Millions of people rely on caffeine every day to stay alert and improve concentration. Caffeine is also added to energy drinks although the actual amount of caffeine is greater in a cup of coffee. A brewed 8 oz. cup of coffee contains 95-200 mg of caffeine and a 1 oz. espresso contains 47-75 mg. (1)
According to Mayo Clinic up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults (2).
Health benefits of caffeine --Caffeine, in moderation, can have positive effects. For regular coffee drinkers, these include a decreased risk of developing Alzheimer’s and dementia, certain cancers, strokes, Parkinson’s, and decreased suicide risk (by 45%). On a daily level, studies have shown caffeine can boost concentration and memory levels... see About Caffeine.
Many people consider drinking a dark roasted coffee to get the benefit of more caffeine. This however is a myth. Caffeine is extremely stable during the roasting process.
"...So when do differences in caffeine content come into play? This happens when roasted coffee is measured for brewing or packaging. Since a bean loses weight (mainly water) during roasting, its caffeine content by weight increases while its caffeine content by volume decreases. Confused yet? Let’s put this principle into practice by measuring some coffee. Dark-roast coffees measured by volume with a scoop actually contain fewer coffee beans due to their larger size, resulting in a weaker brew and less caffeine per cup than a light-roast coffee measured in the same manner. Bottom line, you're not getting the most from a dark-roast coffee if you measure it by volume..."(see reference 3)
The density of the bean changes; beans that are roasted longer are less dense due to loss water. Note: Unroasted beans sink in water while roasted beans float in water. If you measure your coffee by scoops, light roasted coffee will have more caffeine since light roasted beans are denser than a darker roast. However if you weigh out your scoops, darker roasts will have more caffeine, because there is less mass. see reference (4)
Coffee floats mostly due to trapped carbon dioxide, which is a by product of the roasting process. The fresher the coffee, the more likely grounds are to float, since this gas gradually dissipates over the course of the weeks and months following roast. (4)
"... It is well known that limited sunlight exposure and elevation have a significant positive effect over bean density, making coffee beans harder and heavier, the natural causes of light restriction could be several: latitude, canopy shade and aspect (topography) are among the main ones. However, it is definitely shade and elevation the two most important of them all..." (5) .
"...Specially, the altitude at which coffee is grown plays a major role in determining the quality of the green coffee bean, because there is less oxygen, coffee plants grown at higher altitudes take longer time to mature than plants grown at lower altitudes. This allows the flavors to develop more fully and produces beans that are delicate and flavorful. High altitudes grown coffee beans usually have a high density than low altitudes grown coffee beans.." (6).."
"...RESULTS: Coffee from high altitude with open or medium shade and early to middle harvest periods gave superior bean quality. These growing conditions also favoured production of beans with lower caffeine. Increasing altitude from mid to high, ca. 400m decreased caffeine content by 10%. At high altitude, dense shade decreased Q1 coffee by 50%. Compared to late harvesting, early harvesting increased the percentage from 27 to 73%. At mid altitude >80% is Q2 coffee. Conclusions: Changes of quality scores driven by altitude, shade and harvest period are small, though may induce dramatic switches in the fraction Q1 vs. Q2 coffee. The latter affects farmers' profit and competitiveness in the international markets..." source (7)
Generally, beans of coffee trees grown at higher altitudes usually have a higher density than beans of coffee trees grown at lower altitudes (Sridevi & Giridhar, 2014). (8)
High altitudes above 900m to 1500m and beyond provide ideal growing conditions for the coffee tree. Cooler mountain temperatures provide a slower growth cycle for the coffee tree which prolongs bean development. This longer maturation process provides the coffee bean with more complex sugars, yielding deeper and more compelling flavors. In aiddition the better drainage at high elevations reduce the amount of water in the fruit resulting in a further concentration of flavors. The soil in which the finest Arabica coffees are grown is extremely fertile and often volcanic providing for exceptional flavor.
The coffee plant contains caffeine as a means to protect itself. Caffeine is toxic to most pests, so the caffeine acts as a natural pesticide. The arabica plant, which contains around half the caffeine content of robusta, has to grow at higher altitudes where fewer pests live. The robusta plant is able to survive even at sea level because the caffeine levels are so high in the plant.
"...In plants, caffeine acts as a natural pesticide that paralyzes and kills many insects feeding upon them. Caffeine is a central nervous system (CNS) stimulant, having the effect of warding off drowsiness and restoring alertness..."(9)
Coffee is know to contain over 1000 chemical compounds that contribute to both the taste and aroma of coffee. Although Caffeine is the most well know molecule and although is a bitter compound, it only contributes about 15% of coffee's bitter compounds. (10) Caffeine does however bind to adenosine receptors in the brain which is causes a stimulant effect. Caffeine is a poor prototypical bitter taste stimulus because it acts on bitter taste receptor-independent pathways, and caffeinated products most likely stimulate “taste” receptors in nongustatory cells. (11)
In a research study done by Thomas Hofmann, Ph.D., a professor of food chemistry and molecular sensory science at the Technical University of Munich in Germany.-- the main source of bitterness is from two sources: chlorogenic acid lactons and pheylindanes. Both the lactones as well as the phenylindanes are derived from chlorogenic acid, which is not itself bitter. Chlorogenic acid is found in the green unroasted coffee bean.(12,13)
According to Hoffman, roasting is the key factor driving the bitter taste in coffee beans. So the stronger you roast the coffee, the more harsh will tends to get. We've known for some time that the chlorogenic acid lactones are present in coffee, but their role as a source of bitterness was not known until now," Hofmann says. Ironically, the lactones as well as the phenylindanes are derived from chlorogenic acid, which is not itself bitter.(12,13)