By Michael Haft and Harrison Suarez
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.
This post is adapted from Michael Haft and Harrison Suarez’s Perfect Coffee at Home.
This article available online at:http://www.theatlantic.com/health/archive/2013/08/how-to-make-perfect-coffee/278944/