This is such an easy, quick and most importantly – mess free method to make ice cream with kids. And it is so very, very fast. The scientific bit is that you need to make sure that you add salt to the ice – this is often ignored and forgotten but it is essential.
The ice will allow the water to still be liquid at temperatures below zero and so the water becomes the engine that drives the freezing. Try is without salt and you will see what I mean.
The gently agitation as the you let it freeze has a similar effect to that of cream chargers in that it helps cream molecules to coalesce and thicken – you can literally feel it happen in your hands – which is part of the reason why ice cream in a bag is such a great idea for kids there is no secret, hidden process – everything is right in front of you eyes.