Sorbet is prepared by freezing a mixture of water and fruit, sometimes with a generous dash of alcohol. Asti Spumante is ideal for this, as it is a sweet, sparkling dessert wine. It is Italian in origin, and a popular variety is sold under the Martini brand. The quality of the wine has been said to decline in recent years due to EU regulations, but it would certainly have been at its best at the time our story is set.
Here is a recipe for muscat grape sorbet.