“For drinkers to enjoy the foam, it needs to stick around. Although the foam lasted the longest for the highest temperature and pressure studied, the relationship wasn’t as straightforward as it was for foam formation. For pump pressures of 1 bar and 0.5 bar, the foam stability was higher at the intermediate temperature of 10 °C than at 15 °C.
“The reason is the distribution of bubble sizes. At lower temperatures, the bubbles have a fairly uniform size, but at higher temperatures, the sizes vary. The pressure difference between neighboring large and small bubbles causes the large bubbles to siphon off the small bubbles’ gas until the small bubbles wither away. And thus the foam dissipates faster.”