The microorganisms that give us our Easter treats
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More than 3 million tonnes of chocolate are produced annually worldwide, and at this time of year much of it will be made into Easter eggs. Most people know that chocolate is produced from cocoa beans, which are the seeds of fruits from the Theobroma cacao tree. What is less known is that cocoa cannot be produced without the involvement of hundreds of species of fungi and bacteria.
- Cocoa fruit being picked.
- Cocoa beans in a freshly cut cocoa pod. Credit: Aude, via Wikipedia
Because of the global popularity of chocolate, chemical analysis of cocoa and chocolate has given us much information about individual flavour component contributions. However, it is not possible chemically to reproduce the characteristic chocolate flavour spectrum that microbial fermentation gives to cocoa beans. This means without the hundreds of microbial species that ferment the Theobroma seed pods, there would be no cocoa beans, and no chocolate Easter eggs!
Microbiology and the hot cross bun
The yeast that play a major role in cocoa bean production also give us another Easter
treat, the hot cross bun. This is a leavened (raised) sweet bread roll that is spiced, studded with mixed dried fruit and marked on top with a cross. Hot cross buns are traditionally eaten at Easter on Good Friday in the UK, Australia, New Zealand, Canada, South Africa and some parts of North America. The history of eating hot cross at Easter goes back to the 14th century, but our understanding of the importance of microorganisms in making these seasonal treats is much more recent. Hot cross buns have a pleasant sponge like texture due to the presence of a microscopic fungus, the yeast Saccharomyces cerevisiae. When given sugars, Saccharomyces via fermentation generates bubbles of carbon dioxide which cause the dough to rise, and the hot cross bun to have a light, open texture. Yeast through release of their enzymes contribute to hot cross bun flavour, and during baking add nutritionally important B vitamins. Close relatives of Saccharomyces (brewers and wine yeast) also play leading roles in the production of the wines, beers and lagers drunk at Easter. Yeast also give us flavouring preservatives such as vinegar, and of course we eat them directly as marmite!
Dr Primrose Freestone is Senior Lecturer in Clinical Microbiology in the Department of Infection, Immunity and Inflammation.