Christmas means different things to different people. For me, it’s an opportunity to eat celebratory foods that aren’t available all year round.

The top of my list is glazed ham, but a very close second is a well matured Christmas pudding with different dairy-rich trimmings.

But what chemical transformations are involved in making a Christmas pud? Here’s the science.

A Christmas pudding is a steamed dessert consisting of dried fruits, sugar, flour, fats, spices, eggs and alcohol. It is often cooked well in advanced and left to mature, then steamed or reheated before serving.

Modern puddings tend to use dried grapes (raisins, currants and sultanas) and candied fruits such as cherries and citrus peel.

Dried fruits have different flavour profiles compared with fresh fruits. Many of the volatile flavour compounds are lost but new flavours develop. These can be formed by enzymatic browning (like when cut fruit turns brown), reactions with light, and transformations of fatty acids and even natural colours into flavour compounds.

Candied or glacé fruits such as cherries and citrus peel are made by heating the fruit in a sugar syrup. The water content of the fruit is replaced by sugar, leaving a chewy, sweet, but less colourful product.

This sugary environment is inhospitable to microbes. The water from bacteria and fungi is removed on contact with the sugary surface due to a process known as osmosis.

Dried fruits for a Christmas pudding........

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