Figuring out the chemistry behind a great-tasting cup of coffee has been our number one goal as humans ever since we nailed sliced bread. If you’re a lover of coffee, then you’ll probably already know that not all coffee is created equally, and rarely are two cups ever the same.
But how can two cups be so different? It’s the same thing, coffee, but yet at the same time, each brew can produce entirely unique experiences. So why’s it so hard? Because there’s a ton of complex chemistry involved, that’s why!
We all know and love coffee for the caffeine, but caffeine doesn’t affect the flavor of your coffee. Brewing a great-tasting cup requires excellence in three parts: the roast, the bean, and the brew. Let’s take a look at the coffee chemistry.
Coffee Chemistry: The Components
The humble cup of coffee contains more than 1,000 chemicals, and while scientists haven’t figured out each and every one, they have nailed the big players when it comes to taste and potential health benefits.
Due to the popularity of coffee drinking, caffeine is a psychoactive drug taken by millions of people worldwide. YES, caffeine is a drug!
Caffeine helps to reduce fatigue, enhances perception, and gives you that extra kick to help you stay awake; some studies have even concluded that caffeine may help long-term memory.
In addition to keeping you awake and alert, caffeine is also linked to boosting energy expenditure and metabolic rate. When it comes to how much coffee you can drink in a day, dietary recommendations suggest that up to 400 milligrams of caffeine per day is perfectly fine.
Studies have shown that this bitter-tasting alkaloid can block cancer cells from moving around the body, protect the brain from damage, help to lower total cholesterol and sugars, and combat bacteria.
There are around 45 phenolic compounds that have been found in coffee. Along with their breakdown product, caffeic acid (1), these compounds have been shown to have anti-inflammatory and antibacterial properties, help lower type-2 diabetes, and aid in cardiovascular disease prevention.
Kahweol and Cafestol
It’s these diterpenes (2) that are the reason why your coffee tastes bitter. These compounds have been shown to prevent and aid in battling cancer. The bad news is that they have also been linked to raising your cholesterol.
The Secret Behind Great Tasting Coffee
So now you have a better understanding of some of the compounds found in coffee, let’s take a closer look at the beans, the roast, and how to brew a great-tasting cup.
Coffee farmers devote a lot of energy and time into growing and harvesting coffee trees (yes, that’s right, coffee does grow on trees) to make sure you get that perfect cup of joe. If you didn’t know, the coffee bean is actually the pit of a cherry. After these cherries are pitted, the coffee bean is dried and processed.
There are basically two bean varieties of commercially viable coffee beans the Arabica beans (Coffea Arabica) and Robusta beans (Coffea canephora var. Robusta). However there are roughly 70+ types of Coffea (the plants that produce coffee beans), but most are not palatable.
If you want the best-tasting coffee opt for the Arabica beans since they have a wider variety of aromas and balanced flavors. Arabica beans also tend to have more trigonelline and diterpenes (kahweol and cafestol).
If you want a cup of coffee with a bit more kick, the Robusta beans have almost twice as much caffeine and chlorogenic acids but do tend to have a more bitter taste.
The roasting process involves taking green coffee beans and turning them into delicious, toasty brown beans. The roasting also helps to bring out flavors like floral notes, chocolate, and more.
There isn’t a standard method that every coffee roaster follows when roasting coffee beans. But typically, coffee beans are roasted in a multi-step process from anywhere between 150 to 250 degrees Celsius and from 2 to 25 minutes.
150 to 200 Degrees Celsius
The first stage, at around 150 to 200 degrees Celsius, is when the Maillard Reaction (3) occurs. Proteins and sugars react to form aroma and flavor compounds during this reaction. Maillard chemistry isn’t just part of the coffee world; it’s also partially to thank for the excellent browning, flavor, and smell of other foods like fries, steak, and, of course, bacon (…mmm, bacon).
The Maillard reaction also helps create many other compounds, including 2-Furfurylthiol (4), which gives coffee its delicious roasted flavor.
170 to 200 Degrees Celsius
As the temperature slowly rises to 179 to 200 degrees Celsius, caramelization starts to take place, the natural sugars caramelize, and the generated compounds create burnt sugar (furanone’s) and butterscotch (diacetyl) flavors.
At 205 Degrees Celsius
When the temperature starts to reach 205 degrees Celsius, the water inside the bean begins to vaporize, which in turn causes the bean to expand and eventually crack open. This is known as the “first crack” in the coffee world.
At the first crack, “light roast” coffees are removed from the roaster. Light roasts tend to be higher in acidity, and the characteristics of different bean origins are most pronounced in light roasts.
225 to 230 Degrees Celsius
As the beans continue to roast and the temperature starts to reach 225 to 230 degrees Celsius the bean cracks once again; this is called the “second crack.”
This second crack results from the cellulose in the coffee bean’s cell walls breaking apart.
As it gets hotter, the bean starts to turn a much darker brown; at this stage, you have the favored medium roast. Medium roasts have a good balance between acidity from the bean and body from the roasting chemistry. Aromatic compounds also emerge, giving coffee an earthy scent and earthy, roasted flavors.
Even More Heat
Roasting any further will make the beans darker, and they will become pretty oily, and you’ll get your dark roast. At this stage, almost all of the tasting notes will be from the actual roasting, and you can’t tell the origin of the coffee bean at this stage because the strong body overwhelms those geographic notes. Darker roasts are typically used for brewing espresso.
So you’ve got all those coffee bean choices on the shelf, but how do you actually brew the best coffee you can?
Now you’ve arrived at the weakest link. You’ve got a coffee bean with a great origin and a roast you love. Now all that’s left is to grind it and add hot water, right? If only it were that easy. Unfortunately, you can have the best coffee in the world and still mess this part up.
There are a few critical components to brewing a great cup of coffee. There’s the coffee, the water ratio (ditch the tablespoon, better to use a coffee scale), then there is water quality (forget tap water use filtered or bottled water). You’ve got the water temperature, boiling water that is too hot, and you’ll get gross burnt coffee, so it’s best to get your water temperature close to 96 degrees Celsius (205 F).
Don’t forget you also need to decide how you will be brewing your coffee. There are pour-overs, Moka stovetop coffee makers, the Chemex, and French Press coffee makers (cafetière, press pots), to name just a few, but whatever you choose, the basic principles of all brewing methods are the same.
Chemistry Of Coffee Brewing
So you have chosen your best coffee maker, now for the coffee grind size. For the coffee grind, research shows that the more pulverized the beans, the more you’ll get out of them, caffeine, that is.
In one study (5), researchers found that using a regular home coffee grinder for 42 seconds compared with 5 seconds doubled the amount of caffeine squeezed out of a 37-gram portion.
Another study (6) found that having more particulates (the fine powder that turns into coffee sludge) also helped to increase the overall caffeine content.
As you add your water to your ground coffee, it spreads across the grounds, and CO2 starts to bubble out; this process is called the “coffee bloom.” Once the grounds are fully saturated, the hot water will begin to dissolve the compounds found in the roasted cells of the coffee beans.
Most of the delicious compounds will dissolve in water more readily than the nasty ones, so make sure to add enough water to get the good stuff to dissolve, but not too much that your coffee tastes terrible.
Finally, Osmosis will start to drag those compounds out of the coffee grounds and into the water, bringing all of those great flavors into your coffee pot.
Coffee geeks will tell you that manual pour-over coffee brewing methods like the Chemex or the Hario V60 are far better than automatic coffee brewers. This is true when brewing coffee the manual way. You have much more control over the brewing process and can tweak things on the fly, like how much water gets added and when.
Plus, pour-over methods continuously replenish the coffee grounds with fresher water, making the brewing process faster. The water is manually poured in an all-in-one stream instead of the showerhead-like contraption typically found in your auto-drip coffee maker.
(1) WebMD LLC. https://www.webmd.com/vitamins-supplements/ingredientmono-1266-caffeic%20acid.aspx?activeingredientid=1266&activeingredientname=caffeic%20acid
(2) ISIC the institute for scientific information on coffee. https://coffeeandhealth.org/all-about-coffee/compounds-in-coffee/
(3) Science of Cooking. https://www.scienceofcooking.com/maillard_reaction.htm
(4) Wikipedia. https://en.wikipedia.org/wiki/Furan-2-ylmethanethiol
(5) ccsenet. https://www.ccsenet.org/journal/index.php/jfr/article/viewFile/41001/23148
(6) ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0963996997000021
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