I want to cook a beef brisket, following a recipe that suggests baking it on a bed of onions and red wine, or red wine vinegar. I'd like to use a cast iron dutch oven, but am concerned about the interaction between the wine and the iron. I've read tomatoes and iron is not recommended, but what about wine or vinegar?
I'd like to refer you to my answer to the question about chili in cast iron, from which I'll summarize the relevant parts:
Typical cast iron corrodes at a pH lower than 4.3; pure white vinegar (5%) has a pH of 2.4 and wine is around 3.2 to 3.8. If you plan to use either of these in cast iron, you'd better make sure they are heavily diluted, otherwise you may actually ruin your pot in addition to getting a pretty hefty iron supplement with your meal.
Cast iron is still somewhat reactive at borderline pH ranges, i.e. tomato juice or sauce. It'll leach out about 5 mg of iron for every 3 oz / 88 mL of liquid for typical cooking times. The typical human needs to ingest significantly more than 45 mg over a period of several days to become toxic, so it's generally considered OK and even healthy to cook dilute tomato solutions in cast iron, but wine and vinegar are another story.
Don't fill your cast-iron cookware with wine or vinegar. A splash for sauce or deglazing is OK, but tossing a significant amount straight into the pan undiluted will ruin your cookware, and your health.
P.S. Note that enameled cast iron (Le Creuset, etc.) is less reactive; the specifics depend on the brand. If you have this type of cast iron, I suggest doing your homework before taking the risk.
My understanding is that you want to avoid all fairly acidic liquids in cast iron, out of concern that it will leach an undesirable amount of iron into the food and/or change the flavor or color of the food. A squeeze of lemon juice into a sauce? No problem. Braise for 30 minutes in a very acidic sauce? Not such a good idea. (Unless of course your Dutch oven is actually enameled cast iron, with the white interior - in which case none of this applies, go right ahead with your plan.)
I think the issue with acid in iron is less what it does to the food and more what it does to the pan. You've spent all that effort building up and maintaining that beautiful seasoning, and anything strongly acidic like tomatoes or vinegar will strip that off.
I just wanted to add -- this should probably include beer as well. A quick search showed the pH of common beers is under 4.0.
I started my beef braise with the beer marinade in my cast-iron, non-enameled dutch oven. It smelled kind of metallic. I searched for it and found this post and others that mention wine and tomatoes due to acidity, but did not mention beer. Well -- adding it now !!
From what I've read, enameled cookware came into vogue here when specialized recipes, like beef bourguignon, or burgundy(?), were brought here from abroad due to the occurance of the bad reaction raw cast iron had with the wine. People noticed that not only was the seasoning leached from the cookware, but that it wound up in the food and ruined the flavour.