How Does Pre-Soaking Affect Coffee Aroma? - Chromatography Explores

Coffee drinking is on the increase. Even in the tea loving UK, almost 100 million cups of coffee are drunk every day. A significant increase in the last ten years. And whilst most of this coffee is the instant variety drunk at home, the amount of coffee shops adorning the high streets of towns and cities suggest that there is a significant increase in the amount of coffee brewed directly from beans.

Producing a great cup of coffee is more an art than a science - but that doesn’t mean science doesn’t have a role to play in fine tuning the process. Work published in Flavour Science highlights how chromatography could help improve the aroma of roasted coffee beans.

It’s all in the beans

There are two main types of beans used to give us our daily cups of fresh coffee - Arabica and Robusta. They account for most of the coffee production in the world with 61% and 38% respectively. Arabica beans are perceived as giving a higher quality brew with better flavour, aroma and colour. Consequently, they attract a higher premium.

But to create a specific aroma or taste, Robusta beans are sometimes blended with Arabica beans. Robusta beans are also blended to help reduce the costs as Arabica beans cost more. But the Robusta beans can impart a less desirable odour, a ‘muddy’ odour and can also affect the flavour. Subsequently the maximum amount of beans that can be blended is limited.

Improving the roast - can chromatography help?

To improve the quality of Robusta beans they are sometimes pre-washed or steamed to remove the compounds that cause the ‘muddy’ aroma. A team from the University of Nottingham investigated how much the pre-wash beans have before roasting can affect the aroma of the beans after roasting. The rich aroma and flavour we associate with coffee beans comes during the roasting process. Then complex chemical reactions take place. But does the pre-washing reduce the amount of amino acids, sugars and other precursors needed to make delicious smelling coffee?

The team tested both Robusta and Arabica beans by pre-soaking the beans in water (2-12 hours) at different temperatures (20-100ËšC) - the team also tested non-treated beans. After pre-treatment and weighing the beans were roasted at 200Ëšfor 20 minutes before being ground and stored in a freezer before analysis by gas and liquid chromatography. The importance of sample preparation in food sample analysis is discussed in the article, Vacuum Assisted Headspace Solid-phase Microextraction: A Powerful Tool for Olive Oil Analysis.

The team found that increased soaking temperature decreased the protein content of the beans - whilst the beans non-soaked Robusta beans had a significantly higher sugar content compared to the soaked beans. All aroma compounds showed a reduced concentration as the soaking time and temperature increased. For better coffee, don’t soak. But how to get rid of the ‘muddy’ aroma?