are already quite lengthy). More simply, let’s break down the components of a confectionery product:
-additional structural ingredients (‘scaffolds’)
-tasty bits (‘inclusions’)
A candy, like many other edible things, is similar to a building. Sugars, and the way the cook handles them by controlling the temperature they reach during cooking, turn into crumbly wattle, solid bricks, or hard stones. Additional ingredients (if any) can help make sure that the building will have the texture that the cook and the eater desire, playing the role of concrete, mortar, daub, steel rods…Finally, add extras to taste, much as one would paint, decorate or plaster a wall.
So, when it comes to classifying candies, it is useful in the first place to address each of these three components in a sequential way, along with other specs of the recipe:
-relative proportion of sugars
-when and how the syrup is mixed to the scaffolds
-when and how inclusions are added
Beside these two triplets, the cooling of the reaction mixture is often even more important than all preceding steps, determining to a large extent the success or the failure of the synthesis, er, the recipe. This is where chemistry comes into its own: a cooling candy-to-be is undergoing crystallisation, a fascinating chemical process and a tricky practical operation at the same time.
Swirl down, sweet snow
How many times, when trudging through the white icing on winter’s cake, have you thought: ‘it’s crunching like sugar beneath my feet’? And, caught in a flurry of swirling snow, have you ever likened it to a sprinkle of powdered sugar?
If so, you’re a poet.
From the opening lines of La primavera hitleriana (‘The Hitler Spring’) by Italian poet Eugenio Montale…
Folta la nuvola bianca delle falene impazzite
turbina intorno agli scialbi fanali e sulle spallette,
stende a terra una coltre su cui scricchia
come su zucchero il piede[…]
The thick white cloud of crazy moths is whirling
around the pale lights and the parapets
spreading a blanket on the earth that snaps
like sugar underfoot[…]5
Poetry aside, thinking about snow is a useful starting point to get to grips with sugar crystallisation. Three general facts will come in handy later:
- When it’s too warm, it never snows but it pours.
- When it’s cold enough, it all begins with a seed.
- Wet, fine, frozen, heavy: many words to say snow.
Now, of course, do bear in mind that snow is an example of change of state of matter, while sugar crystallisation involves a solute (sugar) in a solvent (water) that clusters into precipitating (falling) crystals (solids). Both these phenomena, however, show common features.
A dance in three movements
With the help of my favourite food bible6, let’s take on sweet crystals. Looking back at the bullet list written above:
1 ) Let’s start from room temperature. When a big lump of sugar is added to water, (which is the first step of both recipes I will be talking about below), only some of it dissolves. That’s because room temperature is a slow microscopic waltz, and only when we crank up the cooker does the tempo change and quicken: water will then lead more and more sugar into a reeling dance, and the solid is dragged in this invisible, warming whirlpool.
Eventually, this solution will start boiling, not at the same temperature of sugar-free water, but higher, because of the dissolved sugar. How come? Well, think about this: sugar and water love each other. A lot. They make perfect dancing partners, but theirs is also one of those all-consuming, mutually absorbing passions. It takes brute force to separate water from its sweet companion, more than it would be required to separate water from water. Yet, heat is a ruthlessly efficient kidnapper, and more and more water is eventually lost into the air. So, the more we heat, the stickier the situation becomes, because there will be a larger and larger excess of sugar molecules which will not find an aqueous partner, creating a syrup. They tightly cling onto any remaining water, frantically scrambling around in an ever-accelerating chaotic dance, and so heat needs to become increasingly brutal: a thermometer will show that the boiling temperature will keep on creeping up as one continues to heat the syrup.
What does this mean? The longer one boils the syrup (or the higher the temperature reached), the lower its water content. Less water means a harder final product. Bear this in mind. Rule of thumb number one of the art of confectionery.
Without the company of enough water, there could be a way out for desperate, forsaken sugars: meet and cling onto one another, sinking back into a solid. But the heat keeps them apart in a violent motion, bouncing around and so sugars cannot get hold of one another. All it takes for a crystal to form is a slower rhythm – a drop in temperature – and some sort of trigger . Think of the sugar syrup as a boulder teetering on the brink: it just takes a light push to make it fall.
2 ) So, this concentrated hot syrup is primed to form sugar crystals: when the dance slows down and something helps sugars to bump into one another, a crystal will start growing. That’s why we talk about nucleation and growth when discussing crystallisation. These words sound dry and technical, but they can also tell the story of the most bittersweet flavour of life, stories of random encounters (nucleation) turning into ever more passionate love (growth). We love, and so do molecules, in their own way. The trigger, the nucleus, can be a minute crystal that has already formed, or even a foreign body, like some dust. Then, growing crystals vie with each other for the limited available sugar much as snow crystals do in clouds. It is at this stage that the cooling syrup requires the cook’s full attention.
3 ) That is because sugar crystals can grow to different sizes and shapes, much like snowflakes. So, although crystallisation is indeed ‘order out of disorder’, order itself can come in different versions. Think about boxes: either you stack them up in a single tall pile reaching to the ceiling, or you stack them in pairs but all over the floor.
So we have two main options: large but few, and small but many. What do they mean in terms of candy making?
Big is not beautiful
The hot syrup is a chaotic environment, every forsaken sugar cries and shouts and tries to draw their fellows’ attention, all of this while swirling wildly around. What a dramatic scene! It’s an unruly mob looking for a charismatic leader. Imagine that all of a sudden a voice resonates piercing through the hubbub: it speaks the loudest, it will be heard. The seed of unrest moves swiftly in the heated syrup, and quickly rallies supporters all around. No time for other groups to form: they are dispersed in the crowd. The mob clusters around its leader, ready to follow down that road, the road to crystallisation.
Big crystals form this way, when few seeds collect lots of sugar molecules, often as a result of the crystallisation starting too early when the syrup is still too hot. They contribute to a coarse, grainy texture in the candy, and feel chunky in the mouth. How to avoid them?
Call in the riot police
It looks like that the most finely-textured candy is similar to a pluralistic society: many little crystals all coexisting like many political activists voicing their opinion and gathering small groups of followers. It is (Zygmunt Bauman would approve of it) a fluid society.
All we need to do is to wait for the tempers to cool down, and then stir up some healthy agitation, slowly but continuously, to encourage the engagement of as many seeds as possible.
If a stirring stick is not enough, well, plan B is to draw the baton. So, another way to make sure that law and order reigns in the syrup is to rely on something that will forcefully prevent clustering.
Cooks have used additives to limit crystallisation, in jargon called ‘doctoring agents’, for a long time. They make sure that police cordons are thrown throughout the syrup preventing the clusters of people from growing. Crowd control in the kitchen.
If trained people can control other people’s unrest, sugars can control the crystallisation of sugars. Take note: this is a very important concept. Difficult to understand? Not really.
An exercise with dumbbells
Our everyday life is full of examples of activities involving packing, arranging, ordering things. Someone is tidier, someone is messier (like me): but if the form of the object to be packed does not help, well, it is a no-go. Sugar crystallisation in candy making, invisible though it is, provides just another example of it. How could you turn packing into a nightmare? Simply by adding a handful of oddly shaped items. Believe it or not, it is just the same for ‘doctoring agents’ in confectionery.
Table sugar is sucrose. It looks like a fixed-weight dumbbell with two equal weights, but of different colours. We call one half of it fructose, the other glucose.
So, because you have got two units, you can name sucrose a dimer. Say you are at the gym, and your have got to tidy dumbbells up, arranging them back on the rack. As long as the dumbbell is in one piece, that is piece of cake. But if the handle breaks and the two weights fall down, well, that is another cup of tea. Imagine that enough handles break, or that there are more weights than handles, and this is a recipe for disaster: you will never be able to fill the dumbbell rack. Game over.
Controlling crystallisation in candies rests on either of those two options: have more weights than handles, or snapping the handles to separate the two ways. The former just involves tweaking the sugar proportions, replacing some sucrose with glucose, for example. But chemistry is dead good at snapping handles, at breaking bonds: we will see later how to do this.
Right, enough theory and taxidermy of confectionery for now: let’s talk about the real stuff. Here are two sweet case-studies that have made me sweat and swear in the kitchen in the last few months: lokum (aka ‘Turkish Delights’) and torrone (hard nougat).
The same and not the same
Different as they might seem, chewy pink cubes versus rock hard white slabs, lokum and torrone come to the same critical crossroads: the mixing of hot syrup with the chosen scaffold halfway through the recipe. And both rely on some sleight of hand to avoid unwanted, untimely crystallisation.
Looking more closely6, here are a few differences:
It is an aerated candy, or, put it differently, a toughened egg white foam (a reinforced meringue): the most important step in its preparation involves streaming hot syrup into whipped egg white, while whisking.
Sounds easy? Maybe, but if you want to nail it, not only do you have to get the timing of the mixing right, you must also have a feeling for the intensity of the whisking motion. All of this while the white-hot egg+syrup goo gets splattered all over the kitchen. (See the picture at the start of this post. Like in the lab, safety first: wearing protective spectacles when working with syrup is a golden rule). At any rate, what matters from a chemical perspective is that nougat could be called candied protein: after all, this is what egg white is made of.
It belongs to the family of jelly candies: their chewy bite is determined by the added scaffolding. Cooks can choose between a variety of ingredients, many of them now widely available in supermarkets, too: agar (from algae), pectin (from fruit) and starch. Lokum relies on the latter, in the form of the humble cornflour.
Watch out: starch is a massively heavy counterpart of the sucrose/dumbbell that we talked about before. Individual weights can be stacked one on top of each other, or arranged in more convoluted ways. Whichever you choose, remember that sucrose was a di-mer a two-unit dumbbell. Starch is a poly-mer a multi-unit object, and losing sweetness is the price to pay when going from one to many. Sucrose was a two-colour dumbbell, with glucose and fructose as weights; instead, starch just contains glucose units. Just to crack the jargon, because we are talking about sugars, we can also say that starch is a poly-saccharide, which in plain English would sound like multi-sugar. So, if I called (tongue in cheek) nougat candied protein, let me say that lokum is candied multi-sugar, which is slightly scary in these days of low-carb hype.
To sum it up, have a look at this flow-chart showing the main steps in the preparation of lokum and torrone
I turned out the first batch of lokum one Sunday morning. This time, I decided to have a go at making lokum after reading a review on the production of these sweets7, something that sounds like what we often do in the lab: you come across a paper, an idea flashes, and off you go.
[…]The history of lokum dates back to more than 300 years, making it one of the oldest sweets in the world. Turkish legend has it that in his endeavor to cope with all his mistresses, a Turkish sultan summoned all his confectionery experts and ordered them to produce a unique dessert to add to the collection of the secret recipes for which he was famous. As a result of extensive research lokum was born. In 1776, during the reign of Sultan Abdul Hamid I, Hadji Bekir, a fully apprenticed confectioner, arrived in Istanbul from a small town in Anatolia. Bekir set up a little shop in the center of the city, and quickly won fame and fortune among the people. Fashionable ladies began to give lokum to their friends in special lace handkerchiefs. […] Lokum had been known in Anatolia since the 15th century, but it had become widespread in the borders of the Ottoman Empire[…] 7
Fascinating. Let’s have a look at how to make lokum using our scheme
|sucrose (table sugar)||cornstarch||red colour
|Cook syrup to…||How to add the scaffolding?
||When to add the inclusions?
|126-127°C||-Dissolve cornstarch in water.
-Add to hot syrup while stirring.
-Continue cooking until the mixture stops giving off steam.
|Last step before cooling down|
There’s one ingredient missing, and I left it out from the list on purpose. It is the famous ‘doctoring agent’ we were talking about before. To limit crystallisation in lokum, the sucrose-dumbbell is broken up by some lemon juice, or anything edible that has an acidic pH.
Sawing a dumbbell up into two pieces is not exactly the easiest pastime. Yes, it depends on how thick the handle is, but if your saw is not sharp enough, you will have to toil anyway. What about your own strength, then? Are your arms fit enough for the job?
As one can see, there is an interplay of three parameters to work out how efficiently we can break those blessed miniature dumbbells called sucrose. Let’s wrap it up:
- How thick the handle is, in chemical terms, how sturdy the bond between glucose and fructose is. It turns out that it is not so frail as it might look.
- How sharp the saw is: reactions happen, or not. Or we can make it happen, think about what we found out in the previous post about catalytic converters. Catalysis plays a role in making lokum, too: not only is the acidic pH of lemon juice a sharp saw, it also helps to corrode the handle, to slacken the bond.
- How strong your arm is: cooks have an advantage over lumberjacks: they can crank the heat up, which is what they do when the syrup is being cooked. Heat, the water “kidnapper” is also a powerful source of energy for chemical reactions to happen.
Despite the heat, the lemon juice, the amount of sucrose broken up is ridiculously small. Yet, it is enough to avoid untimely crystallisation: after all, lokum contains also a very effective scaffolding agent, starch.
Following the recipe step by step, I boiled the syrup, then I added the starch mixture, and kept on stirring while heating. A glossy, viscous mass was formed, and it started clinging onto the silicone spatula. Call it goo if you like, but this was beautiful in its own way.
Finally, I added the extra bits, some rose water and beetroot extract. Then, I poured the pinkish mixture into a baking tray and I let it cool down. As a last step, I chopped it up into small pieces with scissors (that seemed to be the smartest idea).
I asked a Turkish colleague to taste my lokum: she said that it was a good attempt, and, tastewise, it was close to the real thing. Unfortunately the texture was off the mark, too soft. A couple of days later she brought lokum back from Turkey, an ideal basis for comparison. See for yourself.
My error? The maximum temperature reached by the syrup during the cooking step. My kitchen journal provides irrefutable evidence of my mistake: the recipe that I followed did not mention the temperature and I just tried to make an educated guess: 118°C Only later did I find out8 that I should have heated the syrup up to…126-127 °C.
(If you’d like to try, too, follow this recipe.)
Torrone (hard nougat) is quite another cup of tea. I decided to make it because I felt homesick, back in December: this month sees the consumption of torrone skyrocket, and not only because of Christmas. In some parts of Italy, for example in the north-east, children get presents and sweet treats on St. Lucy’s Day (13th December).
When I found the recipe in a book 8, I could not resist the temptation: the fact that the text classified it as ‘difficult’, just provided some extra thrill. After all, “if there’s a will, there’s a way”, right? Here are the proportions and the operations, from the same recipe:
|sucrose (680 g)
honey (510 g)
corn syrup (170 g)
|whipped egg white||pistachios, almonds
orange blossom water
|Cook syrup to…||How to add the scaffolding?
||When to add the inclusions?
|150 °C||-Stream hot syrup into whipped egg white while whisking.
-Keep on whisking for a few minutes.
|-Keep them warm in the oven.
-Add to egg white + syrup mixture as last step.
This time, the ‘doctoring agent’ is corn syrup, also known as glucose syrup: it is a crystal-clear, thick fluid containing free glucose, which is one of the two components of sucrose, in a varying amount (10-43 %). So, instead of sawing up the dumbbell handles, we add in some extra weights that we cannot fit on the dumbbell rack.
The name corn syrup is a giveaway: it betrays the fact that this product is manufactured from cornstarch (which was the scaffolding of lokum). If you remember that I described starch as a collection of glucose units, that should not come as a complete surprise! In fact, corn syrup contains poly-glucose units of varying length. But…watch out! Honey contains free glucose, too, roughly one third in weight. This means that, regardless of the exact concentration of free glucose in corn syrup, we can approximate the glucose : sucrose weight ratio to 1:3.
Then, I skimmed through the advice given at the start of the recipe:
“Be careful to have all mise en place ready as per the instructions. Once you begin the process, it should not be interrupted until the nougat is cooling“
“Sugar cooking temperature is critical. Use an accurate thermometer and cook the sugars carefully”
Ok, here we go. I deployed all pots and pans that I thought I would need and I set about working. I shelled the pistachio nuts and I added them to the almonds, storing them in a bowl in the oven, set at a low temperature (120 °C). After that, I separated the egg whites, leaving them in another bowl with a pinch of cream of tartar.
Then it was time to start cooking the sugar syrup, without honey, which I heated in a second saucepan, as suggested by the recipe. At first, the temperature was creeping up slowly, degree by degree, on a gentle heat. Then, the rate of increase in temperature quickly sped up, the number on the display fast approaching the target temperature of 150°C. Time to make the egg foam, and do it fast. While keeping an eye on the thermometer, I whipped the egg whites until the foam looked stiff enough. 148…149°C…time was trickling away as the temperature rose higher and higher. When it reached 150°C, everything happened in the blink of an eye: I grabbed the saucepan with the hot honey and I poured it into the syrup: the temperature dropped slightly, but it bounced back incredibly fast. I placed the metal bowl with the egg white foam in the kitchen sink, I snatched the large saucepan brimming with syrup, my left hand firmly holding the electrical whisk in mid air. I turned the saucepan, a moment that seemed to last forever, as it looked as if gravity would fail me. Suddenly, a thin trickle dived into the fluffy white. Down, pour it down, stream it into the foam, whisk it in, wield that whip, draw figures of eight as a sweet sticky mess is splattered all around. I kept on whisking for a few minutes; after that, I added the hot mixture to the nuts that I had set aside. I carelessly tossed the metal bowl into the kitchen sink, where it landed with a clanging noise as I was reaching for the roasting tray that I had lined with rice paper. The nougat-to-be was starting to cool down, and so I had to rush. I shovelled the thick white fluid into the tray with a silicone spatula, the pistachios and the almonds barely emerging from the surface as rocks submerged in an ivory sea. I laid the top sheet of rice paper with utmost and loving care, as though I were wrapping the lying nougat in a shroud.
Some sugar-honey syrup had spilt onto my kitchen sink, and set into a glassy amber slab (you can spot it in the featured image above!). I sort of thought I would find a mosquito trapped in one of them.
Later on, after a few hours’ rest, I pried the nougat out and I cut it roughly into bite-sized chunks. It was not the hardest nougat ever, but it seemed almost spot-on, also considering the limitations of my equipment, and the fact that I could not possibly cook the egg-syrup mixture for as long as 12 hours 9.
Little did I know that the hardest part was yet to come. In fact, storing homemade nougat can be tricky because of the hygroscopic nature of this sweet. Sugars will absorb moisture, and the nougat easily starts to ‘weep’, becoming stickier and stickier in the process. Aware of this issue, I thought I would outsmart the nougat this time: I stored the pieces in an airtight (borosilicate) glass container, which I put in the freezer overnight, just to be on the safe side. On the following day, I shared the nougat with friends and it was a great success, despite its texture.
Then, at a certain point, I flipped the container over, and I spotted a chip, then a fault line, and eventually a spiderweb pattern of cracks. All the bottom part of the nougat was keeping the bottom of the container together, becoming effectively inedible in the process. I salvaged the top layer, but the rest was lost. What a pity.
Trying to get candies right often looks like the toil of Sisyphus, the mythological giant condemned to keep pushing a boulder uphill only to see it roll back down once more.
Yet, “One must imagine Sisyphus happy”, suggests the French philosopher Albert Camus10.
Absurd as it sounds, that is so true. Never can we be freer and happier than when we take up those apparently pointless challenges bound to end, or fail, like cooking, loving, writing a poem or tasting a candy, those most treasured pleasures of our one and only life.
The most bittersweet delight.
- Literally meaning ‘vast programme’, the closest English translation of this famous quote by De Gaulle is ‘a tall order’.
- “[…]sugar is expensive, a spice that, in the Middle Ages, is produced only in Sicily and Andalusia, where sugarcane is grown. […] In France, sugar is mentioned for its medical applications as of the early 1200s, but it is seldom used as a cooking ingredient until the 1300s […]”. O. Redon, F. Sabban, S. Serventi, La gastronomie au Moyen-Age. 150 recettes de France et d’Italie, Editions Stock, 1993, Paris
- Chemistry: The Impure Science, Bernadette Bensaude-Vincent and Jonathan Simon, Imperial College Press, 2012 (2nd edition).
- Rein Vihalemm, Philosophy of chemistry and the image of science, Foundations of Science, 2007, 12, 223-,
- English translation found online
- On Food & Cooking, Harold McGee, Hodder & Stoughton, 2004
- A. Baku and B. Kirmaci, Production of Turkish delights (lokum), Food Research International, 2009, 42, 1-
- P.P. Greweling, Chocolates and confections :at home with the Culinary Institute of America , 2010, Wiley
- See this Wikipedia page (in Italian). This long cooking is required to obtain the rock-hard texture of certain types of torrone which, when snapped, will break and splinter into tiny shards. I remember, as a child, playing with these sticky pieces that would invariably cling onto the tablecloth.
- “Il faut imaginer Sisyphe heureux”, Albert Camus, Le mythe de Sisyphe.