R&D LAB
Dr Monika Fekete is the Founder of Coffee Science Lab.
A bittersweet experiment Dr. Monika Fekete shares a home experiment to demonstrate how activated charcoal can remove the bitterness from coffee.
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’m taking these challenging times as an excuse to indulge in online shopping for locally crafted beans, and to play with home-based coffee experiments. Rather than sacrificing homedelivered specialty goodness for these experiments, I turned to supermarket coffee. The description on the bag of beans I’d bought described the coffee as “medium roast”. I brewed the coffee with a chemex and tasted the whole bitter segment of the coffee flavour wheel: harsh caustic bitterness combined with pungent phenolic bitterness. There are some pleasant nutty and malty aromas, but the experience was dominated by those persistent bitter flavours.
So where does bitterness in coffee come from? According to a report in Science magazine, food chemists at the Technical University of Munich discovered chlorogenic acids (CGA) present in green coffee to be the main culprits behind coffee’s bitterness. CGAs are not bitter in their natural forms. However, as the roast progresses, a chain of reactions convert CGAs to chlorogenic acid lactones (a group of about 10 chemicals) responsible for some mild, but not unpleasant, bitterness. Roasting the beans further breaks the lactones down to a group of chemicals called phenylindanes that cause harsh bitterness, a characteristic of dark roasted coffee. In addition, according to the
Figure 1. USB microscope image comparing the grain size of “fishtank” and medical charcoal to coffee grinds.
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beanscenemag.com.au
authors of this study, caffeine accounts for around 15 per cent of coffee’s bitter taste. But is there a way we could remove these bitter tasting compounds from coffee at home without using laboratory chemicals and sophisticated equipment? Activated charcoal comes to mind, as it’s commonly used for the removal of phenolic contaminants from wastewater. This is good news as CGAs and their breakdown products are also phenolic compounds. It’s even used in the Swiss water process for removing caffeine from green coffee. But what is it exactly and how does it work? Activated charcoal, or active carbon, is made by heating plant materials, such as coconut husks, to high temperatures in a low-oxygen environment, a process called pyrolysis. The charred material is then “activated” using oxygen or steam. Basically, the process creates tiny cracks and pores, dramatically increasing the surface area. Just one gram of activated carbon has a surface area of 500 to 3000 square metres, comparable to the size of a football field. That’s a lot of area for molecules to attach. Activated carbon acts like a sticky sponge for gases and chemicals, and it has wide usage from water purification to medical treatment for acute poisoning. Medical or food grade activated charcoal is safe to take in small amounts. It’s also safe to drink coffee filtered through it, as we will do in this experiment. However, it’s not recommended to ingest too much as it can strip food from its nutrients. This leads us to another important point about activated charcoal: it’s not very selective. A large range of molecules can stick to it. In the following experiment, I will show you how activated carbon can
