The best part of waking up is of course the hot soy juice in the cup.But, as Kate “Chemist” Dr. Biberdorf explains in her new book This is the elementIf you want to always enjoy the best cup of coffee you can make—the perfect coffee is not too bitter—a bit of math is necessary. It’s not just coffee. Biberdorf takes the reader through the ordinary moments of daily life, showing how incredible they are in fact-if you stop to study the chemical reactions behind them.
From This is the element Kate Biberdorf, Copyright © 2021 Kate Biberdorf. Published by Park Row Books.
Coffee and tea are more effective sources of caffeine than soda. In a cup of coffee, you may consume about 100 mg of caffeine, but if you use the right coffee beans and techniques, your intake may be as high as 175 mg. If you never thought about it, the whole process of making coffee beans (and the coffee itself) is very fascinating. For example, espresso machines and percolators get the most caffeine from lighter roasted coffee beans, but the drip method is the best way to get the most trimethylxanthine from darker coffee beans. However, generally speaking, light roast and dark roast coffee usually have the same relative number of caffeine molecules in each cup of coffee (excluding espresso).
Let’s look at the baking process to determine why this is the case. When the beans are initially heated, they absorb energy in what we call an endothermic process. However, at approximately 175°C (347°F), the process will suddenly release heat. This means that the coffee beans absorb so much heat that they now radiate the heat back into the roaster’s atmosphere. When this happens, you must adjust the settings on the device to avoid over-roasting the coffee beans (which can sometimes cause the coffee to burn). Some roasters even switch coffee beans between endothermic and exothermic reactions several times to obtain different flavors.
Over time, the roasted coffee beans will slowly change from green to yellow, and then to various shades of brown. We refer to the dark color of coffee beans as “roasting”, in which coffee beans with a darker roasting degree are much darker than those with a lighter roasting degree (surprise, surprise). Their color comes from the temperature at which they are baked. Lighter coffee beans are heated to about 200°C (392°F), while dark roasted coffee beans are heated to about 225-245°C (437-473°F).
But just when the coffee beans started, because there was no better word, the coffee beans experienced their first “cracking” before being lightly roasted. This is a sound process that occurs at 196°C (385°F). In this process, the beans absorb heat and double in size. But because water molecules evaporate from the beans at high temperatures, their mass is actually reduced by about 15%.
After the first burst, the coffee beans are very dry and can no longer absorb heat easily. Instead, all the heat is now used to caramelize the sugar outside the coffee beans. This means that heat is used to break the bonds in sucrose (sugar) into smaller (more fragrant) molecules. The lightest roasts—such as cinnamon roasts and New England roasts—are heated to the first crack before being removed from the coffee roaster.
A second crack will occur during the baking process, but the temperature is much higher. At 224°C (435°F), the coffee beans lose their structural integrity and the coffee beans themselves begin to collapse. When this happens, you can usually hear a second “pop” sound. Dark roasts are usually classified according to any coffee beans that have been heated for a second crack, such as French and Italian roasts. Generally speaking, due to the higher temperature, darker beans tend to have more sugar caramelized, while lighter beans have less caramelization. The flavor changes caused by these methods are crazy, but it does not really affect their reaction in the body-only the taste.
Once you have purchased perfectly roasted coffee beans, you can do the rest of the chemical work at home. Using a cheap coffee grinder, you can grind coffee beans into many different sizes, which will definitely affect the taste of your morning coffee. The small and fine grind has a large surface area, which means that caffeine (and other flavors) can be easily extracted from micro coffee beans. However, this usually results in too much caffeine being extracted, which gives the coffee a bitter taste.
On the other hand, coffee beans can be coarsely ground. In this case, the degree of exposure inside the coffee beans is different from that of finely ground coffee beans. The resulting coffee usually tastes sour—sometimes even a bit salty. However, if you combine the correct size of coffee grounds with the proper brewing method, you can make the best coffee in the world.
The easiest (and easiest way) to brew coffee is to add extremely hot water to the coarse coffee grounds. After they have been soaked in water for a few minutes, the liquid can be poured out of the container. This process is called decocting, which uses hot water to dissolve the molecules in the coffee beans. Most current coffee brewing methods use some form of decoction, which allows us to drink a cup of hot coffee instead of chewing some roasted beans. However, because this method does not include a filtration process, this version of coffee-affectionately called denim coffee-is prone to floating coffee beans. Therefore, it is usually not the preferred brewing method.
By the way, have you noticed that I’m avoiding the word boilingIf you want to make half a cup of decent coffee, hot water should never actually boil. In contrast, the ideal temperature of water is about 96°C (205°F), which is slightly lower than the boiling point (100°C, 212°F). At 96°C, the molecules that provide coffee aroma begin to dissolve. Unfortunately, when the water temperature rises by only 4 degrees, the molecules that make the coffee have a bitter taste will also dissolve. This is why coffee fans and baristas are so obsessed with their water temperature. In my house, we even use an electric kettle so that we can choose the water temperature we want.
Depending on how strong you like the coffee taste, you may prefer French press or other steeping methods. Like denim coffee, this technique also steeps coffee grounds in hot water, but these coffee grounds are smaller (coarse and extra-coarse). After a few minutes, use the plunger to push all the ground to the bottom of the device. The remaining liquid above the ground is now very clear and delicious. Since this method uses coarse coffee grounds, more molecules can be dissolved in the coffee solution, giving us a stronger flavor (compared to denim coffee).
Another technique: When hot water drops on coffee grounds, the water absorbs aromatic molecules before dripping into the coffee cup. This process is appropriately called drip irrigation and can be done manually or using high-tech machines (such as coffee filters). But sometimes this technique is used with cold water, which means that the fragrant aromatic molecules (the molecules that give your coffee a unique smell) cannot be dissolved in the water. The result is called Dutch ice coffee, which ironically is a beverage favored in Japan and takes about two hours to prepare.
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