The Chemistry of Gelato

The Chemistry
of Gelato
The structure of gelato:
Ice crystals
Gelato is considered a colloid
or suspension of air and ice crystals
in a sugar solution.
Gelato contains all three states of
matter simultaneously
The process of making gelato:
1. Mixing the ingredients (milk, sugar, flavor and
Ice cream uses heavy cream (12-18% butter fat) but
gelato uses whole milk (4-5% butter fat).
2. Pasteurization – heating to kill bacteria in dairy
3. Homogenization –
breaking the fat globules into
smaller fat droplets. Can be
done in a factory by forcing
the liquid through a small hole
or by hand mixing.
4. Ageing – the stabilizers bind to the surface of the fat
droplets and the fat droplets begin to harden (crystalize).
The stabilizer helps to keep the fat droplets small after
they’ve been broken up, by binding to the surface of the
5. Churning and freezing – air is added to the mixture
while the temperature is lowered. Gelato contains much
less air (30-40%) than ice cream (50%) which
contributes to its creamier texture. It is also served at a
higher temperature.
The fat droplets partially crystalize and help to stabilize
the air bubbles.
Sugar lowers the freezing temperature of the water.
As more water is removed from the solution (frozen) the concentration
of sugar increases and lowers the freezing point even more.
Ice cream scientists use the freezing point curve when formulating
ice cream recipes. Suppose, for example, they want to make 1 kg of
ice cream that contains 50 per cent ice by weight at a normal freezer
temperature of -18°C. How much sucrose should they use? From the
curve, the sucrose mole fraction in equilibrium with ice at -18°C is
0.083 or 63 per cent w/w, ie:
Msucrose /(Msucrose + Mwater) = 0.63
The total mass is 1 kg, and 50 per cent of this will be ice, so the
remainder, must be sucrose and unfrozen water.
Msucrose+ Mwater = 500 g
Solving these two equations gives Msucrose = 320 g.
Freezing must be done quickly so that the ice crystals formed
are as small as possible.
Ice crystals at -10°C
Ice crystals warmed to -7°C
Ice crystals re-cooled to -10°C

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