Ice cream in definition has 7 categories: fat(dairy or nondairy), milk-solid-non-fat(minerals, lactose, protein, vitamins,), sweeteners, stablisers, emulsifiers, flavour, and water. Fat consist of fatty acids,in which 95.8% are tyiglycerides. Glycerides are compounds in which one, two or three fatty acid molecules, named mono-, di- and tri-, glycerides, respectively, are linked by ester bonds with trihydric alchol, glycerol. Nutritionally, fat has a lot of benefits. It supplies energy, essential fatty acids, fat-soluble vitamins, saturated and unsaturated fatty acids, including cholestrol. In ice cream, the role of fat is to mainly build a structured body to discard or slow down the process of ice recystalisation, lubricate the mouth during consumption, thus to improve the texture.
1. Delivering smooth and creamy texture
A high quality ice cream requires numerous tiny ice crystals after dynamic churning in the ice cream machine. If the ice crystal size is big to be perceived as coarse during consumption, it is very likely that the composition is not balanced or there is other technical problems from machines. As fat can lubricate the palate, the small ice crystals is not perceived by our tongue. In my experiments of making reduced-fat ice cream (8-10% fat rate) with a semi-commercial ice cream machine, the perception of ice crystals, under an identical composition with other ingredients unchanged, is much obvious compared to another sample whose fat rate is around 14%. The latter one is just so smooth whilst the former is slightly coarser.
2. Slow down the process of ice recystalisation
Ice cystalisation is a process that undergoes during the dynamic agitation inside the ice cream machine where the powderful srapper blade and the rotating dash keep pumping air in the mix, and it is this time the tiny ice crytals form and spread to the product. Recystalisation is the process that only happens during static storage, i.e in the blast freezer where some ice cystals formed in dynamic agitation melt and fuse together with the larger ones, becoming an even larger ice crystal until the time when the tongue can perceive its existence during consumption, it is very likely that the product has spoiled.
3. Stablise the air bubbles in ice cream
Air is one of the key elements in ice cream, even though it cannot be seen, smelled or touched. Ice cream without air is a pasteurised viscous liquid mix that cannot deliever that fluffy, sort of chewy texture. As in the mix there is protein that emusifies and crystalises the fat during the process of aging*, these fat globules starts destablised when churning process is begun that the air is then trapped and surrounded by them - ideally in a massive amount but small size. The whipping properties from fat will be weakened without sufficient fat, the frame thus will also be collapsed, the air bubbles are then not stablised to deliver the firm texture.
*Aging: Mix after pasteurisation set in the fridge at below 5°C for at least 8 hours so that the fat globules can be fully emulsified and cystalised.
4. Prolong the melting time
When the frame is supported by fat and air, with other ingredients in a balanced composition, the melting time is much longer than an unbalanced composition and the end product is likely to be slurry-like instead of a dry, clean and bright surface.
Summary
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