Freshly made ice cream owes its smoothness to a large number of small ice crystals. In storage, the small crystals shrink and the large ones grow, a process called recrystallisation. Once the crystals are big enough to detect on the tongue, the ice cream tastes icy or coarse, even though nothing has been added or taken away.

What happens in the freezer

A study in the Journal of Food Engineering followed two commercial ice creams for 154 days at four storage temperatures and three sizes of temperature swing. Recrystallisation was faster at warmer storage temperatures and with larger temperature fluctuations. Mean crystal size grew steadily with time, following the pattern expected for crystals coarsening in storage.

That puts the cold chain first. Every door opening, defrost cycle, loading bay and transfer to a retail cabinet is a small temperature swing, and the swings add up.

What stabilisers do

Stabilisers slow recrystallisation, but not simply by thickening or gelling the mix. Research on model systems points to several effects at once.

  • Gelling is not the explanation. In sugar solutions without milk solids, alginate and xanthan slowed recrystallisation significantly. With milk proteins present, every stabiliser tested was effective except gelatin, and a non-gelling stabiliser, xanthan, outperformed a gelling one, gelatin. The authors concluded that interactions between the polysaccharides and milk proteins appear to be key.
  • Milk proteins change the picture. In dynamically frozen model systems, xanthan and locust bean gum were most effective without milk proteins, but with them only xanthan had an effect. Separation between the biopolymers concentrated milk proteins at the ice crystal surface, which appeared to strengthen the stabiliser's effect.
  • More stops helping. In model solutions, increasing the stabiliser concentration slowed recrystallisation until a point where adding more had no further effect. Both gelling and non-gelling stabilisers worked, which the authors took as evidence that stabilisers act at the ice crystal surface.
  • Some stabilisers build structure in the cold. Locust bean gum formed weak gel structures when solutions were cycled between freezer temperatures, especially with milk solids present, while guar did not. Fat droplets interfered with that network.

In the long storage study, the ice cream stabilised mainly with carrageenan seemed more effective at slowing crystal growth than the one stabilised mainly with locust bean gum. The researchers behind the cryo-gelation work add a caution that applies to all of this: model solutions behave differently from real ice cream, so results have to be confirmed in the actual mix.

Beyond classic stabilisers

A 2016 review of frozen dairy desserts lists newer tools used to control ice recrystallisation and texture, including dietary fibres, other polysaccharides, prebiotics, alternative sweeteners and ice structuring proteins, alongside emerging processes such as high pressure and low temperature extrusion.

Testing a fix

  • Make the control and the test on the same day, on the same freezer.
  • Store both through the same temperature cycling, set to resemble your real distribution chain.
  • Judge iciness at fixed ages, by crystal size where you can measure it and by a trained panel where you cannot.
  • Change one thing at a time: the stabiliser, the level or the storage, never all three.