How To Make The Best Coffee, According To Science

Thanks to Brilliant for supporting this SciShow List Show! As a SciShow viewer, you can continue developing your STEM skills with a 30-day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. If you're a

coffee

drinker, you've probably heard many rules about how to brew the perfect cup. Some people say that iced

coffee

is an abomination, or that you need to have the

best

Italian machine to

make

a halfway decent coffee. It is a little difficult to separate reality from the coffee myth. Fortunately, there is a wealth of research that can help. Crafting a beautiful cup of liquid gold may be an art form, but it is also very much a

science

.

And we at SciShow are here to tell you about all that rich, balanced and sometimes crazy research and show you how to brew the perfect coffee. It all starts with the coffee bean. What is the first point to debunk. Coffee beans are not beans at all! Sure, they may look bean-shaped, but beans are the seeds of legumes and coffee is not a legume, so those little nuggets are just regular seeds. But since almost all English-speaking people call them coffee beans, we'll stick with that in this video. Ok, if you're like me, you spend too much time browsing the supermarket shelves only to end up buying what's on sale.

After all, no one can tell the difference in those mixes, right? Well not so much. The two most widely used coffee plants, Arabica and Robusta, have considerably different amounts of the four main compounds that give coffee its characteristic flavors. First you have the alkaloids. These are compounds that have at least one nitrogen group and most have a ring structure. The two main alkaloids in coffee are caffeine and trigonelline, and both contribute to the bitter taste of coffee. Some studies have found that unroasted robusta beans have about twice the caffeine as arabica beans, but only about two-thirds the trigonelline, which overall would

make

robusta a more bitter bean.

The second main group of compounds in coffee are acids, particularly quinic and caffeic acids and chlorogenic acid, which is a combination of the two. And since it's acidic in its name, you can bet that these compounds give coffee its astringent or acidic flavor. Robusta has on average between 1.5 and two times more chlorogenic acid than Arabica, so in addition to being more bitter, it is also a little more astringent. Then there's sucrose or sugar, which unsurprisingly gives coffee its sweet notes, but also breaks down during roasting into sweeter tasting compounds. One reaction in particular, called the Maillard reaction, occurs when amino acids and sugars combine and give coffee its golden color and flavor.

Raw arabica beans have more sucrose than robusta beans, which gives it caramelized, fruity or fermented aromas when broken down. Finally there are furans, which give roasted coffee most of its flavor and in particular those malty or sweet notes. They form when carbohydrates or unsaturated fatty acids are broken down during roasting, and there are more of them in roasted arabica than in roasted robusta, giving arabica beans sweet, nutty flavors. So choosing the perfect bean for the flavor profile you want in your final cup is pretty vital, even if you're not thinking about furans or acids while you're in the coffee aisle.

Okay, but maybe you're less concerned about flavor notes and aromas, and more interested in getting the maximum amount of caffeine as quickly as possible. You have a deadline! So, while you're frantically Googling how to get as much caffeine into your system as possible, you may have read that lighter roasts contain more caffeine than darker roasts. I'm sorry to tell you that this is a bit of a myth and here's why. See, a lighter roast of coffee literally means that it was roasted for less time or at lower temperatures. And while some compounds in those beans are broken down during roasting, caffeine is not one of them.

But although caffeine is not broken down, it can be released during roasting when the pores of the coffee beans close, gas builds up inside, and the beans eventually open. However, different studies have evaluated the level of caffeine depending on the roast level and most have not found any significant difference. But there may still be a little truth to this myth, depending on how you measure the beans for that cup of coffee. You see, beans lose mass as they roast, but they also increase in volume. That means darker roasts become lighter and take up more space than lightly roasted ones.

So if you compare a serving of light versus dark roast, you're probably measuring fewer beans and therefore potentially less caffeine. Despite all that, the differences between a dark roast and a light roast are probably so small that you wouldn't notice them when drinking them. Alright, you've collected the beans and ground them, and now it's time to prepare them. In scientific terms, many of the properties of coffee, such as smell, flavor and texture, come down to chemical and physical kinetics; how chemicals react and how things move. You may not immediately think of coffee as something that moves, but brewing coffee involves hot water moving over or around the coffee grounds, either forced by pressure or thanks to gravity.

There are a couple of ways this can happen. There are brewing methods, such as pour-over, where water flows over coffee grounds and those grounds are soaked in water, usually hot, for a short period of time before being filtered, all with the help of gravity to make pass the infusion. Infusion methods typically result in a smoother, less harsh cup of coffee and are suitable for bringing out lighter, fruitier flavors. Decoction methods, such as percolator coffee, boil ground coffee in hot water before condensing the coffee vapors back into a liquid. Those high temperatures of a decoction method mean that the coffee compounds are absorbed very quickly, but there also isn't much contact time between the ground coffee and the water, so you end up losing some flavor and ending up with a very strong flavor. cup of rather bitter coffee.

Then there are pressure methods, such as espresso, in which hot water is forced onto highly compacted soil. Yes, espresso is a method of brewing coffee, not a specific type of bean! Although you may see bags on store shelves labeled "espresso," it's not actually espresso unless it's brewed to make, well, espresso. The combination of slightly different particle sizes in ground coffee means that those ground beans clump together when you press them before feeding them into the machine. And that makes the mixture better resist pressure during preparation. Then, if there is good pressure resistance, the energy of the hot water is transferred to the coffee grinding block, extracting more oils with the water and giving the deep flavor and creamy texture of espresso.

That is why it is very important to choose the method to prepare coffee! If you really want to dial in particular coffee flavors, you may also want to take a close look at your water source. Hard water is full of positive ions, such as magnesium and calcium ions, which can pick up tasty compounds. And interestingly, those ions could make your final drink that much better. See, each of those molecules that give coffee its flavor, whether it's caffeine or one of the acids, has some negatively charged electrons around it. The positively charged ions in hard water are attracted to these negative parts of the coffee compounds, which helps draw them into the water.

In a 2014 study, researchers looked at how well magnesium, sodium, and calcium bind to coffee compounds such as caffeine, malic, citric, quinic, and chlorogenic acids, as well as a clove-flavored compound. spicy called eugenol. They found that magnesium bound most strongly and closely to all compounds, followed by calcium. In reality, the sodium did not attach to any of the compounds any more than the water molecules. So, at least

according

to this study, opt for magnesium-rich water if you want to get the most flavor out of your beans. But there is a problem. You should also make sure the water contains enough baking soda to keep the acidic components under control.

So yeah, that coffee shop bro who brags about how they filter their water via triple osmosis could be doing more to make even less tasty coffee. So now that he's picked out his bag of beans at the store, he might be staring at that giant coffee grinder, trying to figure out which setting to choose. Or maybe you took an espresso class and were told to take a lot of beans and grind them very fine. That advice makes sense, since there's plenty of surface area for the water to extract all those delicious coffee compounds. But pulverizing coffee into literal powder may not be the way to go.

At least

according

to the math. The Darcy-Forchheimer Law, named after the engineers who developed it, was originally designed to explain how water flows through a column of sand. But it works just as well for coffee! Predict how water will flow over those coffee grounds, depending on things like the gradient the water moves down and the area it moves through. And that can tell you something about how strong or flavorful the drink may be. If the particles are too fine, water cannot pass through and the coffee goes a long time without having its juice sucked out, making it bitter or over-extracted.

However, if it is too coarse, the hot water will simply flow over the ground coffee, extracting little of the flavors and leaving you with bitter coffee. In a 2020 study, researchers created and tested a mathematical model, based in part on the Darcy-Forchheimer law, to achieve the perfect espresso setting. When they ground the beans too fine, they ended up with uneven regions of pressure building up in that little mound of coffee. That meant that only some of the coffee was properly extracted and they ended up with coffees that were different from cup to cup. So, unlike typical barista tradition, they discovered that using less coffee (15 grams instead of the usual 20) and grinding it more coarsely and consistently gave them much better-tasting brews.

And like

science

in general, reproducibility is what you're looking for when it comes to your morning cuppa. Plus, by using fewer beans, you'll end up with more cups of coffee in your bag and less waste. Win, win! Now, we all know that grumpy person who insists on ordering their latte extra hot. Or the purist who says iced coffee is an abomination to the art of coffee. Although neither is 100% correct, temperature plays a pretty important role in the flavor of the final cup. The National Coffee Association recommends a temperature between 90 and 96 degrees Celsius, or 195 and 205 Fahrenheit, just below boiling temperature.

This is because the temperature of the water dictates how quickly all those flavor compounds leach out of the grind. You see, as the temperature increases, the water molecules gain energy and interact more with the coffee grounds. More interaction means more mining! Now, some coffee flavor compounds that are actually water-soluble are removed from coffee quickly, regardless of temperature. These include quinic, malic and citric acids. But there are also compounds that dissolve differently in water at different temperatures. These are mainly the compounds that give coffee its bitter taste, like the alkaloids we talked about earlier. So, with hotter water, more bitter compounds are leached.

Very hot water can also release other compounds such as pyrazines, which give an earthy or burnt taste. That's probably why people often report that coffee brewed at higher temperatures can taste quite bitter. But scalded coffee is also described as acidic, which doesn't immediately make sense since acidic compounds come out regardless of temperature. Coffee scientists, who basically have my dream job, believe that bitter and acidic compounds have an additive effect. So if more bitter compounds like caffeine get into the water at higher temperatures, this makes the acidic compounds taste more sour. Now you might be wondering about cold beer.

In cold brewing, it's time that does all the work, not temperature. Cold water slowly sucks those flavor compounds out of the soil. And some compounds, including chlorogenic acids and trigonelline, are filtered out much more slowly. So depending on how long you steep the coffee, cold brew is generally sweeter and less acidic. And now that you have your coffee maker, your beans, and a ton of scientific knowledge, you're ready to make your coffee. Having said all that, the perfect cup of coffee is the one thatlike. If you're looking to up your brewing game, don't hesitate to take what you've learned here into the kitchen.

But if your coffee hits the mark, there's no science that can tell you you're wrong! And this one is pretty good. I'm going to take a refill! But first, I must thank Brilliant for supporting this List Show. Brilliant is an online learning platform with thousands of interactive lessons in math, science, and computer science. Like their Measurement course, which covers angles, length, area, surface and volume. And the latter can come in handy when you're trying to figure out how much coffee will fit in your favorite mug. The brilliant courses are even available offline via their iOS and Android app.

So if you're at one of those coffee shops that don't share wifi, you'll still be able to keep learning. You can check it out at Brilliant.org/SciShow or at the link in the description below. That link also gives you a 30-day free trial and 20% off an annual Brilliant premium subscription. Thanks for watching this SciShow video!