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Coffee and Tea

March 25, 2024

Women were sex objects well into the 1970s. Flight attendants were exclusively women; and, before laws were enacted to prevent employment discrimination, the requirements for a flight attendant were quite specific.
A high school graduate, single (widows and divorcees with no children considered), 20 years of age (girls 19 1/2 may apply for future consideration). 5'2" but no more than 5'9", weight 105 to 135 in proportion to height and have at least 20/40 vision without glasses.[1]
The perceived flight attendant culture of that period is expressed in the entertaining 1973 made-for-TV movie, Coffee, Tea or Me?, based on the book of the same title.[2-3]

Karen Valentine and Louise Lasser in Coffee, Tea or Me?

Karen Valentine as Carol Burnham-Byrnes and Louise Lasser as Susan Edmonds in Coffee, Tea or Me?

(Still image from a YouTube video.[2])

An intangible benefit of coffee is its ability to jump-start a person's working day, with a possible benefit to the gross domestic product (GDP). More tangible is the precise economic impact of the coffee industry. In 2022, coffee's impact on the United States GDP was $343.2 billion.[4] The U.S. coffee industry employs 2.2 million people, generating more than $100 billion in wages.[4] Consumers spent nearly $110 billion on coffee in 2022.[4]

Since scientists have done many experimental studies on the physics and chemistry of coffee, this blog has featured several articles about coffee.

•  Coffee Rings, December 10, 2010
•  Coffee Rings (Part II), August 25, 2011
•  Coffee Thermodynamics, June 17, 2011
•  Caffeine-Resistant Bacteria, January 7, 2016
•  Coffee Break, August 8, 2016
•  Coffee Acoustics and Espresso Foam, October 31, 2016

Mathematician, Paul Erdos

Mathematician, Paul Erdős (1913-1996).

Since he consumed large quantities of coffee, Erdős is often cited as the source of the quotation, "A mathematician is a device for turning coffee into theorems." This quotation is believed to have originated with another prominent mathematician, Alfréd Rényi (1921-1970).

(Wikimedia Commons image, modified for artistic effect.)

Coffee shops have become a popular way to get coffee, but it's more economical, and perhaps more environmentally friendly, to make coffee at home. At home, I use a Bunn drip coffeemaker, which is a step up from the typical home coffeemaker. I use whole coffee beans that I grind myself. I store the beans in the freezer to keep them fresh, and research has shown that there's another reason why you should keep the beans cold before grinding.[5] Cooling a material often makes it brittle, and this is true for coffee beans, giving smaller particles (see graph).[5]

Ground coffee particle size distribution at various temperatures

Ground coffee particle size distribution at various temperatures.

Note the logarithmic scale.

(Portion of Fig. 4a of Ref. 5, licensed under a Creative Commons Attribution 4.0 International License.[5]

A 2014 study examined the role of dissolved cations in coffee extraction, particularly dissolved Na+, Mg2+, and Ca2+.[6] The object of the study was to determine the ideal mineral composition of water for extraction of flavor compounds in coffee.[6] This 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. Aside from extraction, a pinch of table salt is often added to coffee to reduce bitterness by acting on the taste receptors of the tongue. I once noticed that the sugar packets in a diner were labelled as also containing salt.

Contrary to stereotype, Britons consume about twice as much coffee as tea.[7] Coffee is also more popular worldwide than tea.[7] Some Internet websites indicate that tea is the more popular drink, possibly based on outdated statistics. According to the British Coffee Association, about two billion cups of coffee are consumed worldwide each day.[7]

There have been fewer scientific studies on tea than coffee. The first tea study, "On the Infusion of Tea," was published in 1885 by the woman chemist, Wilhelmina Green.[8] Another woman chemist, Bryn Mawr College chemistry professor, Michelle Francl, has just published a book, "Steeped: The Chemistry of Tea," that summarizes tea science.[9-10] The book was released on January 24, 2024.[11] Francl is also an adjunct scholar of the Vatican Observatory.[11] Emmy Noether(1882-1935), an eminent mathematician and mathematical physicist, taught at Bryn Mawr from 1933 until her death in 1935.

Although Francl's parents were both coffee drinkers, she's been drinking tea since she was twelve years old.[11-12] She became interested enough to write her book when she noticed a tweet from a fellow chemist who asked whether a tetrahedral tea bag makes a better cup of tea than the standard tea bag.[11] Francl says that she tried to write the book to be accessible to non-chemists; and, her sister, who had never taken a course in chemistry said that "her eyes didn't glaze over" while reading the book.[11] Francl says that black Assam tea, with a lot of sugar. is her favorite tea, and that she enjoys the slow ritual of tea brewing involving boiling the water and waiting for the tea to infuse before drinking.[11]

One interesting tea fact is that black tea, green tea, and other teas differ not because of the plant species, but in the production process.[11] Tea is a cultural institution in the United Kingdom, and an estimated 100 million cups of tea are made there daily.[12] Francl says that she's "...had better cups of tea in gas stations in Ireland than... in really fancy restaurants in the U.S."[11] The main problem with restaurant tea is that the water is too cold for a good infusion. Hotter water releases more caffeine and aromatic compounds.[11]

Structural diagram of caffeine

Structural diagram of caffeine.

The US Food and Drug Administration (FDA) classifies caffeine as generally safe, with a recommended limit of 400 milligrams per day for a healthy individual. An eight ounce cup of coffee has about 100 milligrams of caffeine. Black tea has about 50 milligrams, and green tea has about 30 milligrams.

Caffeinated soft drinks can contain about 5 milligrams of caffeine per ounce, or about the same per ounce as coffee. Energy drinks can have more than 75 milligrams of caffeine per serving. The toxic dose of caffeine is more than ten grams (10,000 milligrams) in a day.

(Wikimedia Commons image by NEUROtiker. Click for larger image.)

One tea mystery that Francl writes about is the white film that appears on the surface of brewed tea if the water is heated in a microwave oven. This is related to the water's dissolved oxygen, which is removed in stovetop boiling, but not in microwave heating.[11-12] The oxygen reacts to form magnesium and carbonate precipitates of the tea chemicals, but adding lemon juice will prevent this reaction.[11] Francl also suggests adding a little salt, for the same reason as adding salt to coffee.[12] This is against British custom, and the Embassy of the United States, London, has released a perhaps humorous response that this technique is not official United States government policy.[12]


  1. Michelle Higgins, "63 Years Flying, From Glamour to Days of Gray," New York Times, March 17, 2012.
  2. Coffee, Tea or Me? (1973), YouTube video by Terry Dawson, May 1, 2017.
  3. Trudy Baker, Rachel Jones, and Donald Bain, "Coffee, Tea or Me? The Uninhibited Memoirs of Two Airline Stewardesses," Penguin Books (paperback reissue edition, June 3, 2003), 320 pp., ISBN: 978-0142003510 (via Amazon).
  4. The NCA U.S. Coffee Impact Report, National Coffee Association of U.S.A., Inc..
  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. Coffee beats tea as Britain's favourite beverage, research suggests, itv.com, August 21, 2023.
  8. Wilhelmina Green, "On the Infusion of Tea," Chemical News, vol. 6 (November 6, 1885), pp. 229-31 (Via the Internet Archive)
  9. Michelle Francl, "Steeped: The Chemistry of Tea 1st Edition," (Royal Society of Chemistry, January 24, 2024), 240 pp., ISBN:978-1839165917 (via Amazon).
  10. Chapter 1: A Cup of Chemistry, excerpt of ref. 9, Royal Society of Chemistry, DOI:https://doi.org/10.1039/9781837670383-00001.
  11. Nate File, "How science can help you make a better cup of tea and why a Bryn Mawr scientist wrote a book about it, Philadelphia Inquirer, January 19, 2024.
  12. James Gregory, "US scientist recommends adding salt to make perfect cup of tea," BBC News, January 24, 2024.

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