Make refining sugar from the mineral water and sugar (bring to the boil, dissolve the sugar and let it cool). Thaw the forest berries covered with a little sugar, puree and add to the sugar syrup. Beat the egg white with a pinch of salt, not too firm, and stir in as well.
If the ice cream machine is working, pour it into the same and when the mass begins to crystallize, gradually add the grappa. Note: Depending on the quality and alcohol content, the freezing time can be considerably longer.
Without an ice cream maker, it is best to put everything in a metal bowl in the freezer and stir every quarter of an hour with the whisk. Only when the mass starts to freeze, gradually add the grappa.