I had the weirdest thing happen while making a beef stew last night. After I'd sauteed the onions, chucked in the beef and carrots etc, I poured in a cup of red wine and a cup of water, and the stew liquid turned a HORRIBLE yucky greenish-black with foam/scum on top. It tasted really odd, really musty with a strong taste of mushrooms (despite not having any 'shrooms in there). Was cooking it in an enamelled cast-iron pot, and there was greenish-black residue all along the edges of the stew on the beige enamel surface. YUCK!!! Had to pour the whole thing in a colander and rinse out the meat and veg with cold water before cooking again in a new lot of stock and wine, which put dinner back by nearly an hour.
The only thing I can think of that might have caused it was sprinkling about a teaspoon of soda bicarb on the beef before coating in flour. (I wanted to save an hour or so of stewing time, and soda bicarb acts as a tenderiser for meat, which I do all the time with no ill results with stirfries but have never tried in a stew before.) Soda bicarb can sometimes leave a bitter aftertaste if too much is used, but 1 teaspoon for 800g beef is very little. DH reckons the acidic wine probably reacted with the soda bicarb to form the bubbly foam, but that still doesn't explain the weird colour or taste.
Does anyone have any idea what might have happened? Or experienced something similar?