Nonalcoholic Substitute for Marsala Wine
I have cooked quite a few times for Islamic guests and finding non alcoholic substitutes for wine is never easy. In general you find a lot of solutions floating around on the Internet based on grape juices, but I have never been quite satisfied with the results that brings me.

My best results have been achieved through using non alcoholic wine instead of grape juice. Especially the brands of non alcoholic wine that are produced by chemically extracting the alcohol from the finished product come quite close to behaving like regular wine in sauce recipes.

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Specifically for Marsala I have found some recipes calling for the following substitutes:

¼ cup white grape juice

2 tablespoons sherry vinegar

1-tablespoon nonalcoholic vanilla extract

As said, I would replace the grape juice in this recipe with non alcoholic wine for the optimal result.