What is an ice cream?
Ice cream is a complex system of foam, containing a gas (air) dispersed as small cells in a partially frozen continuous phase. In the continuous phase fat is dispersed as an inner phase in an emulsion, where the milk solids and stabilisers are in a colloidal solution and sugar and salts form a true solution.
The importance of air in ice cream
Air is an important component in ice cream affecting the physical and sensory properties as well as the storage stability. Ice cream normally has around 100 % overrun meaning that the air makes up 50 % of the ice cream volume. The amount of air incorporated into the mix influences the sensory attributes of the ice cream. If a lower amount of air is applied, the resulting ice cream is dense, heavy and more cold eating.
If a higher amount is used, the texture is lighter, creamier and more warm eating.
Producing ice cream with a high overrun
Production of ice cream with high overrun is an interesting tool for cost saving. However, the perceived quality by the consumer has to be kept in mind. The sensory attributes such as creaminess and smoothness as well as resistance to shrinkage and melting cannot be compromised as these properties are very closely linked to consumer preferences.
Creaminess as well as melting resistance is related to the distribution of air cells in the product. A more uniform air cell distribution in the ice cream results in a creamier and slower melting ice cream. Emulsifiers like mono- and diglycerides are well known for their positive influence in this respect.
The effects of emulsifiers
Production of ice cream with high overrun means, other things being equal, that the cell walls around the air cells are thinner and weaker. It is therefore at high risk production of very high overrun ice cream takes place. However, by choosing the right emulsifiers and stabilisers it is possible to manufacture an ice cream with high overrun which will still be perceived as a high quality ice cream.
Especially the emulsifier plays an important role: Emulsifiers are surface active ingredients due to their hydrophilic-lipophilic properties. Consequently, they place themselves in the interfacial layer between the fat/protein and water. The main functionality of emulsifiers in ice is to destabilize the fat globule membrane covering the fat globules formed during homo-genization of the ice cream mix. During ageing the proteins covering the fat globule are replaced by emulsifiers. Hereby agglomeration and partially coalescence of the fat globules is facilitated. This is important for the structure formation and air cell distribution formed during whipping and freezing. Further emulsifiers are important for the stability of the formed air cells i.e. the strength of the air cell walls.
In short terms the functionality of the emulsifier in ice cream is seen as:
- Improved fat emulsification in the mix
- Controlled fat agglomeration and coalescence
- Facilitated air incorporation
- Improved dryness on extrusion
- Improved melting resistance
- Improved heat-shock stability
- Improved smoothness and creaminess