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Why does candy floss dissolve in water?
Dip a stick of candy floss in water and the fluffy cloud shrinks to nothing in seconds. It looks like magic, but it comes down to two things: how fine the sugar threads are, and the unusual form the sugar is in. Here is the science.
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Candy floss, also called cotton candy or fairy floss, is sugar that has been melted and spun into threads, usually with only a little flavouring and colour added. All of its sugar is spread out in fine strands: see how is candy floss made?
How the threads are made
In a candy floss machine, a spinning head melts sugar and flings it out through tiny holes. Food scientists at the University of Minnesota describe the process as melting crystalline sugar above 210°C, then shooting the liquid sugar into the air, where it cools so fast that it sets as an amorphous, glassy solid rather than as crystals.
Reason one: a huge surface
How fast a solid dissolves depends on how much of its surface the water can reach. The Noyes Whitney equation, worked out by the chemists Arthur Noyes and Willis Whitney in 1897, links the rate at which a solid dissolves to its properties, including its surface area.
A sugar lump has a small surface for its size. Candy floss is the opposite: the same sugar is drawn out into countless hair fine threads, so a great deal of it is at the surface. When it meets water, the water reaches all of it at once, and the cloud collapses almost instantly.
Reason two: glassy sugar
Ordinary sugar is crystalline. The sugar in candy floss is amorphous: it set so quickly that it never formed crystals. The amorphous form of a substance can be more soluble than its crystals: some amorphous medicines, for example, have been shown to be absorbed better than their crystalline forms for that reason.
The same reason it hates damp air
The glassy sugar that makes candy floss dissolve so easily also makes it hygroscopic: it pulls water out of the air. That is why candy floss shrinks, goes sticky and then turns hard and crunchy if it is left out: see why does candy floss go hard?
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Questions and answers
Why does candy floss dissolve so fast?
Because its sugar is spun into extremely fine threads, which give it a huge surface for water to reach, and the rate a solid dissolves depends on its surface area. The sugar is also in a glassy, amorphous form rather than tidy crystals.
Is candy floss just sugar?
Mostly. It is made by melting sugar and spinning it through tiny holes, and it usually contains only small amounts of flavouring and colour.
Why does candy floss shrink in damp weather?
For the same reason it dissolves so easily. The glassy sugar is hygroscopic, so it takes up water from the air, and in humid conditions it collapses and crystallises within a day: see why candy floss goes hard.
Sources
- Cotton candy, Wikipedia
- Influence of temperature and relative humidity on the physical states of cotton candy, T. P. Labuza and P. S. Labuza, 2004, Journal of Food Processing and Preservation, via University of Minnesota
- Arthur Amos Noyes, the Noyes Whitney equation, Wikipedia
- Amorphous solid, Wikipedia
Keep reading
- Sweet tips and how toWhy does candy floss go hard?Candy floss is glassy sugar that pulls water from the air. Then it collapses and crystallises into hard lumps, in under a day in humid air.
- How it is madeHow is candy floss made?Candy floss is sugar melted in a spinning head and flung through tiny holes, where it cools into fine threads. The machine was invented in 1897, by a dentist.
- The people behind the sweetsThe dentist who invented candy flossCandy floss was invented by a dentist. In 1897 William Morrison of Nashville and sweet maker John C. Wharton built a machine that spun sugar into fairy floss.
- Questions people askIs candy floss vegan?Usually, yes. Candy floss is spun sugar with a little flavouring and colour. Check the colour, as carmine comes from insects, and where the sugar is from.
- Sweet tips and how toHow to make candy floss without a machineWithout a machine you can still spin sugar: boil it to 155°C, then flick the syrup from a fork over a rolling pin into fine threads. How to do it safely.
- Sweet tips and how toWhy does seaside rock go soft?Rock goes soft and sticky because sugar pulls moisture out of the air. Here is the science, and how to keep a stick of rock hard for longer.