Dairy Science Information

Ice cream: structure of ice cream

The smoothness, body and "scoopability" of ice cream all come down to its microstructure. Ice cream is not a simple frozen liquid – it is a complex, partly-frozen foam made up of four elements held together in a delicate balance:

• Ice crystals – frozen water; their size is the single biggest factor in perceived smoothness.
• Air cells – whipped in during freezing (the overrun); they give ice cream its light body.
• Fat globule network – partially coalesced fat that stabilises the air cells and gives a creamy mouthfeel.
• Unfrozen serum phase – a concentrated solution of sugars, proteins and stabilisers that never fully freezes.

Ice cream crystallisation

Fast freezing rates promote the formation of many small ice crystals, which the tongue cannot detect individually – this is what makes ice cream taste smooth. Slow freezing results in larger crystal formation, which is sometimes desirable in granita-type products but is a defect in standard ice cream.

The crystals continue to evolve after the ice cream leaves the freezer. Temperature fluctuations during storage and distribution – known as heat shock – cause small crystals to melt and re-freeze onto larger ones (recrystallisation). Over time this coarsens the texture and produces the icy, grainy mouthfeel of poorly stored ice cream. Stable, low storage temperatures and effective stabilisers are the main defences against it.

What controls crystal size and texture

• Freezing rate – faster freezing means smaller crystals and a smoother product.
• Storage temperature stability – fluctuations drive recrystallisation and grain.
• Overrun – the amount of air whipped in affects body and meltdown.
• Fat and emulsifiers – control the fat network and air-cell stability.
• Stabilisers – manage the unfrozen water and slow heat-shock damage.

Ice cream structure: frequently asked questions

What makes ice cream smooth or icy?

Crystal size. Many tiny ice crystals feel smooth; large crystals feel icy. Fast freezing creates small crystals, while slow freezing or temperature fluctuations in storage make them grow.

What is heat shock in ice cream?

Heat shock is the damage caused by temperature fluctuations during storage and transport. Small ice crystals melt and re-freeze onto larger ones, coarsening the texture over time.

Why is granita coarse on purpose?

Granita is frozen slowly and deliberately to grow large ice crystals, giving it its characteristic crunchy, granular texture – the opposite of what is wanted in smooth ice cream.

For more information or to discuss your requirements please contact us.