Read the full academic paper in the Journal of Food Science

Beverage color significantly affects perceived sensory quality and consumer preference. Although the color of coffee beans is well known to vary strongly with roast level, little work has examined how roast level and brewing conditions affect the color of the final beverage. Here, we report that the color of full immersion brewed coffee is significantly affected by both roast level and brewing temperature. Coffees from three different origins were each roasted to three different levels (light, medium, and dark) and then brewed at three different temperatures (4, 22, and 92°C). Each sample was brewed toward full extraction and then diluted to precisely 2% total dissolved solids so that differences in concentration would not confound color measurements. Absorbance spectra (UV-vis) and color tristimulus values (L*a*b*) were then collected and analyzed. We find that roast level had the strongest impact on brew color, and that brew temperature had a significant impact on color for light and medium roasts, with less impact on dark roasts. Qualitatively, the cold brewed coffees tended to be redder, while the hot brewed coffees were blacker. The results suggest that there is an opportunity to manipulate and brand brewed coffee color through judicious choices of roast level and brewing temperature.

Read the full article in the SCA Portal.

ANDREW COTTER considers the results of recent scientific publications focused on the impact of coffee’s brewing temperature on consumer preferences of brewed coffee.

Many of these variables—such as growth altitude, processing method, and roast level—can be controlled on a large scale by farmers and roasters in an effort to produce many bags of coffee that are nearly identical to one another. However, whole coffee beans in bags have not yet finished their process. Additional steps, such as grinding and brewing, are needed to make the final beverage that people will enjoy as their coffee. With these steps, a host of variables—that may influence the flavor of the brew and, in turn, how consumers like it—are in the hands of baristas and home brewers alike.

Read the full article in the SCA Portal.

Lead author Dr. MACKENZIE BATALI outlines findings from a recently published paper, “Titratable Acidity, Perceived Sourness, and Liking of Acidity in Drip Brewed Coffee,” that illuminate a key specialty coffee flavor attribute.

Beyond contributing either positively or negatively to the reception of the coffee, acidity is also mentioned as a component of other cupping score categories including flavor, balance, and defects; it likely contributes to uniformity and overall score as well.

Read the full academic paper in Critical Reviews in Food Science and Nutrition or access through an open-source data format on the Dryad Digital Repository

Coffee contains a variety of organic acids (OAs) and chlorogenic acids (CGAs) that contribute to overall sensory properties. Large variations in preparation and measurement methodology across the literature complicate interpretation of general trends. Here, we perform a systematic review and meta-analysis of the published literature to elucidate the concentrations of OAs and CGAs in both Coffea arabica (arabica) and Coffea canephora (robusta), for both green coffee and roasted coffee at multiple roast levels. A total of 129 publications were found to report acid concentration measurements, yielding 8,634 distinct data points. Analysis of the full data set reveals several trends. First, roasted robusta has considerably more acidic compounds than arabica with 2 to 5 times as much total OAs, and much larger amounts of formic and acetic acid. As for CGAs, in both arabica and robusta 5-CQA is the major component, and progressive roasting decreases the concentration of all CGAs. The total amount of CGA present was more dependent on roast level than the type of coffee (arabica vs. robusta). Overall, this meta-analysis suggests that the increases in certain OAs with roast level might play more of a role in the sensory profile of dark roast coffees than previously suspected.

Read the full academic paper in ACS Food Science and Technology

Acidity is a highly prized attribute in coffee, but there is little understanding of the brewing conditions under which acidity contributes favorable sensory attributes versus unfavorable sourness. Here, we examine the effect of titratable acidity and pH on the perception of sourness and consumer acceptance in drip brew coffee. Sour perception and acidity liking were assessed over a wide range of brew strengths and extraction yields at three different roast levels (light, medium, dark) and three different brewing temperatures (87 °C, 90 °C, and 93 °C). We find that perceived sour intensity correlates weakly with pH, but strongly with titratable acidity. Increases in titratable acidity also yielded increases in consumer perception of “too much acidity” and also impacted consumer liking and consumer preference segmentation with one cluster of consumers preferring more acidic coffee. Importantly, our data show that titratable acidity is linearly correlated with total dissolved solids (TDS) under all conditions studied, indicating that TDS is a good proxy for titratable acidity. The results presented here will provide the coffee industry with insight toward controlling perceived acidity or sourness, a key sensory attribute that substantially impacts consumer acceptance.

Read the full academic publication in Scientific Reports

The sensory qualities of brewed coffee are known to be strongly correlated with the total dissolved solids (TDS) and extraction yield (E) of the brew. Here, we derive a predictive model for the TDS and E of full immersion brewed coffee using a pseudo-equilibrium desorption approach. Assuming a single, species-averaged equilibrium constant 𝐾 yields theoretical predictions indicating that the TDS is approximately inversely proportional to the water/coffee mass brew ratio, while E is independent of the brew ratio. Our experimental results strongly accord with both theoretical predictions, and indicate that E is approximately 21% over a wide range of brew ratios. An analysis of the standard oven-drying method for measuring E indicates that it yields significant underestimates of the true value at equilibrium, due to retained brew within the spent moist grounds. We further demonstrate that 𝐾 is insensitive to grind size, roast level, and brew temperature over the range 80–99 °C. Taken together, our results indicate that full immersion brewing offers precise control over the TDS at equilibrium but little control over E, and that practitioners should pay careful attention to their brew ratio as the most important parameter for full-immersion brewing.

Read the full academic paper in Journal of Food Science

Brewing is the final and key step in the production of the coffee beverage. Extraction related metrics such as the total dissolved solids (TDS), percentage extraction yield (PE) of solutes, and brew temperature (BT) are widely believed to govern the flavor and corresponding consumer acceptance of the resulting brew, as summarized in the industry standard “Coffee Brewing Control Chart.” In this study, we investigated how the three factors of TDS, PE, and BT affected consumer acceptance of a medium roast, single‐origin coffee and whether consumer preference segmentation would be observed based on these variables. A cohort of 118 mostly college‐age, self‐reported consumers of black coffee tasted coffees that varied in BT, TDS, and PE. For each coffee, consumers rated overall acceptance on the 9‐point hedonic scale; the adequacy of serving temperature, flavor intensity, acidity, and mouthfeel using 5‐point just‐about‐right (JAR) scales; and described the flavor using a check‐all‐that‐apply list of 17 attributes. Cluster analysis revealed two consumer segments whose preferences varied most strongly with TDS. Response surface methodology relating liking to TDS and PE produced dome‐ and saddle‐shaped surfaces for the two segments, respectively. External preference mapping and penalty analysis indicated that overall flavor intensity as well as acidity heavily influenced the preferences of the two clusters. The Coffee Brewing Control Chart's “ideal” coffee should therefore be reconsidered to reflect consumer preference segmentation.

Read the full article on the SCA Portal.

Postdoctoral scholar SCOTT FROST, PhD candidate MACKENZIE BATALI, Professor JEAN-XAVIER GUINARD, and Professor WILLIAM D. RISTENPART share the results of sensory descriptive experiments at the UC Davis Coffee Center, revealing new trends in brewed coffee that suggest an updated brewing control chart.

Read the full academic paper in Scientific Reports

The brew temperature is widely considered a key parameter affecting the final quality of coffee, with a temperature near 93 °C often described as optimal. In particular, drip brewers that do not achieve a minimum brew temperature of 92 °C within a prescribed time period fail their certification. There is little empirical evidence in terms of rigorous sensory descriptive analysis or consumer preference testing, however, to support any particular range of brew temperatures. In this study, we drip-brewed coffee to specific brew strengths, as measured by total dissolved solids (TDS), and extraction yields, as measured by percent extraction (PE), spanning the range of the classic Coffee Brewing Control Chart. Three separate brew temperatures of 87 °C, 90 °C, or 93 °C were tested, adjusting the grind size and overall brew time as necessary to achieve the target TDS and PE. Although the TDS and PE both significantly affected the sensory profile of the coffee, surprisingly the brew temperature had no appreciable impact. We conclude that brew temperature should be considered as only one of several parameters that affect the extraction dynamics, and that ultimately the sensory profile is governed by differences in TDS and PE rather than the brew temperature, at least over the range of temperatures tested.

Read the full academic paper in Journal of Food Science

Drip brewed coffee is traditionally quantified in terms of its strength, also known as total dissolved solids (TDS), and its brewing yield, also known as percent extraction (PE). Early work in the 1950s yielded classifications of certain regimes of TDS and PE as “underdeveloped,” “bitter,” or “ideal,” with the modifiers “weak” or “strong” simply correlated with TDS. Although this standard is still widely used today, it omits a rich variety of sensory attributes perceptible in coffee. In this work, we used response surface methodology to evaluate the influence of TDS and PE on the sensory profile of drip brewed coffee. A representative wet-washed Arabica coffee was roasted to three different levels (light, medium, or dark), with each roast then brewed to nine target brews that varied systematically by TDS and PE. Descriptive analysis found that 21 of the 30 evaluated attributes differed significantly across the brews for one or more experimental factors, yielding linear or second-order response surfaces versus TDS and PE. Seven attributes exhibited a significant response surface for all three roast levels tested: burnt wood/ash flavor, citrus flavor, sourness, bitterness, sweetness, thickness, and flavor persistence. An additional seven attributes also showed a significant response surface fit across some but not all roasts. Importantly, sweetness exhibited an inverse correlation with TDS irrespective of roast, while dark chocolate flavor and blueberry flavor decreased with TDS for medium roast. These results provide new insight on how to optimize brewing conditions to achieve desired sensory profiles in drip brewed coffee.

Read the full academic paper in Journal of the Science of Food and Agriculture

The composition of drip brew coffee versus brewing time has been chemically characterized in previous studies, and it is known that the total dissolved solids (TDS) systematically decreases with each fraction during the brew. Little information exists regarding the corresponding sensory attributes versus time, however, and it is unclear how TDS correlates with flavor profile.

The results of the sensory analysis and the monosaccharide analysis suggest that perceptible sweetness in coffee is a consequence of masking effects and/or the presence of sweet‐associated aromas and flavors. The results further suggest that unique flavor profiles could be obtained from the same coffee grounds by judicious combinations of specific fractions. © 2020 Society of Chemical Industry

Read the full article on the SCA Portal.

Graduate student MACKENZIE BATALI, Professor CARLITO LEBRILLA, Professor JEAN-XAVIER GUINARD, and Professor WILLIAM D. RISTENPART share surprising results of “fractionation” experiments at UC Davis exploring the natural sweetness of black drip brew coffee in partnership with the SCA and Breville Corporation.

If you talk to aficionados of specialty coffee, however, you quickly learn that other sensory attributes are paramount. In fact, a word you are likely to hear from coffee experts, often uttered in reverential tones, is sweetness.

Typical consumers associate sweetness in coffee with the act of stirring in sugar or artificial sweetener, but that’s not what we’re talking about here. Rather, coffee experts have long known that black coffee, without any additives, can have perceptible sweetness. Considered by many to be the holy grail of specialty coffee, natural sweetness is a sublime pleasure for those who get to enjoy it in the cup. At the same time, however, natural sweetness can be maddening to those who need to make it happen. Anybody who sources, roasts, or brews coffee professionally knows that delivering natural sweetness in black coffee isn’t easy: sweetness is fleeting, fluctuating from lot to lot of beans or in response to minor differences in roast or brew conditions. This difficulty raises an important question: How do you maximize the natural sweetness in black coffee?

The Specialty Coffee Association (SCA) has announced the publication of the US Coffee Market Overview 2018. This report offers a large-scale understanding of coffee retail sales in the US and explores where people buy and consume their coffee.

Read the full academic paper in Journal of Food Science

In this work, discrimination tests, descriptive analysis, consumer tests, and total dissolved solids (TDS) were used to evaluate the effects of brew basket geometry on the sensory quality and consumer acceptance of drip brewed coffee. Semi‐conical and flat‐bottom brewing shapes were evaluated in conjunction with coffee roast and particle size. This research found that attributes showing significant interactions with brewing geometry were also key drivers of consumer liking/disliking. Overall consumer liking was analyzed by cluster analysis, which revealed four distinct preference clusters. For each cluster, a particular basket geometry and/or roast level showed lesser acceptance, further confirming the hypothesis that basket geometry affects the sensory quality of drip-brewed coffee.

Read the full article on the SCA Portal.

One of the most reliable ways of starting a passionate argument, at least in a room filled with coffee aficionados, is to ask a simple question: What is the best shape for a drip brew filter basket?