Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee

Abstract

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.

Consumer preferences for black coffee are spread over a wide range of brew strengths and extraction yields

“…The three factors were BT, TDS and PE, each with a “low”, “medium,” and “high” level, which was defined in terms of a physical parameter (Table 1). These specific values were chosen to be consistent with the complementary sensory descriptive analysis study (Batali et al., 2020).…”

“…Details on the roast conditions are available in Batali et al. (2020). All coffee was stored in vacuum sealed plastic bags in a −20 o C chest freezer to minimize aroma loss and staling (Cotter & Hopfer, 2018), and removed from the freezer the night before and allowed to thaw at room temperature for no less than 12 h prior to brewing.…”

“…Consumers were then provided with a check‐all‐that‐apply (CATA) list of 17 attributes ( Sweet, Sour, Bitter, Astringent, Thick/Viscous Tea/Floral, Fruit, Citrus, Green/Vegetative, Paper/Woody, Burnt, Cereal, Nutty, Dark Chocolate, Caramel, Roasted, Rubber ) and were asked to describe the flavor of the coffee by selecting the relevant terms from that list. Those 17 attributes were selected from our descriptive analysis of the same coffees (Batali et al., 2020), and to stay within the typical number of attributes (13 to 20) for a CATA descriptive task with consumers. Finally, consumers indicated purchase intent ($3 for a 360 mL cup) using a 5‐point bipolar scale.…”

“…External preference maps were created to investigate which attributes positively or negatively drove liking for each of the consumer clusters. For each cluster, average overall liking scores were calculated for all products, and then regressed onto the principal components of a PCA of descriptive analysis ratings of the coffees (Batali et al., 2020). For comparison purposes, an external preference map was also constructed based on the product space created by correspondence analysis (CA) of the CATA attributes selected by the consumers that varied significantly among the coffees (determined by Cochran's Q Test).…”

“…Furthermore, despite roast level being the largest driver of flavor differences, some attributes displayed similar trends across brewing profiles regardless of roast. In a similar experiment (Batali, Ristenpart, & Guinard, 2020), we used a single roast and instead varied the brewing temperature while adjusting other brew parameters (grind size and flow rate) to achieve the same TDS and PE. We concluded that TDS was the largest driver of differences in coffee flavor out of the three variables.…”