How to Make Perfect Coffee
The science of what makes coffee great
Coffee has become recognized as a human necessity. It is no longer a luxury or an indulgence; it is a corollary of human energy and human efficiency.
It was November 23, 2010. We were in Surf City, North Carolina, getting ready to fortify ourselves before another grueling day. As the thin, black liquid oozed into the stained carafe, we stood bleary-eyed.
We were roommates, Marine infantry officers, perpetually sleep-deprived from the training, the planning, the preparations for war. Back then coffee was little more than a bitter, caffeine-delivery system. It was just what we needed to stay awake.
We were missing so much.
Fast-forward a few years. We've hung up our uniforms, we're in the kitchen, and we're making coffee. Great coffee. The kind that reminds you first thing in the morning of everything else you appreciate in life. It's about the art, the ritual, and the moments shared across a table.
And yet, if you're like us, no one ever taught you how to make coffee properly. Or how to appreciate it. When you stop in at your local coffee shop, everything is hidden away behind the counter, too far removed for you to understand. That was us not too long ago. But through trial and error—and an absurd amount of mistakes—we've managed to learn. It's a shame to waste these moments on bad coffee, and if you're going to drink it every day, or if you're going to serve it to other people, it may as well be good, right?
Actually, it should be better than good. It should be perfect.
What is Good Coffee?
To understand good coffee, we have to start with how the coffee world measures its brews. After all, if you're trying categorize your coffee, it helps if you have a benchmark.
Measuring the quality of coffee goes back to the 1950s, when MIT chemistry professor E. E. Lockhart conducted a series of surveys to determine American preferences. Basically, he surveyed a lot of coffee drinkers and asked them what they liked.
Lockhart published his findings in the form of the Coffee Brewing Control Chart, a graphical representation of what Americans at the time considered to be the best coffee. In the years since, the Specialty Coffee Association of America (SCAA) has confirmed that American tastes haven't changed all that much. Perfection, at least to Americans, is a coffee that falls in the range of 18 to 22 percent Extraction with a brew strength between 1.15 and 1.35 percent Total Dissolved Solids.
Confused by the jargon? Don't be.
The Percentage Extraction is the amount of coffee particles extracted from the original dry grounds. The Percentage of Total Dissolved Solids is the percentage of coffee solids actually in your cup of coffee (commonly known as "brew strength"). When you correlate these, the result is a Coffee Brewing Control Chart, with a target area in the center that highlights the optimal brew strength and extraction percentage.
When you're brewing coffee, the goal is to get into that center square of perfection. Everyone seems to advocate their own sort of mystical process for achieving the right extraction, but we're here to tell you it's not that crazy.
Instead, the key is to start with the Golden Ratio of 17.42 units of water to 1 unit of coffee. The ratio will get you into that optimal zone, plus it is unit-less, which means you can use grams, ounces, pounds, stones, even tons if that's your thing. So if you're hoping for a 20 percent extraction against 1.28 percent Total Dissolved Solids, you can start with 30 grams of dry coffee grounds, 523 grams of water, and then adjust from there.
Meanwhile, a common mistake is to mix up Percentage Extraction with Total Dissolved Solids. It's important to understand the difference.
Strength refers to the solids that have dissolved in your coffee. Percentage Extraction refers to the amount that you removed from the dry grounds. The point is that strong coffee has almost nothing to do with bitterness, caffeine content, or the roast profile, and everything to do with the ratio of coffee to water in your cup.
The great innovation in measuring all this stuff came about in 2008, when a company called Voice Systems Technology decided to use a refractometer—a device that bounces light waves off of particles—in conjunction with a program they developed called ExtractMojo.
The device allows you to get an accurate reading on Total Dissolved Solids and then compare your brews to the Coffee Brewing Control Chart. In this way, you can refine your results based on science as well as taste.
Some purists chafe against the idea of introducing a device like this to measure the quality of a cup of coffee. As former Marines, it reminds us of a similar debate on the topic of gun control.
Are guns the problem, or is it how people use them?
Are refractometers the problem, or is it how people use them?
These are hotly debated issues and for good reason. But both are tools, and just like any other, they can be misused.
We prefer to think of it like castle doctrine; use your refractometer in the privacy of your own home.
The Principles of How to Make Coffee
Once you understand what good coffee actually is, and once you understand how people measure it, it's much easier to learn how to make coffee.
The six fundamental principles are:
- Buy good coffee beans: They should be whole beans, sustainably farmed, and roasted within the past few weeks. Plus, if you want to take part in the "third wave" coffee renaissance currently sweeping America, they should be a lighter roast so you can actually taste the flavors—the terroir—of the coffee. With darker roasts, you're missing out. We know it's a weird analogy, but a dark roast is just like taking a nice steak and charring it beyond recognition.
- Grind your coffee just before brewing: Roasted coffee is very delicate and perishable. Coffee has many more flavor compounds than wine, but those compounds deteriorate quickly when exposed to oxygen. Grinding your coffee just before you brew it keeps those compounds intact, and it's the number one thing you can do to improve your coffee at home.
- Store your coffee properly: Beans which you aren't using immediately should be kept in an airtight container and away from sunlight. A major point of debate in the coffee world is whether to freeze or not freeze your coffee. We fall somewhere in between. If it's going to be more than two weeks before brewing, we freeze our coffee. Otherwise, we avoid it.
- Use the right proportion of coffee to water: A major error people make is not using enough coffee. We empathize—it almost seems wasteful to add that extra scoop. But the Golden Ratio we mentioned earlier really is a great starting point and the simplest way to get into that perfect zone.
- Focus on technique: It's beyond the scope of this guide to go through step-by-step instructions for every method, but underlying all of them is the fact that brewing great coffee is about precision and consistency. Each brewing method has its own particular techniques, but by doing the same thing over and over you fix your mistakes and improve incrementally.
- Use quality tools: You're going to get better results from high quality tools than you will with junk from the bargain bin. Yes, it's more of an upfront investment, but in the long run it's worth it. Good tools last longer and make the entire brewing process much easier.
Classic Methods and Fine Tuning
With these principles in mind, pick a preparation method. These lie along a spectrum: Body on one end, flavor clarity on the other, with variations in between. The balance between body and flavor clarity is determined by the parts of the coffee bean that make it into your cup.
Unfortunately, way back at the beginning of our journey when this was all foreign to us, no one ever explained why a French press had so much body or why a pour over had such articulate flavors. It was all shrouded in secrecy. So we took these mysteries at face value and filed our questions away.
Eventually, we discovered that the answer lay in chemistry, which divides the world into soluble and insoluble compounds. Soluble particles are extracted from the coffee grounds and contribute to flavor and aroma, while insoluble particles primarily contribute to the body of coffee. Since a roasted coffee bean is made up of both types of particles, the way you balance those during the extraction process determines the resulting character of your cup.
Do you prefer a richer, grittier cup of coffee? Try a French press. Looking for a cleaner cup that can highlight citrus notes from South America or berry flavors from Africa? Check out the pour over. Everyone's preferences vary, but once you select a method, you can further fine tune your coffee by adjusting these variables:
- The grind size of your coffee beans: Grind size affects the extraction rate because it affects surface area. Beans that are coarsely ground have less surface area than the same amount of finely ground beans, making it more difficult for the water to penetrate and extract the coffee solids. A uniform grind size means that the extraction rate of the oils and acids in the coffee will be consistent. You won't have large pieces that under-extract and small pieces that over-extract. It's for this reason that you'll often hear coffee experts exhorting people to invest in a good burr grinder. And guess what? They're right.
- The temperature of your water: Temperature affects extraction rate because solids dissolve more quickly at higher temperatures. Temperature also affects flavor because it determines which solids get dissolved. Using water that's too hot will lead to sour coffee since it releases unpleasant acids from the coffee beans. For this reason, we recommend brewing with water between 195 and 202 degrees. And remember, measure the water actually in the coffee and not just what you're pouring. There's often a difference.
- The amount you agitate your coffee grounds during brewing: You can further manipulate the brewing process by agitating the coffee grounds as the water passes through them. Agitation works because it accelerates the spread of dissolved coffee solids throughout the water, exposing the coffee grounds to fresher water more quickly. But agitation also has the effect of cooling the water, which we know can affect the process. In the end, it's just one of those things that you learn through trial and error.
- The ratio of water to coffee: Strange how it keeps coming back to this, right? The key difference here is that when you're fine tuning, you aren't sticking strictly to the Golden Ratio. Instead, you're adjusting to taste. To make adjustments more easily, invest in a scale. You can be more precise by using weight—instead of volume—to measure your coffee and water.
One final point. As any good barista will tell you, make sure to adjust only one variable at a time so you can accurately track results. Changing two variables at a time confounds the outcome, and you won't know whether it was because you changed variable X or variable Y.
This Isn't Rocket Science
For all our talk of chemistry, particles, molecules, and extraction percentages, brewing great coffee is much less about science and much more about art. Once you learn the principles that underly the brewing process, you can develop a routine which suits you perfectly.
And that's the beauty of coffee. When we first started our journey, we were embarrassingly ignorant about the most basic aspects. The choices, the culture, the equipment—it was all so overwhelming that we had no clue where to begin.
But pretty quickly we found ourselves climbing the coffee learning curve. Learning to brew great coffee didn't have to take forever. It was a hobby that you could pick up on a Saturday morning and feel good about.
As we explored, there were good moments and bad ones, and stretches where it felt as if we couldn't do anything right. We wasted a ton of time. We destroyed a lot of coffee. And although we read as much as we could, there were occasions when we were as stubborn as we were ignorant, days when we had to learn from our own mistakes because we didn't understand or didn't listen to what we had been taught.
But each mistake also meant progress. We had discovered one more thing which didn't work. There was always something new to try, and in this haphazard fashion, we grew.
For us, this was the enduring lesson, that learning is continuous, that there is always room to improve, to explore, and to innovate.
And while much of the knowledge already existed, and although the modern exploration of coffee has been going on for at least a hundred years, through this journey, it was our turn to participate.
And now it's yours.
This post is adapted from Michael Haft and Harrison Suarez's Perfect Coffee at Home.