What do you get when you combine sugar and science? Some pretty delicious food, that’s what.

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Sugar has a really bad reputation at the moment. Even though cost-cutting corporations stuffing us with high-fructose syrup is the real story behind obesity and diabetes. It is sugar that takes almost all the rap.

But sugar is not a poison. A bit of sugar is fine, in moderation.

Natural foods like milk, honey and fruit are stuffed with sugar. And where would we be mentally without the occasional choc-chip cookie?

What we need to do is take responsibility for our own sugar intake. We need to avoid the sugars that others add to our food.

We do that by making more of our food for ourselves.

I know, none of us has the time to run our kitchens like an 18th century farm-wife. But the more we manage to cook for ourselves, the less we need to rely on the good, or otherwise, practices of multinational food corporations.

Besides, if you only eat the fudge you find the time to make, if you are anything like me, you’ll eat much less fudge.

What is Sugar? The Basic Chemistry of Carbohydrates

If you are a chemist a sugar is any molecule that is, roughly, made up of carbon (C), hydrogen (H) and oxygen (O) in a specific ratio (technically called the stoichometry) of C_x(H₂O)_x.

That is for each carbon atom (C) in a sugar there is a water molecule (H₂O). In fact the scientific name for a sugar, carbohydrate, means ‘watered carbon’.

It’s a very loose definition, so don’t be confused if you come across sugars that don’t have this exact ratio. We’re not really that concerned with the stoichometry of carbohydrates in the kitchen anyway. If it says sugar on the label, it’s a sugar.

Monosaccharides vs. Disaccharides: Building Blocks of Sweetness

Carbohydrates are commonly divided into four broad groups according to their size. When looking at sugars, the two important ones are:

• Monosaccharides: the basic building blocks of carbohydrates. They are single sugar molecules like glucose, fructose and galactose.
• Disaccharides: are formed by two monosaccharides. Sucrose, common table sugar, which is formed by one glucose and one fructose molecule is a disaccharide. Other disaccharides include lactose, the sugar found in milk, that is formed by one glucose and one galactose molecule and maltose, which we normally encounter in corn syrup, which is formed by two glucose molecules.

What we commonly refer to as sugar are either monosaccharides or disaccharides.

More complex carbohydrates are not generally called sugars but they are also important and we have come across some of them before.

When attached to proteins, they are the cause of Maillard reactions that make for a nice sear on a steak. Starches are also carbohydrates and we have them to thank for our french fries.

How Sugar Dissolves in Water: The Mechanics of Hydration

That one is easy, right, when you put sugar in water it dissolves. But this is science, so there are complications.

When we looked at emulsions we saw that something dissolves when water interacts with charges, including partial charges, on a molecule.

When it comes to sugars, all those hydroxyl groups (the OHs) are ideal for forming electrostatic bonds with the water molecules.

So when we add solid sugar crystals to water, over time, sucrose molecules will gradually stop interacting with other sucrose molecules and will instead be surrounded by the more numerous water molecules in process we call hydration.

Saturation, Supersaturation, and Temperature

The ability of water to hydrate sugar relies on there being enough water molecules to completely surround every sugar molecule.

If we continue adding sugar, more and more water molecules will be needed to hydrate the additional sugar and eventually we’ll get to a point where all of the water molecules are hydrating sugar molecules.

When the solution gets to this point we call it a saturated solution, the amount of water in the solution can not hydrate any more sugar. If you add more sugar it will just stay in it’s solid form.

This applies to any substance that is soluble in some liquid. The solubility of any substance is the amount of it that you can dissolve in a liquid at a given temperature.

Temperature Matters

Notice that I qualified the previous sentence by referencing temperature. An important thing about solubility is that it is temperature dependent.

Generally, if you increase the temperature you increase the ability of a solvent to dissolve another substance.

This is certainly the case with sugar and water. If we heat water and then add enough sugar to saturate the solution, all the sugar will dissolve.

If we remove the solution from the heat and let it cool we will have more sugar dissolved in the water than the water is capable of hydrating. When this occurs we call the solution super-saturated.

As you would expect, this state of affairs is not ideal from a free energy perspective and if a supersaturated sugar solution is disturbed the sugar will begin to crystallise. Enough of the sugar will come out of solution, as we say, to make the solution a saturated solution again.

Crystals and Crystallisation

A crystal is just describes a solid in which the molecules are arranged into a regular, repeated pattern.

Many things form crystals, salt and sugar are common in the kitchen, and compounds that form crystals will naturally begin to crystallise when they start to come out of solution in a super-saturated solution.

If a substance doesn’t form crystals then they wont crystallise when it comes out of solution. For these compounds precipitation is a similar process, but sugar forms crystals so that’s what we’re looking at today.

Why Crystallisation is Important

In the modern world, crystallisation is a crucially important technique.

One way of purifying compounds from mixtures containing impurities is to heat a mixture, and by evaporating the solvent, you force the concentration of your compound above its saturation point and obtain pure crystals once the mixture is cooled.

Walter White did exactly this to purify his compound of interest in Breaking Bad, but it is also used in all sorts of perfectly legal industrial processes. Sugar production being one of them.

What Has All This Got to do With Making Dessert?

OK, I’ve gone on a lot about solvents, solutes and crysatallisation. What has all this got to do with making candy, sweets fudge and syrups?

The important thing to realise is that sugar cookery is all about getting a fair amount of sugar dissolved in water and then, often, controlling the crystallisation of your super-saturated sugar solution.

Syrups

At room temperature you can dissolve two parts sugar into one part water. If you heat this solution you’ll make the sugar dissolve faster but you won’t end up with a supersaturated solution.

If you want to make a thicker, and sweeter, solution you need to add more than two parts sugar then heat the solution. Once cooled you’ll have a super-saturated solution. But, as we saw above, it won’t be particularly stable.

I discuss physical ways to avoid crystallisation below, but one way you can stabilise your super-saturated syrups is to add some glucose or fructose. This is how naturally occurring syrups like honey and maple syrup, that crystallise relatively slowly, are stabilised.

Glucose and fructose insert themselves in-between the sucrose molecules that are trying to crystallise. This prevents the sucrose from crystallising.

You can achieve the same effect by adding some acid to your syrup, something like lemon juice or cream of tartar when making your syrup.

The heat and the acid cause the breakdown of some of the sucrose into glucose and fructose which then act as “inverted sugars” to stabilise the super-saturated syrup.

You don’t need heat to make syrup

In fact you don’t need to heat a syrup at all, you can make a syrup by just putting some sugar into water and letting it sit for a while. A 1:1 mixture of sugar to water will take about 15-20 minutes to dissolve whereas a 2:1 mixture will take about 45 minutes (Serious Eats has a good article about it). The downside is that if you are going to store your syrup and you don’t heat it you can end up with a syrup that rapidly spoils.

Understanding Sugar Crystallisation in Confectionery

Syrups are one thing, but sometimes you really want to super-saturate your sugar solution. This is particularly so if you want to make caramel, fudge or candy (or sweets if you live in the UK or lollies if you are in Australia or New Zealand).

The usual way to do this is to continue heating your syrup so that the water starts to boil and starts evaporating. As water leaves, in the form of steam, your sugar becomes more concentrated.

This is when working with sugar becomes tricky.

The boiling point of water increases with the amount of things dissolved in it. So, as you continue to boil your sugar solution the temperature is rapidly getting well above 100$\degree$C.

The hotter the syrup gets the quicker the water boils off, increasing the concentration and so the temperature rises again.

When you’ve got a rapidly boiling sugar solution at a temperature well above 100$\degree$C it’s not only a little dangerous, should you spill that solution on yourself, but it’s is also very easy to lose control and burn everything.

We can, of course, stop this process at any time and the amount of water that is left in the solution dictates how runny our cooled syrup will be and thus what we can use it for: a caramel sauce, fudge, or lollies.

Stage	Temp Range	Sugar Concentration	Common Culinary Uses
Simple Syrup	Room Temp – 100°C	50% – 66%	Cocktails, cake soak, iced tea
Thread Stage	106°C	80%	Glazes, preserves, candied fruit
Soft Ball	112°C – 116°C	85%	Fudge, fondant, pralines
Hard Ball	121°C – 130°C	92%	Marshmallows, nougat
Hard Crack	149°C – 154°C	99%	Hard candies, toffee, brittles
Caramelisation	160°C – 182°C	100% (Decomposing)	Caramel sauce, flan, spun sugar

What is a Nucleation Site?

Once we’ve made a super-saturated sugar solution what we need to do is control the crystallisation that is going to occur as the solution cools.

Sometimes we want to prevent crystallisation completely, if making hard boiled lollies for example. Otherwise, we want to make our crystals as small as possible. The larger the sugar crystals the grainier whatever we are making will be.

To start crystallising, the sugar needs something called a nucleation site. A nucleation site is physical place where the sugar can undergo a phase shift. In this case from a solute in a liquid to a solid.

A nucleation site can be microscopic scratches in pots or pans, dust particles, tiny air bubbles, or tiny crystals that form from splatters onto the side of the pan that are stirred back into the mixture.

Using a metal spoon can create nucleation sites by conducting heat away from localised parts of the solution, making them supersaturated, and even just agitation or stirring can encourage crystallisation by knocking the sugar molecules together and creating a nucleation site.

It stands to reason that if we want to avoid crystals we want to avoid giving our solution any nucleation sites. Or, given that crystals that start forming at higher temperatures are larger, controlling when nucleation sites become available.

What this means from a practical standpoint is that when we are cooling our syrup down we want to avoid agitating the solution, use a wooden spoon and wipe away any dried sugar from the side of the pan and stirring implements.

This is why when making fudge, for example, you let your syrup cool down before initiating crystallisation by stirring and continuing to stir until it’s cooled down and no longer workable.

Other Ways of Controlling Crystallisation

When you are working with sugar you are going to be adding other ingredients. A lot of these additives can also help prevent crystallisation.

I’ve already talked about inverted sugars, so honey or high fructose corn syrup, is often added to control crystallisation. Which is why you’ll see more than a few fudge recipes using corn syrup on the internet.

Likewise, milk and cream with their rich cargoes of fat and protein will tend to reduce sucrose crystallisation and because they are added while the syrup is still hot Maillard reactions will occur between the sugars and the milk proteins which adds some flavour.

Think caramel sauce for example where the sweetness of the sugar is combined with Maillard flavours and the mouth-feel of milk fats.

Caramelisation vs. Maillard Reaction: What’s the Difference?

Finally, the other thing that is happening at high temperature is the breakdown of sugar itself.

When making your sugar solution by the time you get to 165$\degree$C your solution will be almost 99% sugar. At this temperature sugar will start to break down into a variety of different molecules.

So, things like toffees and caramels, where you really cook down your syrup, will be coloured and have a distinctive flavour because of the new molecules that are being formed by the breakdown of the sucrose molecules.

This is similar to the Maillard reaction but, unlike when you “caramelise’” your steak, this is true caramelisation which is a sugar only event.

The browning you get from the Maillard reaction depends on the interaction of proteins and sugars. So saying you are caramelising your steak is probably the wrong thing to say.

This is something that infuriates scientists when watching cooking shows but it’s not something, I’m sure, that bothers anyone else in the slightest.

Conclusion

So, it turns out that a whole range of delicious dishes, from crème brûlée to fudge to boiled lollies all depends on the curious chemistry of sugar when you dissolve it in water and subject it to large amounts of heat.

Armed with this knowledge we can expand what we are able to do in the kitchen. We can impress our family and amaze our dinner guests with our mastery of sugar.

Most of all we can start making things that we thought we could only buy and so have a much better idea of how much sugar we, and our families, are consuming.