Investigation of the factors affecting foamability and foam stability of cold brew coffee

In this study, the foamability and foam stability of nitrogen-infused cold brew coffee, as affected by coffee variety (Arabica and Robusta), degree of roast (light, medium, dark), brewing temperature (4, 20, 35 °C), brew ratio (1:5-1:15 w/w; coffee/water), ground particle size (712, 647 and 437 μm volume mean diameter) and beverage temperature (4, 20 and 35 °C), were investigated.

Dynamic surface tension of cold brew, as determined from bubble tensiometry, decreased from 65-70 mN m^-1 to about 60 mN m^-1 as the bubble lifetime increased from 0.1 s to 1 s. Infusing the cold brew coffee (70 mL) with nitrogen gas for 30 s at 50 mL min^-1 generated 30-40 mL of foam head. At the same degree of roast, brews prepared from Arabica beans had more stable foam than those from Robusta. Foam stability increased with increasing degree of roast, increasing brewing temperature, decreasing particle size, and decreasing the beverage temperature. By contrast, brew ratio had relatively less effect on foaming properties. Nitrogen-containing constituents present in the 80% (v/v) ethanol-soluble fraction (55.9% of total dissolved solids) of the brew samples were important contributors to foaming, while the 80% (v/v) ethanol-insoluble fraction (42.3% of total dissolved solids) that contained polysaccharides was important in stabilizing the foam.

The foamability and foam stability of cold brew coffee are significantly affected by coffee variety, degree of roast, brewing temperature, ground particle size, and beverage temperatures. The foam properties are dictated by the low-molecular-weight nitrogen-containing compounds and high-molecular-weight polysaccharides present in the cold brew coffee. © 2022 Society of Chemical Industry.