Ice cream - The four microstructure elements - Ostwald ripening and accretion
9 important questions on Ice cream - The four microstructure elements - Ostwald ripening and accretion
Which 2 instability effects occur in ice cream?
- Air bubbles growth
- Coalescence
- Disproportionation
- Ice crystal growth
- Recrystallisation (when T changes)
- Accretion (coalescence)
- Ostwald ripening (disproportionation)
Why is ice cream or sorbets white?
How is the stability of air bubbles related to the colour of ice cream?
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What are the 2 effects of unstable air bubbles in ice cream?
- Whiteness will decrease, as larger air bubbles scatter less light.
- Softness of the ice cream will change.
Which 2 instability mechanisms lead to a change in air bubble size?
- Coalescence --> when air bubbles are not stabilised and interface is not strong enough --> lower incorporation of air and collapse of ice cream
- Disproportionation --> imbalance of pressure between air bubbles. LaPlace pressure larger in smaller bubbles.
Why does coalescence of air bubbles in ice cream not give spherical shapes?
What happens when ice cream is put in the airplane and taken out again?
When the pressure is restored, the volume will decrease again, which will lead to an additional collapse.
Why does Ostwald ripening occur in ice crystals?
Freezing and melting is in equilibrium.
- some water molecules turn into ice, some molecules turn from a solid form to a liquid form
- Influenced by solubility of ice in water.
- Smaller crystals, solubility is larger.
- Around small crystals the ice melts faster than around large crystals.
- More melting and lower degree of crystallisation around small crystals.
- Less melting and more crystallisation around large crystals.
How can (re)crystallisation be prevented?
- They hinder water molecules from approaching each other. So they keep the ice crystals already smaller.
- They increase the viscosity of the serum phase, which decreases the diffusion of the water molecules (diffusion coefficient). This will decrease the Ostwald ripening rate, so less growth of ice crystals
By ice structuring proteins/anti-free proteins.
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