Aeration experiments were conducted for a gelatin solution and a food emulsion. The change in the overrun (the amount of air incorporated into the continuous medium) was monitored, and the bubble size distribution was measured using the advanced image analysis technique for various stages of the aeration process. The aeration process consists of two regimes: the incorporation of large bubbles into the continuous medium and the breakage of the incorporated bubbles. The bubble dynamics during the aeration process were modeled using the population balance equation. The breakage frequency and coalescence rate (which is required to solve the population balance equation) are obtained from the modification of the formula derived by Vennerkar et al. (AlChE J. 2002, 48, 673). The sizes of the broken bubbles (daughter bubbles) are calculated with consideration of the breakage of the bubbles inside the aerating vessel as a result of the Rayleigh-Taylor instability phenomenon. The energy consumption rate, which is the parameter connecting the breakage frequency and the coalescence rate with the properties of the continuous medium and the aeration conditions, is derived from the power relation inside the aerating vessel. The prediction of the change of the bubble size from the model is in good agreement with the experimental observation during the aeration process.