Chemical and physical considerations in coffee production with Christopher Hendon

Chemical physical considerations coffee production Christopher Hendon

Professor Christopher Hendon wrapped up the 15th instalment of Toby’s Estate’s Knowledge Talk in Sydney on 12 November, where he discussed chemical and physical considerations in the production of coffee.

Christopher currently works at the University of Oregon, which has nicknamed him Dr. Coffee, though his professional relationship with coffee actually began while studying at the University of Bath in the United Kingdom.

“In 2014, I walked into a famous café, Colonna & Smalls, owned by Maxwell Colonna Dashwood and his wife,” Christopher says.

“I was greeted by a board displaying the varietal, origin, and tasting notes of espresso drinks on the left and filter on the right. I tasted this first espresso, which had fruitcake as a flavour, and it made me wonder, ‘does that come from being a natural, from Brazil, or the varietal every time?’”

Christopher now estimates that, generally, 50 per cent of cup quality can be attributed to the green bean, 10 per cent to equipment, and 20 per cent to roast and water chemistry. However, he and Maxell initially believed water chemistry could be a determining factor.

“We initially attributed this to water, but after many years working with this industry, I’ve realised what is more likely causing variations in cup quality is variations in the green bean we start with.”

Christopher and Maxwell’s work to understand the role of water chemistry in coffee flavour was published in Water for Coffee, with an updated edition soon to be released.

“The [major factor in water chemistry] that matters is bicarbonate, because its job is to destroy acids. If you expose water continuing bicarbonate to acids, it will do its very best to make sure you can’t taste them,” Christopher says.

Christopher Hendon with the Toby's Estate team.
Chemical physical considerations coffee production Christopher Hendon

Christopher recommends that cafés in areas with high water hardness focus on producing espresso base drinks over filter, which contain similar levels of extracted coffee but significantly less bicarbonate.

More recently, Christopher has worked on developing a mathematical model to predict the results of espresso extraction. Assuming coffee has been roasted adequately, he focused his first step on how the grind impacts coffee extraction. Part of this was examining the relationship between fines – small particles – and boulders – large particles.

“The grind setting determines the large particle sizes, while the dust is determined by how many cracks you make. What’s quite challenging is, as you grind finer, the boulders get smaller while the small particles grow in population,” Christopher says.

“We discovered that cooling coffee down will decrease size while homogenising the particle size. This is because when the coffee is really cold, the crack will easily find path of least resistance through the bean.”

Next, Christopher analysed the relationship between grind setting, using a Mahlkönig EK, and extraction yield. According to his model, extraction yield should continue to increase as the grind becomes finer. However, when implemented practically with Michael Cameron of St Ali, they found channeling began to occur when the grind size reached 1.5 on the EK43, meaning some part of the pucks were overextracted and others under, leading to inconsistent yields.

Michael also identified the tasty point as at 1.3 on the grinder, at 22 per cent extraction.

Due to the “volcano” shape of the graph, Christopher suggests this this shot could be made more reproducible using the coarser 1.9 setting with the same extraction yield.

“The obvious thing you could do is grind coarser and hit that 22 per cent extraction yield every single time, but it would come at the deficit of the shot running a lot faster than you were used to,” Christopher says.

“Because at 1.3 the coffee puck is unevenly extracted, it could also still taste different. But if you want your shot to be reproducible, you’ll need to stick to the coarser side of the graph. This is a bit problematic because the shot runs fast and the beverage volume goes down.

Christopher adds that reducing dose size will also increase extraction, as more water will come into contact with the coffee. He suggests reducing dosage from the standard 20 grams to closer to 15 while grinding coarser, meaning less coffee is used while more is extracted from it.

“There is a tremendous economic upside to be had for espresso,” Christopher says.

“In a Melbourne café, 500 espresso drinks a day is about 182,000 a year. If you implement this reduction from 20 grams 15 grams, while pushing the extraction yields up, you’ll save yourself $24,000 just from that reduction in coffee mass.”

Ultimately, Christopher encourages baristas to taste the coffee they are producing to determining what works.

All proceeds from the ticket sales of Knowledge Talks will be donated to the Las Nubes Daycare and Afterschool-Learning Centre. The centre supports the education of over 40 children aged between three and 12 in the coffee community of Acatenango.

On a daily basis the centre provides much needed education, nutritional meals and a safe and nurturing environment while allowing the parents to continue working or to complete their education.

For more information, visit

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