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 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.
According to America's Test Kitchen extensive testing, tomatoes/wine/vinegar are fine as long as your cast iron is well-seasoned and you do not leave the acidic dish in it for an extended period (including cleaning the pan right after you finish cooking). They found that the slight acidity of tomatoes was enough to cause metallic flavor after thirty minutes.
You should not use cast iron for this particular recipe because the required hours of cooking and higher acidity of wine/vinegar will cause much more metallic flavor than the 30-min tomato example.
If you used cast iron anyway in this case, you'd probably have to toss the brisket for tasting too metallic and need to redo your seasoning. Worst case, the acid would cause a pitted surface in the cast iron, which can make it difficult to get a good even layer of seasoning. Even that doesn't totally ruin the cookware though. This Redditor soaked their cast iron for weeks in a 50-50 mix of water+vinegar without realizing the risks, and didn't notice anything besides some pitting. The replies link to this article and this YouTube video, which show that severe pitting doesn't prevent a perfect seasoning, just makes it a bit more work.
I suggest that if you're concerned about a particular recipe being too acidic for too long, try simply tasting the food every 10 minutes (assuming it's safe to eat without being fully cooked). If it starts tasting too metallic, then you know the recipe is not a good fit and you can stop before damaging the seasoning or worse.