It’s currently National Chemistry Week in the US (apparently, we only get National Chemistry Week once every two years here in the UK), and the theme for this year is ‘The Sweet Side of Chemistry’. This seemed like as good an opportunity as any to look at some confectionary chemistry! In this graphic, we look at the amazing versatility of sucrose, and how (combined with other ingredients) it can make candies as hard as lollipops, or as soft as fudge.
Whilst there are a huge variety of candies available, we can actually divide them into just two main categories: crystalline and non-crystalline (or amorphous). These designations are derived from the arrangement of the sucrose molecules within the candy, which is deliberately controlled during the candy-making process. Before we consider these categories, though, we need to consider how candy is made. The sugar will be mixed with the other required ingredients and water, then heated to a desired boiling temperature which influences the final sugar concentration. It is then allowed to cool – and it is the difference in the processes that occur during the cooling which dictate the type of candy formed.
Examples of crystalline candies include fudge, fondant, and nougat. In these candies, the sugar solution the candy is made from is heated to boiling point, then slowly allowed to cool. The cooling process is actually very important, as it’s at this point that crystals of sucrose form. The sucrose molecules can align and form large ‘lattices’ of molecules, with a regular repeating structure; stirring is avoided until the solution has reached a relatively cool temperature (around 40˚C), otherwise it interferes with and prevents crystal formation. The small, fine crystals of sucrose that are formed give texture – for example, in the case of fudge. They also generally lead to a smooth, creamy candy.
By contrast, in the case of non-crystalline candies, such as lollipops and toffee, we actively want to prevent crystal formation. This can be accomplished in a number of ways. Chemically, ‘interfering agents’ can be added to the sugar solution in order to prevent crystallisation – common additions include other sugars such as glucose and fructose, which, having molecules of a different size and shape, get in the way of the sucrose molecules and stop crystals forming. Other chemicals, particularly acids, can be added to break up the sucrose into glucose and fructose, which also prevents crystallisation. Other substances can act as ‘mechanical interfering agents’. These include fats and proteins.
The temperature to which non-crystalline candies are heated is generally higher than that for crystalline candies, and they generally contain higher concentrations of sucrose. Once non-crystalline candies have been cooked and cooled, they must be ‘ripened’ – this process involves storing the candy to allow the moisture level to rise slightly and redissolve any small crystals that have formed in the sugar solution. The result is a smooth candy, and often hard.
In short, then, it’s the careful manipulation of the crystallisation of sucrose that enables us to create such a wide range of candies. If this has left you hungry for more confectionary chemistry, be sure to check out one of the previous posts on the site on the chemistry of chocolate!
References & Further Reading