Today, July 20th, is apparently national lollipop day in the United States, and general news is… *waves hands* so it seems like a good excuse to write something with lots of pictures of brightly coloured sweets, right? Plus, sugar!
The idea of putting something sugary on a stick to hold and eat is an ancient one. The very earliest humans probably used sticks to collect honey from beehives. Later, the Chinese, Egyptians and people from the Middle East dipped fruits and nuts in honey and used sticks to make them easier to eat.
In the 17th century, boiled sugar sweets were made in England and, again, sticks inserted to make eating easier. This may be where the name “lollipop” originates, since “lolly” is a dialect word for tongue. Later, in the American Civil War era (early 1860s), some sources say hard candy was put on the tips of pencils for children. In 1931 an American named George Smith started making hard candies on sticks, and trademarked the name lollipop — but he reportedly took the name from a racehorse named “Lolly Pop”.
Enough history, let’s get to the chemistry! Lollipops are made of sugar, with added colours and flavours. I’ve talked about sugar before, and it’s always worth remembering that we tend to use the word rather loosely in everyday speech.
There’s more than one type of sugar: in particular, the three that are probably most familiar are glucose, fructose and sucrose. Glucose is a simple sugar, and the one you might remember from photosynthesis and respiration equations. It’s essential for life, and you quickly run into serious trouble if your blood glucose levels drop too low (just ask a diabetic).
Like glucose, fructose is a monosaccharide (the simplest form of sugar), and is often called “fruit sugar” because, guess what, it’s common in fruits. Sucrose is what we know as “table sugar” and is a disaccharide, made up of a unit of glucose joined to a unit of fructose. In the body, sucrose is broken up into glucose and fructose.
The primary ingredient in lollipops is usually sucrose, which can be persuaded (more in a minute) to set nicely to produce a hard, shiny surface. However, commercial lollipops often also include corn syrup, or glucose syrup, which contains oligosaccharides: larger sugar molecules made from a number of simple sugar molecules joined together. Typically, as the name “glucose syrup” might suggest, these molecules contain units of glucose.
It’s worth mentioning here that corn syrup/glucose syrup isn’t the same as “high fructose corn syrup” or HFCS, in which the glucose molecules have been converted into fructose. This product is cheap, sweet and commercially easy to use, but it’s also controversial. Excessive consumption has been linked to obesity and non-alcoholic fatty liver disease, although the actual evidence is weak: a systematic review in 2014 concluded that there was little evidence it was worse than other forms of sugar. It’s really a problem of quantity: it’s easy and cheap for food manufacturers to throw HFCS into foods and drinks, and of course it tastes delicious, so as a consequence consumers end up eating too much of the stuff. In short: more water and fruit, less cake and fizzy drinks.
But having done the obligatory “eat healthily” thing, one lollipop isn’t going to hurt, is it? So back to that…
When it cools, sugar forms two different types of solid: crystalline and glassy amorphous (sometimes described as ‘amorphous solid’). Now, you might imagine that sugar as a crystalline solid is found in hard sweets/candies, but, no — it mostly turns up in soft things like fudge and fondant, which contain lots of very tiny crystals, giving an ever-so slightly granular texture. (An exception is rock candy, where the sugar is encouraged to form large crystals.)
The glassy amorphous form of sugar, on the other hand, can be literally like glass: hard, brittle, and transparent. In fact, “sugar glass” has in the past been used to make windows, bottles and so on for special effects in film and television, because it’s much less likely to cause injury than “real” glass. However, it’s very fragile and hygroscopic (meaning it absorbs water, causing it to soften over time) so these days it’s largely been replaced by synthetic resins.
The glassy amorphous form of sugar is achieved by starting with a 50% sugar solution which also contains an inhibitor, to prevent crystals forming spontaneously. Common inhibitors are the corn syrup I mentioned earlier, or cream of tartar (potassium bitartrate), honey or butter.
Exactly which you use depends on the recipe, but they all do essentially the same thing, namely, get in the way of the glucose molecules and prevent them ordering themselves into a regular (crystalline) structure. The mixture is heated to a high temperature (about 155 oC) until almost all the water evaporates — the final candy will only have about 1-2% water — and then cooled until glass transition occurs.
This is the clever bit, and only happens if crystallisation is inhibited (else crystals form instead). Glass transition happens around 100-150 oC below the melting point of the pure substance. For example, the melting point of pure sucrose is 186 oC, but it undergoes glass transition at around 60 oC.
Glass transition is a reversible change, which we might (if I didn’t generally dislike the concept) call a physical change. It’s a change of phase, where the sugar mixture changes from liquid to solid, but it’s different from crystallisation, because instead of the molecules becoming more ordered, they simply ‘freeze’ in their random, liquid positions. (It is, for the record, annoyingly difficult to show this in diagram form.)
Amorphous solid structures are sometimes called “supercooled liquids”. This isn’t wrong, but personally I think it’s unhelpful (and can lead to nonsense about glass flowing very slowly over time). Once cooled and set, glass, whether window glass or sugar glass, is absolutely not a liquid; it’s a solid.
Of course, to make lollipops, all sorts of colours and flavours are added to the mixture as well, and sometimes more than one mixture is used to create intricate, layered effects. There are even medicinal lollipops which contain, for example, the powerful painkiller fentanyl — the idea being that the patient can administer the dose gradually as needed.
Which brings me to the end. Happy National Lollipop Day! My favourites are Chupa Chups — if you’ve enjoyed this, how about popping over to Ko-fi so I can stock up? And if you’ve been eating sweets, do remember to clean your teeth!
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