The New Coffee Brewing Chart: What Changed and Why It Matters

What does it take to brew a truly excellent cup of filter coffee? Choosing fresh, high-quality beans and clean water is a given, but the brewing method itself plays a central role.

For generations, coffee experts and enthusiasts have relied on the Coffee Brewing Control Chart (BCC) as a benchmark for brewing standards.

Developed in 1957 by Ernest E. Lockhart at the Coffee Brewing Institute, the BCC became a legendary reference in the coffee world. Its nine-square grid, resembling a tic-tac-toe board, lets users assess whether their brew is weak, strong, or—in the central square—ideally balanced. The Specialty Coffee Association (SCA) has incorporated it into its teaching since the 1980s, and much of its core coffee knowledge is built upon it.

But coffee science has advanced considerably since the 1950s. A research team at the UC Davis Coffee Center, with support from the SCA and funding from Breville, set out to bring Lockhart’s work into the 21st century. Their effort resulted in the Sensory and Consumer Brewing Control Chart, which merges contemporary coffee science with consumer research and a more approachable design.

The update has been embraced by many in the industry. But what did it take to modernize Lockhart’s classic chart for a new era?

A Historical Perspective

Lockhart, a biochemist, served as the first director of the Coffee Brewing Institute (CBI). Founded in the early 1950s by the National Coffee Association and the Pan American Coffee Bureau, the CBI aimed to ground the emerging coffee industry in rigorous science.

As Emma Bladyka noted in The Specialty Coffee Chronicle, “much of the work conducted by the CBI was towards determining the optimal methodology to brew good coffee … This focus on the consumer led the Institute to realize that the majority of complaints around coffee were the direct result of improper brewing methods.”

Lockhart published his findings in 1957 in a paper titled “The Soluble Solids in Beverage Coffee as an Index to Cup Quality.” That paper introduced the BCC, which employed total dissolved solids (TDS) and extraction yield to help users evaluate brew quality. TDS refers to the amount of soluble material extracted from the coffee that ends up in the cup, while extraction yield is the percentage of coffee grounds that dissolve during brewing.

An early version of Lockhart’s chart.

In essence, Lockhart reduced coffee brewing to a simple principle: the quality of a cup could be quantified by measuring how much of the ground coffee had dissolved into the liquid. His conclusions became a vital reference for the coffee industry.

“This chart, and the paper that explained it, is really the foundation of all of our modern thinking of how coffee extraction works,” says Peter Giuliano, executive director of the Coffee Science Foundation and chief research officer of the SCA.

Giuliano describes Lockhart’s research as a major leap forward in coffee science, influencing the entire field. “Lockhart’s genius was to realize that measuring dissolved solids in coffee could serve as an indicator—or ‘index’—to coffee quality,” Giuliano says. “That insight became a tool that could use physical measurement of total dissolved solids to help coffee professionals recognize well-brewed coffee.” Lockhart identified the ideal range for filter coffee as 18–22% extraction and 1.15–1.35% TDS. Measurements outside this range would yield under- or over-extracted—and thus unpleasant—coffee.

This chart has underpinned our understanding of coffee brewing, but after more than six decades, it was evident that an update was needed. For starters, coffee science had progressed significantly since the original chart’s publication. Lockhart relied on 1950s tools such as hydrometers (which measure liquid density) and mercury thermometers, whereas today’s instruments can perform the same tasks more quickly and accurately.

Together with advances in chemical analysis and sensory science, this made it possible to retest Lockhart’s conclusions and assess their accuracy. “To our delight, we discovered that not only was Lockhart’s theory of TDS being a good indicator of coffee’s flavor correct, it was even more interesting than we anticipated,” Giuliano says.

The Coffee Science Foundation partnered with the UC Davis Coffee Center to update the BCC, a project that yielded three peer-reviewed papers over seven years. The work culminated in a study published in the Journal of Food Science and an entirely new Sensory and Consumer Brewing Control Chart, which the authors hope “can be used by brewers of drip coffee to design coffees with specific sensory profiles and match the preferences of different consumer types.”

Modernizing the Classic

The UC Davis researchers began developing the new chart in 2017. While the process was relatively straightforward, it was also labor-intensive, says Dr. William Ristenpart, founding director of the UC Davis Coffee Center and one of the authors of the latest study.

Lockhart’s original chart used only a few simple tasting notes, Ristenpart explains, whereas modern resources like the World Coffee Research’s tasting lexicon and the Coffee Taster’s Flavor Wheel list over 100 possible flavor attributes in black coffee. To make the new chart as robust and useful as possible, Ristenpart and his colleagues aimed to collect extensive sensory data. “The experimental design was, in one sense, simple: Let’s take the same coffee and brew it to different extraction yields and different TDS’s, and then taste the heck out of it,” Ristenpart says. “It’s easy to say, but it was also very laborious.”

A simplified version of the new Sensory Brewing Control Chart.

To gather that data, the researchers assembled small panels of coffee tasters—each with 12 volunteers—who then underwent a calibration process lasting several weeks. Anyone who has tried to reach consensus among coffee professionals on what “acidic” or “bitter” precisely means knows how challenging calibration can be. (Ristenpart recalls having the panel agree on the smell of “rubber” by sniffing a rubber band.)

The researchers also conducted consumer preference tests, brewing coffee in various styles for a group of mostly UC Davis college students to determine which they preferred. The outcome closely mirrored Lockhart’s findings from decades earlier, with the average person’s preferences falling in the middle of the chart. However, Ristenpart notes this is slightly misleading: “It’s more accurate to say that it was the coffee that displeased the least people.”

This consumer preference data—which Ristenpart acknowledges is skewed toward a younger, North American demographic—was combined with the researchers’ technical and sensory data and condensed into the new charts.

Unlike Lockhart, the researchers produced four chart versions: the first displays the main sensory attributes of black drip coffee; the second visualizes the consumer preference research; these were then combined into a third chart that overlays consumer data onto the sensory attributes. The final chart is a streamlined version of the third, with a layout that in many ways echoes Lockhart’s original.

In the study, the authors describe the combined Sensory and Consumer Brewing Control Chart as “reflecting the integration and culmination of our comprehensive sensory and consumer research on the effects of brewing variables on the sensory quality and consumer acceptance of drip brew coffee.”

In the streamlined chart, the left vertical axis represents TDS, the bottom horizontal axis shows extraction yield, and the right vertical and top horizontal axes indicate the brew ratio with diagonal lines extending from each number. It includes fewer sensory descriptors than the combined chart but still marks the “ideal” zone in reference to Lockhart’s original.

Brewing Coffee Today

Most hobbyists—and even many coffee professionals—won’t have a TDS meter or refractometer at home to test their morning coffee against the chart. However, Ristenpart says that using a scale and comparing your coffee-to-water ratio to the graph, while adjusting grind size and brew time, will give you a good idea of what flavors to expect.

For example: Two brews, one with fine-ground coffee and one with coarse-ground coffee, will brew at different speeds and have higher and lower TDS. Users can then consult the chart and, hopefully, match the sensory descriptors to what they have brewed—sweet in the bottom left, bitter in the top right. “You won’t know exactly where on the chart because you don’t have a way of measuring TDS, but one’s going to be down to the lower left and one’s going to be upper right,” Ristenpart says.

For Giuliano, the updated chart reflects what Lockhart understood all along: that TDS and extraction percentages can reliably predict specific qualities—such as acidity, sweetness, and bitterness—when brewing coffee. This is, he says, “a powerful tool for professional and amateur coffee brewers alike.”

Ristenpart notes that, using the chart, it is even possible to accentuate certain flavors and make a single coffee taste markedly different depending on how it is brewed. “You could take the same pile of coffee beans and then, depending on how you grind them and how you extract them, get them to different corners of the Coffee Brewing Control Chart, which will make those same coffee beans taste differently.”

Even though the research affirms many of Lockhart’s original findings, Giuliano points out one major difference. Despite Lockhart’s original assertion that there was one ideal brewing zone, coffee consumers have a wide and diverse set of preferences. “‘Good coffee’ is not a singular thing,” he says, “but can mean different things to different consumer groups.”