Effects of brew strength, brew yield, and roast on the sensory quality of drip brewed coffee

Abstract

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. Practical Application This research provides guidance on how best to achieve specific flavor profiles in drip brewed coffee.

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

“…The amount of water used to brew was kept consistent at 3075 g of water, while brew ratio was varied by changing the mass of ground coffee. Brew ratios, grind, and duty cycles were chosen through preliminary trials on the study coffee reach the exact target TDS and PE, guided by brew recipes published by Frost et al on the same brewers 15 . All of the specific brew settings for each of the 27 samples, including brew ratio, grind size, duty cycle, and brew temperature, are listed in Supplementary Table 1.…”

“…Grind sizes corresponding to the settings 3 (fine), 4 (medium), and 5 (coarse) on a Mahlkönig Guatemala Lab Grinder (Mahlkönig USA, Durham, NC, USA) yielded average particle grind sizes of 770 ± 10 µm, 928 ± 3 µm, and 1115 ± 74 µm; see Frost et al . 15 for detailed grind size distributions. Extraction was controlled between temperatures, so grind, brew ratio of water to coffee, and water pulsing duty cycle were adjusted at different brewing temperatures.…”

“…Calibration experiments with oven-drying of brewed coffee samples confirmed that the digital refractometer yielded accurate measures of the TDS (see Frost et al . 15 for details). The total delivered mass of the brewed coffee was measured after each brew, and the percent extraction was calculated 3 as: …”

“…1) 2 . A more recent study suggests that Bitter taste and Viscous mouthfeel increase with both TDS and PE when generalized across multiple different roast levels, though the dependence changed with individual roasts 15 .…”

“…Batali et al examined the role of TDS via temporal fractionation of a drip brew, and found that attributes like bitter, sour, and smoky were positively correlated with TDS, while attributes like sweet, fruity, and floral were negatively correlated with TDS 14 . Most recently, Frost et al characterized the impact of TDS and PE on sensory quality of drip brew for three different roast levels, and found similar trends-generally more bitter and sour at higher TDS, and sweeter at lower TDS, regardless of roast level 15 .…”