Sometimes an idea can change the world. Ernest Earl Lockhart had one of those ideas— one that changed the coffee world at least.

For food science nerds, Lockhart is a fascinating figure.

After completing a post-doc in Stockholm, Sweden, Lockhart joined a US expedition to Antarctica, where Mount Lockhart still bears his name. He then taught in the food science faculty of his alma mater, MIT, before leaving to become research director of the Coffee Brewing Institute.

The research Lockhart conducted at the Coffee Brewing Institute still sets the foundation of much of what we know about coffee brewing. At the center of Lockhart’s research: the coffee brewing control chart.

In retrospect, Lockhart’s idea was simple enough. He argued that brewed coffee’s quality is largely determined by the percentage of coffee extracted and the concentration of the finished beverage (TDS).

Roasted coffee is roughly 30 percent water-soluble. These soluble compounds include organic acids like citric acid and chemicals like caffeine.

Lockhart proposed that most coffee consumers prefer an extraction between 18 and 22 percent. Below this threshold, coffee was likely to taste sour or vegetal. Above, bitter and astringent. Similarly, at low concentrations, the coffee will taste weak and watery; at higher concentrations, intense and heavy.

Lockhart mapped the relationship between strength and extraction with a graph. Extraction, or solubles yield, is represented on the x-axis and strength, or solubles concentration, on the y-axis. The relationship between strength and extraction could be manipulated by changing the coffee-to-water ratio. In the center of the graph, the “gold cup” provides a target for coffee brewers to achieve.

Lockhart’s research proved seminal for Ted Lingle, who popularized the chart with his book The Coffee Brewing Handbook. Other coffee thought makers, like Scott Rao, have quibbled with Lockhart’s conclusions (Rao prefers a higher extraction percentage), but have agreed with the basic premise.

A New Coffee Brewing Control Chart

In 2023, the UC Davis Coffee Center published research that called aspects of Lockhart’s thesis into question. In a journal article entitled “A new Coffee Brewing Control Chart relating sensory properties and consumer liking to brew strength, extraction yield, and brew ratio”, Professors Jean-Xavier Gurnard and Scott Frost critiqued the original coffee brewing control chart for mixing descriptive language like “bitter” with hedonic language like “underdeveloped” (Curiously, the paper does not interact with the most recent version of the coffee brewing control chart, published in 2019 after the merger of the SCAA and SCAE, which avoids this error.)

More significantly, they propose that perceived sweetness in coffee is highest at lower strengths and extractions, rather than middle-of-the-chart extractions as previously taught.

The paper also challenges the notion that consumers prefer one optimal extraction. Instead, the researchers identify flavor profiles such as “fruity” or “black tea” that are most prominent at different parts of the chart (top left and bottom right, respectively). The researchers suggest that different consumer groups might enjoy different “ideals” and call for the chart to be revised in light of these findings.

Different philosophies

The different perspectives can be seen through a philosophical lens.

The grid is often identified as the symbol of modernism; straight lines arranged in a perpendicular binary. In this sense, Lockhart’s research betrayed the ideals of his time: we can use science to make the perfect cup of coffee.

But contemporary sensory science no longer speaks in ideals, only consumer preference groups. In a post-structuralist world, who’s to say what the best cup of coffee is?

If you like a fruit bomb flavor profile, why not updose to maximize that juicy acidity? These approaches to brewing coffee “outside of the box” have coincided with the rise of anaerobic and co-fermented coffees, which brew differently from conventional coffees and have atypical flavor profiles.

The Barista as Tastemaker

Taste, by definition, is subjective. Anyone who has worked as a barista knows that consumers have idiosyncratic taste preferences.

But I believe the barista plays a role in taste-making, and I don’t mean introducing customers to cool indie bands.

Allow me to share a personal anecdote.

I started drinking coffee as a college sophomore. Back then, my typical order was a caramel latte with extra syrup. I enjoyed this sickly-sweet beverage until a barista friend finally leveled with me. “You know, a caramel latte is pretty sweet as it is. You don’t need the extra syrup,” he said.

I was surprised to find he was right.

A few years later, I dropped the syrup altogether and started drinking black coffee and espresso. Fast forward a few more years, and I’m judging barista competitions and founding a company that designs and manufactures pour-over drippers.

The journey from enjoyer of sugary milk beverages to SCA Trainer is an unlikely narrative, and it might never have happened if a barista hadn’t been daring enough to tell me that I had bad taste.

I’m not advocating that we police customers’ orders or take away the sugar from condiment bars. (We tried that. It didn’t work.)

But I do think coffee professionals have an obligation to set a standard, execute it, and communicate why it’s important.

Sure, that peach note in an Ethiopia Yirgacheffe will pop if you use a stronger ratio, but what about the jasmine aromatics? What about the subtle black tea tannins? Maybe a trained sensory panel identifies coffee being “sweetest” at lower extractions, but does that mean it’s a better beverage?

The well-rounded beauty of a complex, balanced coffee is not immediately apparent to all consumers. It’s an acquired taste. To acquire the taste, one first has to experience it.

That’s not to say that good coffee is a monolith. I often tell my students, I want you to understand the rules so you can be free to break them.

We need a lodestar. A reference point. Dare I say, an ideal.

So, yes, I’m interested in consumer preference studies. I welcome the research coming out of the UC Davis Coffee Center. I think specialty coffee is a big enough tent to host different styles, aesthetics, and tastes.

But I’m still using the old Coffee Brewing Control Chart.