How Does Coffee Work?

Coffee Chemicals

Coffee and work. Work and coffee. For millions, these are two inseparable ideas. We sip coffee while we work. Our coworkers display desktop kitsch to remind us of their dependency on caffeine. Our bosses even spend company money making sure the office brewing apparatus is well stocked. Coffee is oil for the hourly-wage machine. As a matter of fact, it is the second most important commodity in the modern world, right behind oil. We know that we work on coffee, but how does coffee work?

Growing and processing

The bitter brown drink brewing on our countertops every morning goes through a variety of natural and artificial changes before it scalds our tongues. That process starts with a plant which could be any of 66 species in the Rubiaceae family. The variety Coffea arabica, from which 2/3rds of all coffee cups are brewed gloablly, yields quality coffee with considerable caffeine. 

Ripe Coffee Cherry or Berry
Ripe Coffee Cherry or Berry From Filo gèn', CC BY-SA 4.0 , via Wikimedia Commons

Coffee only works because of the natural compounds that develop in its fruit. Before the cherry is ripe, the bean lacks the proteins that would eventually give the drink its aroma and taste. These proteins will make up around 10% of coffee’s weight. Once ripe, the berry is notable for its thick cell walls made of cellulose, which help to pressure cook the compounds inside when roasted. These make up almost 50% of the weight of green coffee. The soluble carbohydrates like fructose and glucose in the bean help to thicken coffee’s texture, hold flavor in the brew, and stabilize foam. Importantly, the alkaloid caffeine makes up between 1-4% of dry coffee’s weight. Nevertheless, eating coffee cherries won’t help us meet our deadlines.

These compounds are not readily available to the groggy drinker. The berry envelops the useful bean in several layers: pericarp, mesocarp, mucilage, endocarp, and finally endosperm. In more common terms, there is a skin surrounding a pulp surrounding a membrane surrounding a parchment, surrounding a “silver skin.” Once the cherry is harvested, these must all be removed in succession to avoid rotting and to extract the potent pit. The cherries are pulped, dried, threshed and sometimes polished before being sorted and bagged as green coffee for roasting. 

 

Coffee berry structure
1: center cut 2: bean (endosperm) 3: silver skin (testa, epidermis), 4: parchment (hull, endocarp) 5: pectin layer 6: pulp (mesocarp) 7: outer skin (pericarp, exocarp From Original version: Y tambe. Vectorized by: Chabacano, CC BY-SA 3.0 , via Wikimedia Commons

Roasting and brewing

After nature has produced the compounds and man has whittled down the product, roasting and brewing further transform the natural chemicals. Roasting coffee cooks many of the natural compounds of the coffee bean into aromatic and soluble ones. The layer next to the bean, the silver skin, is burnt off entirely if it had not previously been polished off (as in some expensive coffees). Complex polysaccharides break down into simple sugars. Above 185°C, Maillard’s reaction begins. This is caramelization during which sugars and proteins combine. In coffee, this reaction produces its deep brown color and signature bitter flavor. It also gives off carbon dioxide. Around 40 compounds in a finished coffee roast will add to its flavor and aroma. Careful, if coffee is under-roasted, carcinogenic compounds such as acrylamide can form and remain if not roasted away. 

Roasting takes the natural chemicals of the coffee bean and transforms them into water-soluble aromatic compounds. After grinding, the brewing process puts large amounts of surface area in contact with hot water, priming the grounds for extraction. The majority of the soluble compounds in the roast coffee beans will dissolve in the water within minutes. These compounds make coffee what it is: stimulating caffeine, bitter flavonoids, astringent soluble acids, and brown melanoidins. Different percolation methods will arrive at different concentrations of each compound. Espresso, for instance, uses high pressure and tightly packed grounds to limit the acids that pass into solution. The temperature of the beverage is important, as hot water increases solubility of these compounds and helps the body uptake caffeine. 

 

from Annerella, CC BY-SA 3.0 , via Wikimedia Commons
from Annerella, CC BY-SA 3.0 , via Wikimedia Commons

Drinking and Stimulation

Coffee is harvested and processed, beans are roasted and ground, a cup of piping hot joe sits on the counter and we take a sip. Now, the compounds that came from coffee and were transformed during roasting enter the body and begin to take effect. 

Alkaloids, in this case caffeine, help the body to release adrenaline and increase intercellular communication. These special compounds interfere with the production and reception of the enzymes that regulate our nervous systems. Nervous signals are actually stronger because alkaloids inhibit the degradation of important neurotransmission enzymes. In other words, coffee keeps us awake because it stops our body from taking compounds that act as messengers out of circulation. Of all the alkaloid compounds that humans consume, caffeine is the best at stimulating our central nervous system, helping us to stay alert and work our day away. 

Because of the increase in nervous activity, the body uses more energy. Drinking coffee increases our metabolisms and actually stimulates the body’s consumption of fat cells for energy. One study concludes, “the ingestion of as little as 50mg of caffeine by normal-weight, non-exercising, healthy men produced a significant increase in resting energy expenditure within 30 minutes of caffeine ingestion. The increase persisted for at least 4 hours and produced a significant 6% total increase in daily resting energy expenditure.” (Glade). Once in our body, coffee heightens all of our nervous activity. We experience this as a rush of energy, but we are actually consuming more energy because of it.

Drinking coffee does incredible things to the body. Our blood pumps quicker, we have a better mood, and we are quicker to react. More blood pumps through our brains, our endurance is prolonged,  and our short-term memory is optimized. Coffee, even the decaffeinated stuff, increases rectosigmoid motor activity and makes us want to poop. While many of these effects are good, caffeine can also cause addiction and insomnia. The chemicals in coffee, now well studied, are just as active in our body as they make us feel.

Most of us couldn’t work a day without coffee, and as it turns out coffee wouldn’t really work without us. The fruit that grows on a coffee bush will not deliver the desired effect that a porcelain saucer of espresso will. Humans must intervene in the natural state of affairs to transform these natural compounds into a cup of coffee. We do this by stripping the fruit down to its most potent part, rendering the compounds soluble and aromatic with heat, dissolving the compounds in water, then introducing them into our bodies by drinking. In short, coffee is the result of a complex series of reactions and interactions. When we brew a morning cup of joe, we can pat ourselves on the back—we are really masters of chemistry. 

 

Mikael Häggström, CC0, via Wikimedia Commons
Mikael Häggström, CC0, via Wikimedia Commons

Sources Cited

Barreiro, Eliezer J., Arthur E. Kümmerle, and Carlos AM Fraga. “The methylation effect in medicinal chemistry.” Chemical reviews 111.9 (2011): 5215-5246.

Brown, S. R., P. A. Cann, and N. W. Read. “Effect of coffee on distal colon function.” Gut 31.4 (1990): 450-453
Esquivel, Patricia, and Victor M. Jimenez. “Functional properties of coffee and coffee by-products.” Food Research International 46.2 (2012): 488-495.

Glade, Michael J. “Caffeine—not just a stimulant.” Nutrition 26.10 (2010): 932-938

Illy, Ernesto. “<em>The Complexity Of</Em> Coffee.” Scientific American, vol. 286, no. 6, Scientific American, a division of Nature America, Inc., 2002, pp. 86–91, http://www.jstor.org/stable/26059726.

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