Instant coffee foam: An investigation on factors controlling foamability, foam drainage, coalescence, and disproportionation

摘要

Foamability and foam stability mechanisms of instant coffee foam were elucidated by varying the total solid content (10-40% w/w), gas flow rate (0.2-0.5 L/min) and gas sparging time (30-45 s). Maximum foam volume obtained after gas sparging was used as the measure of foamability. Foam stability was estimated from the rates of foam drainage, bubble coalescence, and disproportionation. Foamability was majorly influenced by the gas flow rate. Coffee foam exhibited three patterns of destabilization: (a) coalescence; (b) coalescence followed by disproportionation; and (c) partial coalescence. Differences in the mode of coffee foam destabilization can be attributed to the variations in initial bubble size and the manner in which the bubble size distribution evolves with time. The optimum conditions to obtain maximum foam volume and stability were 10% solid content of coffee solution, 0.4 L/min of gas flow rate, and 33 s of gas sparging time.