Effect of milk processing and steam frothing conditions on microfoam formation

This study focuses on the evaluation of microfoam produced from processed dairy milk using the steaming function of the espresso machine as a function of temperature (30 – 80°C), milk type (pasteurised or UHT), and whey protein contents. Foam characteristics, i.e., foam stability, viscosity, bubble size distribution noticeably varied depending on milk processing type and steam heating temperature. Foams made from pasteurised whole milk tend to be more stable. Bubbles in pasteurised milk foam were better distributed, especially at the temperature of 60°C. It was observed that the optimal final temperature of steam frothing was in the range of 50°C to 60°C. The results of sensory tests show that consumers differentiated between the aroma and flavour of pasteurised and UHT milk, describing the degree of this difference from moderate to strong. The technique of freeze-distilling (FD) milk was first used at the World Barista Championship 2017. This method is mainly used to intensify the flavour of milk by reducing the amount of water in the milk. The analysis of freeze-distilled milk samples demonstrated the increase in protein and lactose concentration in both pasteurized and UHT milk samples. Particle size distribution was not significantly affected by freezing of milk samples within 24 h with the subsequent thawing. Freeze-distillation also showed no significant effect on milk foaming properties in terms of microfoam expansion, stability, and overrun. The results of the triangle test showed that panellists could distinguish between cappuccino samples made with regular and freeze-distilled milk for both pasteurized and UHT milk types. Assessors described freeze-distilled samples as sweeter, more intense, and rich.