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Professors CARLOS CARPIO, PhD and LUIS SANDOVAL, PhD worked with BRENDA MAMANI, MSc to ask: what are the living wages in El Salvador and Honduras, and how would current total costs and profitability of coffee production be affected if farmworkers were paid living wages?

Read the full article in the Journal of the American Society for Horticultural Science.

In Honduras and El Salvador, coffee (Coffea arabica) is one of the leading agricultural exports, and the share of specialty coffee is growing each year. However, despite the importance of specialty coffee production and exports, there is a knowledge gap regarding its cost structure and profitability, particularly those associated with labor costs. The specific objectives of the study were to determine the cost structure of specialty coffee in Honduras and El Salvador and to estimate the costs and profitability of producing specialty coffee in these countries. A semi-structured survey instrument was administered to 14 farmers in Honduras and El Salvador selected as a convenience sample to represent different farm sizes, regions, and specialty-conventional and organic production systems. Specialty-conventional refers to high-quality coffee with or without certifications. Then,cost-profitability models were developed using an economic cost approach, which considered cash, noncash cost, and the opportunity costs of inputs. The results showed that although both countries are neighbors and economically and culturally similar, the cost structure of producing specialty coffee differed significantly. Costs were lower and profits were higher in Honduras than in El Salvador, and the specialty-conventional coffee production system was more profitable than the organic production system.

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Coffee Science Foundation Executive Director PETER GIULIANO sat down with DR. MACKENZIE BATALI, lead author of a recent milestone study, “Sensory Analysis of Full Immersion Coffee: Cold Brew Is More Floral, and Less Bitter, Sour, and Rubbery Than Hot Brew,” of the Coffee Science Foundation’s project, “Towards a Deeper Understanding of Cold Brew” to learn more about the process and the results of the study.

Cold-brewed coffee has become a mainstay of the specialty coffee experience over the past decade. Along with the popularity of cold brew, however, has come questions: How does cold-brewed coffee differ from hot-brewed coffee? Are the differences chemical, or sensory, or both? And how can our industry develop guidelines and best practices for excellent cold-brewed coffee?

Read the full article on Nature.com

Because consumers expect their coffee to be hot, but not too hot, operators of coffeehouses, coffee shops, and cafés must make important decisions regarding the serving temperatures for their coffees. Clearly a key consideration is the preferred temperature range expected by consumers, but another important consideration is the risk of scald burns, which can cause tremendous injuries and occasionally result in high-profile litigation. Accordingly, several groups have investigated consumer preferences for coffee versus serving temperature. Borchgrevink et al. examined coffee at seven distinct temperatures evenly spaced between 57.2 and 90.6 °C and collected data on adequacy of serving temperature on a 5-point just-about-right (JAR) scale. They found that of those tested a serving temperature of 68.3 °C yielded an average numerical score closest to JAR. Pipatsattayanuwong et al. examined coffee served at six distinct temperatures over a broader range from 39.2 to 82.1 °C, using pairwise R-index values derived from ranking data, and found that 72.1 °C was the most preferred temperature of those tested. Lee and O’Mahony used a different approach by letting consumers freely mix hot and cold coffee until they obtained a preferred temperature. With this method, they found a much lower preferred temperature of 59.8 ± 8.1 °C, which they hypothesized was due to consumers adjusting the temperature to be suitable for drinking whole mouthfuls of coffee rather than smaller sips. Similar results were obtained more recently by Dirler et al., who also used a free-mixing method and found an average preferred temperature of 63 °C.

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Assistant Professor CHRISTOPHER H. HENDON shares the theory underpinning an ongoing Coffee Science Foundation research project, supported by Simonelli Group, toward deepening our understanding of espresso extraction.

Watch the full session from Re:co 2022 on SCA News

As home coffee consumption continues to increase even as pandemic restrictions ease, so too has our interest in understanding packaging (an element of the coffee experience making its way consistently into the home) through a multimodal lens. Dr. Fabiana Carvalho introduces an ongoing study, conducted in collaboration with the Coffee Science Foundation, exploring the effect of packaging on the perception of specialty coffee and explains why we need to expand our concept of "functional" packaging beyond simply keeping coffee fresh.

Read the full academic paper in Foods, an international, scientific, peer-reviewed, open access journal of food science.

Cold brew coffee is often described as sweeter or less acidic than hot brew coffee. Such comparisons, however, are potentially confounded by two key effects: different brew temperatures necessarily change the extraction dynamics and potentially alter the resulting brew strength, and different consumption temperatures are well known to affect perceived flavor and taste. Here, we performed a systematic study of how extraction temperature affects the sensory qualities of full immersion coffee. The investigation used a 3 × 3 × 3 factorial design, with coffee from three different origins representing different post-harvest methods (washed, honey-processed, and wet-hulled), each roasted to three different levels (light, medium, and dark), and each brewed at three different temperatures (4 °C, 22 °C, and 92 °C). All coffees were brewed to equilibrium, then diluted to precisely 2% total dissolved solids (TDS) and served at the same cold temperature (4 °C). We find that four attributes exhibited statistically significant variations with brew temperature for all origins and roast levels tested, with bitter taste, sour taste, and rubber flavor all higher in hot brewed coffees, and floral flavor higher in cold brewed coffee. However, there were strong interactions with origin and roast, with several additional attributes significantly impacted by temperature for specific origins and roast levels. These results provide insight on how brew temperature can be used to modulate the flavor profile of full immersion coffee.

Read the full article on SCA News.

Lead Author JIEXIN LIANG shares findings of a recent paper, “An Equilibrium Desorption Model for Strength and Extraction Yield of Full Immersion Brewed Coffee,” published in Scientific Reports, that outlines a predictive model for the equilibrium strength and extraction of “full immersion brewed coffee” (cupping) between 80°C and 99°C (176°F and 210°F) and suggests we’re more easily able to control our total dissolved solids (TDS) via brew ratio instead of our extraction yield (E).

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.

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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.

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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 SCA News and 25.

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

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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?