Ice Cream

Ice cream is a popular dessert, which owes its sensorial properties (mouth feel) to its complex microstructure. The microstructure is a result of the combination of the ingredients and the production process. Ice cream is produced by simultaneous freezing and shearing of the ice cream mix, which results in the formation of ice crystals, air bubbles and a viscous serum phase. The amount and the size of the ice crystals and air bubbles have significant contributions to the mouth feel, the melting behavior, ease of spooning, etc. It also affects the shelf-life of the products. Therefore, control of the particle size and volume fraction is crucial. The ice crystals have a large influence on the hardness of the ice cream. The particle size, which is normally in the range of 30–50 µm, determines the degree of coldness, which can be controlled by the temperature of the production process. A wide particle distribution will have a negative influence on the shelf-life, as Ostwald ripening and recrystallization will occur more often. Once the recrystallization processes lead to the growth of larger ice crystals above 100 µm, the ice cream will feel icy and gritty. Therefore, to increase mouth feel and shelf-life, a narrow size distribution of small ice crystals is preferred. The air bubbles, in the size range of 20–50 µm, provide the softness and decrease the coldness of the ice cream, and are usually present in high volume fractions. Due to a high volume fraction, the air bubbles are in close proximity, thereby enhancing coalescence. Once coalescence has led to the increase in air bubble size and the formation of channels, the air can escape and the ice cream collapses. Ostwald ripening, due to a wide particle size distribution, will enhance this effect. Once the air has escaped, the ice cream will become harder. As the air is non-conductive, the presence of air slows down the heat transfer, leading to a warmer mouth feel for ice cream with a high volume fraction of air. The collapse of the ice cream will therefore also change the mouth feel from a slightly warmer to a colder ice cream. To increase the shelf-life and mouth feel, the air bubbles should be stabilized. This can be accomplished by coating the air bubbles with fat globules. During the production process, the fat globules will partially coalesce, thereby forming a fat layer around the air bubbles. The process is enhanced by a decrease in fat globule size (to sizes below a micrometer), which is controlled by homogenization of the ice cream mix. To enhance shelf-life and control mouth feel, the particle size and its distribution is important for all elements in the ice cream