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Coffee Break

August 8, 2016

As they say, "you are what you eat," which is reason enough for me to avoid vegetables. This expression is the title of a 1940 book by Victor Lindlahr, but the phrase is actually much older. It was written in 1826 by the French gastronome, Anthelme Brillat-Savarin, as "Tell me what you eat, and I will tell you what you are."[1] This may be more a commentary on the cost of healthy food, rather than its health benefits.

While healthy eating is important to us all, it's usually hard to determine what is healthy to eat, and to eat just those items. My father-in-law was a lentil lover, and lentils are considered to be healthy fare, but he enjoyed his Sunday barbecue, too.

The circa 12th century Regimen sanitatis Salernitanum was the health food manual of its time. It contains the following gems:[2]
• If you develop a hangover from drinking (alcohol) at night, drink again in the morning; it will be your best medicine. (Our modern "hair of the dog" remedy.)

• If you add wine to pork, then it is food and medicine.

• If your head is feverish or aches, milk is not very healthy.

• Beer nourishes thick humors, gives strength, fattens the flesh, produces blood, provokes urine, has a laxative effect, causes gas, and has a cooling effect.

• Rue makes man chaste, intelligent and cunning. When cooked, rue makes the house safe from fleas.

• Phlebotomy is scarcely needed before a person is seventeen... Phlebotomy cheers the sad, calms the angry and helps cure madmen.

As I race to my next phlebotomy, I pause to think about the recurrent problem that what's considered healthy one year is found to be unhealthy the next, and subsequently restored to healthy status in a subsequent year.

One example is butter, which was at one time vilified, then restored to its previous grandeur when it was discovered that the trans fats of margarine were likely worse. Alcoholic beverages are another example, with alcohol consumption linked to a panoply of diseases, but small quantities appear to show benefit against heart disease for older individuals.

As a coffee drinker who limits himself to one cup a day, I've always read the latest health reports on coffee. These have generally been ambiguous, but the World Health Organization (WHO) has just reported its assessment of coffee's affect on health based on clinical evidence accumulated in the past 25 years.[3-4]

coffee bubbles

Carbonated coffee?

Have you ever noticed that coffee sometimes has bubbles on its surface?

This indicates fresh coffee.

(Wikimedia Commons image by Salim Fadhley .)

The WHO concluded that coffee is not a carcinogen, and it seems to protect against liver cancer and uterine cancer to some extent.[3-4] The WHO does advise that drinking excessively hot beverages (about 70°C), including coffee, is linked with cancer of the esophagus, which is the eighth most common cause of cancer worldwide, causing 5% of all cancer deaths.

Now that I can more happily drink my coffee, my concern is how to prepare it to get the best taste. As I wrote in a previous article (Caffeine-Resistant Bacteria, January 7, 2016), I use a Bunn, which is a step up from the typical coffeemaker. I grind the coffee beans fresh. While I store the beans in the freezer to keep them fresh, recent research shows that there's another reason why you should keep the beans cold before grinding.[5]

As most materials scientists and mechanical engineers know, cooling a material often makes it brittle. There are many examples on YouTube of objects that shatter with the slightest impact when cooled to liquid nitrogen temperatures (-196°C); however, most of these items are a cheat, since they contain water. As tragically demonstrated by World War II liberty ships in the cold waters of the North Atlantic Ocean, certain steels will become brittle at temperatures below about -50 °C.

Coffee beans become brittle at low temperatures, and this affect was investigated by scientists from Meritics Ltd. (United Kingdom), St Ali/Sensory Lab (Victoria, Australia), Mahlkönig GmbH & Co. (Hamburg, Germany), Has Bean Coffee Ltd. (Stafford, United Kingdom), University of Bath (Bath, United Kingdom), the University of Southern California (Los Angeles, California), The University of Melbourne (Victoria, Australia), and the Massachusetts Institute of Technology (Cambridge, Massachusetts).[5] Colder beans produce a greater numbers of fine particles that lead to enhanced flavor extraction (see graph).

Figure caption

Ground coffee particle size distribution at various temperatures.

Note the logarithmic scale.

(Portion of Fig. 4a of Ref. 4, licensed under a Creative Commons Attribution 4.0 International License.[4]

The experimental results, shown above for El Salvadorian coffee, gave 61 ± 3 μm particle size for -196 °C, 63 ± 3 μ for -79 °C, 73 ± 3 μm for -19 °C, and 70 ± 3 μm for 20 °C. This might not seem like too large a change, but the surface area scales as the square of these values, and the higher the surface area, the faster the extraction.

Brewing coffee beverage requires water, so what qualities of water are needed for the best brew? At home, I use water that's filtered through a Brita filter, a necessity for our well water. The Brita filter contains activated charcoal that removes organics and some inorganic salts; and an ion exchange resin to remove carbonates and other metal compounds.

In 2014, a computational chemist from the University of Bath (Bath, U.K.) and a barista champion from the specialty coffee shop, Colonna and Small's (Bath, U.K), published research on the role of dissolved cations in coffee extraction.[6-7] They looked particularly at dissolved Na+, Mg2+, and Ca2+. They looked at the binding energies of these ions to five acids contained in coffee, to caffeine, and to a representative flavor component, eugenol.[6] The object of their study was to determine the ideal mineral composition of water for extraction of flavor compounds in coffee.[6]

The reason why these cations are important in coffee brewing is that electron-rich heteroatoms, such as nitrogen, oxygen, sulfur, phosphorous, chlorine, or bromine, are parts of "coffee molecules," and these should interact strongly with the dissolved cations in water. Coffee contains about 500 such chemical compounds, and water with a high concentration of cations should facilitate a greater extraction of coffee flavors.[7]

The cation factor is known in the coffee industry, and an ionic concentration of 150–300 parts per million (ppm) is generally recommended for coffee extraction.[7] This recommendation assumes that all cations have equivalent affect, which is not true. The paper, unfortunately, does not give a recipe for an ideal coffee brewing water. A pinch of table salt is often added to coffee to reduce bitterness, but this salt acts on the taste receptors of the tongue, and it is not related to the salts involved in the extraction process.

3D molecular model of caffeine

I drink coffee for the flavor, but many drink it for its caffeine content.

In this molecular model of caffeine, carbon = black, hydrogen = white, oxygen = red, and nitrogen = blue.

(Via Wikimedia Commons.)


  1. In French, "Dis-moi ce que tu manges, je te dirai ce que tu es." The meaning and origin of the expression: You are what you eat, from The Phrase Finder.
  2. Latin text of the Regimen sanitatis Salernitanum can be found at the Wellcome Library Web Site. An English translation can be found as a PDF file at the Society for Creative Anachronism, Australia.
  3. Dana Loomis, Kathryn Z Guyton, Yann Grosse, Béatrice Lauby-Secretan, Fatiha El Ghissassi, Véronique Bouvard, Lamia Benbrahim-Tallaa, Neela Guha, Heidi Mattock, and Kurt Straif on behalf of the International Agency for Research on Cancer Monograph Working Group, "Carcinogenicity of drinking coffee, maté, and very hot beverages," The Lancet Oncology, Advance Online Publication, June 15, 2016, DOI: http://dx.doi.org/10.1016/S1470-2045(16)30239-X.
  4. IARC Monographs evaluate drinking coffee, maté, and very hot beverages, WHO International Agency for Research on Cancer Press Release no. 244, June 15, 2016.
  5. Erol Uman, Maxwell Colonna-Dashwood, Lesley Colonna-Dashwood, Matthew Perger, Christian Klatt, Stephen Leighton, Brian Miller, Keith T. Butler, Brent C. Melot, Rory W. Speirs & Christopher H. Hendon, "The effect of bean origin and temperature on grinding roasted coffee," Scientific Reports, vol. 6, article no. 24483 (April 18, 2016), doi:10.1038/srep24483. This is an open access article with a PDF file here.
  6. Christopher H. Hendon, Lesley Colonna-Dashwood, and Maxwell Colonna-Dashwood, "The Role of Dissolved Cations in Coffee Extraction," Journal of Agricultural and Food Chemistry, vol. 62, no. 21 (May 28, 2014), pp. 4947-4950, DOI: 10.1021/jf501687c.
  7. Chris Hendon, "Schrödinger’s water for the perfect cup of coffee," Chemistry World Blog, Royal Society of Chemists, May 30, 2014.

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