Final Examination for the Degree of MSc - DONGNING YU

Examining Committee

Dr. Douglas Goff, Chair
Dr. Loong-Tak Lim, Advisor
Dr. Fernanda Peyronel, Co-Advisor
Dr. Maria Corradini, Department Member

TITLE: FOAMING PROPERTIES OF COLD BREW COFFEE

ABSTRACT: The foaming properties of cold brew coffee have been investigated in this study. The variables investigated were coffee variety, roast degree, brewing temperature, brewing ratio, coffee particles of grinder setting, brew temperature, and brewing methods. The initial foam volume generated, by sparging cold brew coffees with nitrogen gas at ambient pressure, range from 37.0±1.0 to 47.0±0.5 mL for beans roasted from light to dark roast degree, respectively. The higher foam volume in dark roast was correlated with higher nitrogen content (0.260±0.002%) and lower surface tension (51.5±0.1 mN/m) of the brews than the nitrogen content (0.160±0.002%) and surface tension (54.5±0.2 mN/m) of light roast brew. Moreover, brews from darker roast beans had more stable foam than those brewed from lighter roast beans, which can be attributed to the higher viscosity (1.150±0.001 mPa.s) and higher total sugar content (6.78±0.11 mg/mL) in dark roast brew compared with the viscosity (1.110±0.001 mPa.s) and total sugar content (6.29±0.20 mg/mL) of light roast coffee brew. Foams from Arabica coffee brews were more stable than those of Robusta coffee. To further investigate the effects of chemical compositions on the foaming properties, the cold brew samples were further precipitated with ethanol. The reconstituted supernatant fractions from the ethanol precipitation treatment contributed to the foaming of the brews, but not the reconstituted precipitate fractions. The reconstituted supernatant fractions gave a higher nitrogen content (0.150±0.002%) and lower surface tension (69.55±0.32 mN/m) than the nitrogen content (0.030±0.001%) and surface tension (50.82±0.18 mN/m) of the reconstituted precipitate. By contrast, the reconstituted precipitate fraction exhibited properties important in stabilizing the foam, which can be attributed to the higher total sugar content (2.98±0.11 mg/mL) than that of the reconstituted supernatant (2.30±0.10 mg/mL). This study will investigate the factors that affect the foam properties of cold brew coffee, and discuss the physicochemical what behind cold brew coffee foam.