I cooked a vegetable stew (onions, carrots, cabbage, potatoes) in a dutch oven on the stovetop for about 30-40 minutes on medium heat. The food turned out fine, but there's a thick layer of black residue in the bottom of the dutch oven when I'm done cooking (which I am able to clean off). Is this the burned sugars from within the veggies? Is there a better way to cook for a long time with a dutch oven on a stovetop without leaving blackened residue on the bottom?
From my experience, I believe it to be the sugars and proteins in whatever liquid you're cooking in that is what's actually burning, and not the vegetables themselves.
You can try a few things:
- As @myklbykl mentioned, stir frequently. I typically aim for every 15 minutes, but my stews typically take more than an hour, not 30-40 minutes. For yours, you might want to aim for every 5-10 minutes. I also like a spatula, as the flat end helps you to make sure that you're scraping the bottom well. (but I use wood, not silicone)
- Turn the heat down. You don't actually want to see the stew vigorously bubbling. You typically want to see an occassional bubble, which for most stoves, if you have a well-fit lid is low or warm, not 'medium'.
- Move the pot to the oven. I know you said wanted to do it on the stove-top, but the more even heat means that you can keep the oven pretty low and not have the temperature gradient that you would by cooking it on the stove.
- Add your potatoes later. If they're breaking down on you, this will thicken the liquid and make it more likely to burn. Instead, cut them smaller and add them later.
- Change your potatoes. Again, if they're breaking up on your, change to a 'waxy' (roasting) potato instead of a 'floury' (baking) potato. If the stew still isn't thick enough for your liking five minutes before serving, take a box grater and grate a potato straight into the stew ... it'll act like instant mashed potatoes and thicken up quickly.