What makes ice-cream get icicles?
Author: Lisa Featherby
"I made the raspberry
ripple and white chocolate ice-cream cake for Christmas Day.
Whilst the flavour was lovely, why did it have icicles throughout
it? Was it the milk in the recipe and the fact that you were asked
to place cling film over the top that was the cause? It looked
wonderful, but after the effort I was sorely disappointed."
Fiona, Tweed Heads, NSW
Lisa Featherby, Gourmet Traveller senior food editor, writes:
Ice-creams can turn icy for a number of reasons. An ice-cream base is usually made up of milk, egg yolks, sugar and cream. Milk fats in the cream and milk become solid globules when frozen and provide the ice cream with a depth of richness and creaminess, whereas the water component in milk can become icy if the following has not taken place.
First, it's important to cook out your anglaise (custard)
properly. The cooking out process aids in the following, it ensures
that the sugar is dissolved (sugar lowers the freezing point of the
ice-cream mix making it softer, if the sugar has not been dissolved
properly into the mix, this can cause an uneven result in the
texture), it binds the egg yolk and liquid and in turn thickens the
custard (the egg yolk acts as a stabiliser by thickening the
custard and binding during cooking, creating a smoother texture to
the final result), and it causes excess water to evaporate during
cooking (water turns to ice when frozen).
The way to combat the faults caused through this first step is to cook out your anglaise thoroughly, a longer cooking time over a lower heat is the best method. You can also cook out your anglaise over a higher heat and for less time, but you will need to be careful not to split your mixture: continuous stirring is very important here and having a chilled bowl ready to stop the cooking process immediately when your mixture is ready is advisable. The mixture, when ready, should be thick enough to coat the back of a wooden spoon to the point that, when you run your finger through the coating, you should leave a definite line. Also, if you overcook your anglaise, it will curdle or split, causing the water to separate from the protein. Undercooking also creates an icy texture as the above mentioned has not taken place.
Secondly, the mixture needs to be chilled and churned properly. Using an ice-cream churn is the best method, as the churning process freezes the mixture while aerating the mix. Aerating the mix traps the solid and liquid particles between air cells and in turn softens and lightens the mix. Overchurned ice-cream can overdevelop the fat molecules also which basically turns cream to butter, this won't affect the iciness, but will affect the texture of the ice-cream.
Lastly, the temperature your ice-cream is stored and for what length of time can affect ice particles developing. Ideally ice-cream should be stored at -18C to -23C for best results. With sugar present in the mixture the ice-cream will not freeze 100%, therefore if the temperature fluctuates or falls below the desired temperature it can cause the ice-cream to melt and in turn create ice particles. If home made ice-cream is kept for a long period of time, this can be caused through freezers being opened and closed, as there is no artificial stabiliser present in home made ice-cream. Covering the ice-cream directly with plastic wrap will also help to prevent ice particles forming on top.