Here's The Science - Making Sorbet Using Dry Ice
When the ice cream mixture is chilled water ice crystals start to form and this continues through the chilling process. When an ice crystal is formed it attracts surrounding moisture to it and therefore grows in size. The objective is to create lots of small ice crystals so that the resultant ice cream feels smooth and creamy in your mouth, rather than fewer larger water ice crystals that will feel gritty and sharp in the mouth. For this reason it is necessary to chill down the contents as quickly and evenly as possible. We do not want to risk anyone putting dry ice in their mouths so it is important to wait at least one hour before consuming. The sorbet must therefore be stored in a freezer, however if you do this it will turn rock hard and be horrible. This is where gelatin comes in. The collagen in the gelatin softens the mixture allowing the sorbet to be spoon cut from the freezer.
Food grade dry ice for chilling down is a good choice as it is very cold and can be mixed into the bulk of the mixture. Dry ice works best with fruit flavoured ices and sorbets, this is because any residual CO2 absorbed into the smoothie from the dry ice causes a slight tartness on the tongue due to formation of carbonic acid with water which complements fruity flavours.
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