For personal reasons I won't purchase alcohol or have it in my home, but I'm a bit of a foodie and love Chicken and Steak Marsala. I've found decent nonalcoholic substitutes for dry and sweet white wines and burgundy (Meiers Sparkling Juice), which covers most of the recipes I've wanted to make, but I've never found a good substitute for Marsala. Are there any non-alcoholic versions that would pass in a recipe, or a decent mix of other juices or ingredients that would pass, even if I have to process it somehow?
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.
It's very difficult to replace Marsala - it has plenty of flavors.
There is a fair chance that you like a specific flavor within the Marsala, which is the important distinction you desire.
The flavors of Marsala are often describes as walnut, curry plant (Helichrysum italicum - not to be confused with curry leaves), chocolate, leather, honey and dates, together with a distinct acidity and saltiness.
So, if you want to recreate the flavor, you have to experiment with these flavors, instead of "doing something with grapes". The most difficult part of course is leather.
I would try long-brewed green tea, which will end up with a lot of tannin - this is the bitterness and astringency you need. Together with dark chocolate, honey, salt and wine vinegar for the acidity, you could, in theory, create something similar.
If you want to cheat, you can just get Marsala flavoring, f.e.: http://www.bickfordflavors.com/products/marsala-flavor
You may be able to mix a sugar syrup with balsamic vinegar to get a similar effect.
You can take white sugar and mix it with as little boiling water as possible to make it all dissolve, and then add a bit of Balsamic. I'm not sure of exact quantities, but you can add a bit, taste, and then correct as needed.
It isn't a perfect substitute, but should work well for a cooked dish.