Erythritol is a type of sugar alcohol that is keto-friendly. However, erythritol also has a low freezing point, which means that it can make ice cream harder to scoop. When erythritol is combined with other ingredients like milk and cream, it forms microscopic crystals that are difficult to scoop.  If you want to use erythritol or a blend that contains it (such as Swerve), plan on taking your ice cream out of the freezer about 15 minutes before serving.