When I make chicken and vegetable pot pies they sometimes come out tasting like vinnegar. I have tried everything but this still happens

Good suggestion, I would of never thought that chicken pot pie or just trying to make the dish could sour in a million years. I make it a lot in the fall/winter, its my husbands favorite dish. My first home cook thought was that maybe the vessel or dish itself was compromised. There's nothing acidic to make it taste that way; I would have never thought of the stock/broth itself. Simone - I hope, you try again to maintain your rep!

Stock can sour. Joy of Cooking recommends when making stock to start with cold water and ingredients, bringing to the boil UNcovered, reducing to a simmer immediately after reaching the boil and simmer only partially, not fully, covered, then cooling uncovered. Somewhere along the line I've learned that cooling it covered can sour the stock. Then refrigerate, covered (and with its fat layer) up to 3-4 days. Since the authors also add that starchy vegetables can sour a stock, I wonder if the way or timing of the cornstarch thickener is affecting the last portion of the stock you are adding to the pies?

Post the recipe you're using for troubleshooting.