5 things serious coffee fans should know

The day might also be an opportunity to look at the science behind the beverage that 63% of Americans drink daily (more than tap water), according to the National Coffee Association.

Here are five facts you should know if you consider yourself a coffee connoisseur…

1. Coffee doesn't exactly wake you up — it blocks the neurotransmitter that makes you sleepy.

• Without caffeine, the neurotransmitter adenosine typically binds to adenosine receptors to slow down cell activity and make you feel sleepy.
• But caffeine can bind to those same receptors and block adenosine, so cells speed up instead of slowing down as usual (that can lead to positive or negative side effects, depending on who you are).
• Caffeine might also increase dopamine levels.

2. A morning cup of coffee can activate parts of the brain involved with short-term memory and focus, according to a new study.

• Certain brain changes were only attributable to coffee and not just caffeine, the Frontiers in Behavioral Neuroscience study suggests.
• That's thanks to the placebo effect — or the experience of drinking coffee — the researchers found.
• That's just the latest news from an endless stream of coffee studies, which also includes this report about living longer.

3. Decaf does have some caffeine and requires a soaking process that may or may not involve chemicals.

• The decaffeination process removes about 97% of the caffeine in coffee beans (as required by the FDA), so there's still about 2–15 mg of caffeine in a decaf cup, depending on the brand. Note: There's around 95 mg in a caffeinated cup of joe.
• The process of turning regular unroasted beans into the decaf variety involves soaking the beans in a hot liquid to dissolve the caffeine.
• Some coffee companies just use water for decaf, and others employ water and a liquid carbon dioxide or a chemical solvent like methylene chloride. The FDA has recognized the latter as safe in such minuscule amounts, but that process can be controversial.

4. Dark and light roasts have similar caffeine content.

• Dark roast coffee is made from beans heated to higher temperatures and for longer than lighter roasts, but caffeine content across roasts is comparable.

• The extra roasting and chemical reactions mean a more intense smell and taste in dark roasts, and it might cause a small amount of caffeine to be lost, according to Healthline.
• But dark roast beans are smaller than lighter ones — so they could have more caffeine by volume compared to lighter roasts, but less per bean.

5. Coffee likely won't dehydrate you if you have fewer than five cups daily.

• Coffee — which is mostly water — may have hydrating qualities, according to some studies.
• As a diuretic, coffee does make you pee more than usual, but research suggests that the fluid intake from caffeinated beverages typically balances out the liquid lost through extra urine.
• It might have a slight dehydrating effect if you consume more than 500 mg (more than five cups) of caffeine a day, though.

Go deeper: Coffee, the healthy indulgence

Editor's note: This story has been corrected to note that coffee blocks the neurotransmitter (not hormone) that makes you sleepy.