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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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).

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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 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.

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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.