Step 1: Cook the Grapes

1. In a large saucepan, combine Concord grapes and water. Heat over low flame until the grapes release their juices and start bubbling.
2. Gently mash the grapes with a wooden spoon to break them down further. Let the mixture cool slightly.
3. Blend the cooled mixture briefly, then strain it through a fine-mesh sieve to remove seeds and skins, leaving a smooth grape juice.

Step 2: Prepare the Custard Base

1. In another saucepan, combine heavy cream, milk, half the sugar, and a pinch of sea salt. Heat over medium flame until steaming but not boiling.
2. In a separate bowl, whisk egg yolks with the remaining sugar until pale and creamy. Gradually add a small amount of the hot cream mixture to temper the yolks while whisking continuously.
3. Pour the tempered yolks back into the saucepan with the remaining cream mixture. Cook over low heat, stirring constantly, until it thickens enough to coat the back of a spoon (about 5–7 minutes). Avoid boiling.
4. Stir in the cooled grape juice until fully combined.

Step 3: Chill and Churn

1. Transfer the custard to a large mixing bowl and let it cool completely at room temperature before refrigerating for at least 4 hours or overnight.
2. Once chilled, churn in an ice cream maker according to manufacturer instructions until it reaches soft-serve consistency.
3. Transfer to an airtight container, cover with plastic wrap touching the surface to prevent ice crystals, seal tightly, and freeze for at least 4 hours or overnight.