Coffee's chemical brew

For most people, the day begins with the odor of 2-furylmethanethiol, guaiacol, 3-mercapto-3-methylbutylformate and numerous other chemical compounds which make up the aroma of a good, rich cup of coffee. Whether home-brewed or store-bought, a cup of coffee is a ritual which makes getting up in the morning bearable.

Coffee is predominantly water, approximately 98.75 percent, with the remaining 1.25 percent being extracted plant material. (Of course, this is presuming the absence of sugar and milk which lower the water content very slightly.) Hot water is a superb solvent for the extractable oils and acids found in a coffee bean. Over 2,000 chemical compounds are extracted from the roasted bean in the process of making a cup of coffee but a cup of coffee is still predominantly water. As caffeine is a diuretic, for new coffee drinkers, they quickly excrete the excess water. For seasoned coffee connoisseurs, a new water balance in the body is established.

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While chemical names often frighten or intimidate people, most chemical compounds are not bad for you. Indeed, everything you eat and drink is made up of a myriad of chemical compounds. Some are even quite beneficial. For example, coffee contains 3,5-dicaffeoylquinic acid which has been demonstrated to protect neurons from free radical oxidation in the lab. This would certainly suggest coffee has anti-oxidant potential.

It is estimated the world drinks two billion cups of coffee per day. The Netherlands tops the list with a per capita consumption of 2.4 cups per day compared to Canada at 1.01 and the U.S. at 0.93. Of course, per capita consumption is based on the total population and not just coffee drinkers. However, for most countries, about half of all adults indulge in the drink. In North America, this gives an average of about 2.6 cups per day for consumers. And it is big business - a $12 billion per year industry.

In essence, coffee is a combination of oils, salts, acids, and other compounds which give rise to the distinctive and complex flavour. Extracting these compounds from the roasted coffee bean is the art of the barista. Generating a consistent taste can be complicated. However, a recent paper published in the journal Matter provides insights into "Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment".

he authors argue the grind and water pressure used in making the drink are critical to producing high quality and consistent results. They suggest new brewing protocols can both produce a better cup and reduce the amount of coffee required in making an espresso. However, they recognize their results might seem counterintuitive.

Any extraction process requires contact between the material being extracted and the solvent doing the extraction. In the case of coffee, this is the roasted bean and hot water. And intuitively, the larger the surface area of the ground up bean grains, the more effective the extraction process. Hence, the tendency towards a very fine grind in making espresso.

If homogeneous flow occurred, the relationship between surface area and total extraction would hold. However, the results of mathematical modeling demonstrate this is not the case inside an espresso machine. In experimental measurements, peak extraction is achieved with a medium grind while lower, more inconsistent extraction is achieved with both fine and coarse grinds. The results suggest inhomogeneous flow for the fine grinds with clumping and permeability affect the quality of the cup.

Using a local coffee shop as an experimental site, the authors were able to show a coarser grind, a lower pressure, and a shorter extraction time produced both a better and a more consistent cup of espresso. Further, they were able to reduce the mass of coffee beans required from 20 grams to just 15 grams. While this might not seem to be a huge difference, in their test environment the reduction in coffee bean consumption resulted in a savings of $3,620 dollars.

The total cost of the coffee in an espresso is 10 cents, so a 25 per cent reduction in coffee mass would be a savings of 2.5 cents per cup. In the United States, 124 million cups of espresso are consumed daily resulting in a savings of $3.1 million dollars per day or roughly $1.1 billion per year. Further, a reduction in the coffee mass consumed per cup would result in a decrease in the demand for coffee growing which would reduce pressure on farmland. An economic and environmental argument could be made for brewing better espresso.

In addition to the above suggested extraction regime, one of the authors, Christopher Hendon, suggests using hard water as the calcium and magnesium help caffeine adhere better improving the taste and quality of the drink, keeping coffee beans in the refrigerator as this prevents off-gassing and choosing your grinder carefully to get the right setting.

All in the name of the perfect cup of joe.

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