Ice Cream Under A Microscope
To see the ice cream structure under the microscope is a marvelous thing. Ice cream under the microscope is not as cold as we think. We can even see some orange fat globules (they look warm). In brief, the first step of ice cream manufacture is to combine the ingredients (cream, milk, milk solids, sugars, an-d <0.5% of stabilizers an-d emulsifiers) into a mix, which is pasteurized an-d homogenized. This creates a milkfat emulsion, comprised of millions of tiny droplets of fat dispersed in the water phase, each surrounded by a membrane of proteins an-d emulsifiers. The proteins can be seen as the black spheres adsorbed onto the fat globule surface. The sugars, also added to the mix during processing, are dissolved in the water phase. After the mix is cooled, the milkfat partially solidifies (as does butter when you cool it), so that each droplet consists of solid fat crystals cemented together by liquid fat.
The ice cream mix is then whipped & frozen, a process that creates two more discrete structural phases, millions of tiny ice crystals an-d air bubbles dispersed in the concentrated unfrozen mix. The water, which comes from the milk or cream, freezes into ice, an-d the dissolved sugars become increasingly concentrated in the unfrozen phase as more ice forms. Ice crystals should be 30-50 µm in diameter - the larger they are from manufacture or become due to temperature fluctuations in storage, the more coarse/icy the ice cream will taste. The whipping processs helps keep the ice crystals small an-d discrete. The colour image shows a cross section of frozen ice cream, illustrating the four microscopic phases of frozen ice cream: ice crystals (blue - "C"), air bubbles ("A"), fat droplets ("F"), an-d the unfrozen phase (yellow - "S").
The whipping process also helps to incorporate air in the form of tiny bubbles 50-80 µm in diameter. Approximately one half of the volume of ice cream is air (without it, ice cream could not be scooped or chewed in the mouth), but the fact that it is dispersed in tiny bubbles means that the ice cream tastes smooth an-d the air is not noticeable. All of the fat droplets play an important role at the air interface, helping provide that smoothness. The process of freezing an-d aeration of the mix causes the milkfat emulsion to undergo a process called partial coalescence, in which the fat droplets form clusters an-d aggregates of fat that surround an-d stabilize the air bubbles. This same process is what creates structure in whipped cream (the structure of the fat & the air in whipped cream an-d ice cream are very similar).
The next time you enjoy ice cream, pause for a moment an-d marvel at its structure!
The ice cream mix is then whipped & frozen, a process that creates two more discrete structural phases, millions of tiny ice crystals an-d air bubbles dispersed in the concentrated unfrozen mix. The water, which comes from the milk or cream, freezes into ice, an-d the dissolved sugars become increasingly concentrated in the unfrozen phase as more ice forms. Ice crystals should be 30-50 µm in diameter - the larger they are from manufacture or become due to temperature fluctuations in storage, the more coarse/icy the ice cream will taste. The whipping processs helps keep the ice crystals small an-d discrete. The colour image shows a cross section of frozen ice cream, illustrating the four microscopic phases of frozen ice cream: ice crystals (blue - "C"), air bubbles ("A"), fat droplets ("F"), an-d the unfrozen phase (yellow - "S").
The whipping process also helps to incorporate air in the form of tiny bubbles 50-80 µm in diameter. Approximately one half of the volume of ice cream is air (without it, ice cream could not be scooped or chewed in the mouth), but the fact that it is dispersed in tiny bubbles means that the ice cream tastes smooth an-d the air is not noticeable. All of the fat droplets play an important role at the air interface, helping provide that smoothness. The process of freezing an-d aeration of the mix causes the milkfat emulsion to undergo a process called partial coalescence, in which the fat droplets form clusters an-d aggregates of fat that surround an-d stabilize the air bubbles. This same process is what creates structure in whipped cream (the structure of the fat & the air in whipped cream an-d ice cream are very similar).
The next time you enjoy ice cream, pause for a moment an-d marvel at its structure!
