Having made stock and strained it, can the meat and vegetables boiled up in the stock be used for anything, or should they go in the bin?
I would dump them, with the caveat that some chefs reserve bones for making a second, lighter stock. I've only heard of this being done with Veal, so your mileage may vary.
I've also heard of people combining stock and chicken salad making by throwing a whole chicken in to the stock pot, then using the white meat for salad.
This offends me on many levels, but I'll just say that it probably makes for bad chicken salad, and also almost certainly makes for cloudy stock.
I actually Googled this myself because I was wondering about the same thing. Someone else also suggested pureeing the veggies and adding them to spaghetti sauce. http://vegetarian.betterrecipes.com/vegetable-puree-leftover-vegetables-after-making-vegetable-stock.html
While I agree with all the comments about the lack of flavor and palatable texture in the boiled vegetables, they do have value. If you’re trying to increase insoluble fiber in your diet, anything that you can purée them and add them to (like a creamy potato soup or spaghetti sauce as suggested above) will have that benefit . At most, the cellulose content of onions is reduced by about 15% from boiling. I’m not sure if the longer boiling time reduces it significantly more.
So when I make beef stock I use the pressure cooker technique 3 hours and then everything is mush. After everything is sieved I go through the mush carefully removing anything which could be bone and remaining sinew. I then add lots of fresh parsley basil tomato passata and a bulb of confit garlic a decent glug of decent olive oil, food processor for 1 minute and you have a passable if somewhat strangely textured bolognaise sauce.
If there's any flavor left in chicken meat on the bone, or much collagen left in the bones after stock making, I'd say it hasn't simmered long enough. The stock should be both flavorful and unctuous, which means the meat will be flavorless and the bones brittle. Overnight is great for this, at a very low temperature - but with aromatics added later.
If you boil your stock, the tiny orifices in the bones from where collagen leaches will be sealed off, and the result will be much thinner than it could otherwise be.
Made stock last night with chicken carcass and assorted vegetable and fruit peelings. Used an InstantPot for 2 hours at high pressure. Separated and saved the clear stock.
Looked at the remaining solids, and reached for the hand blender. Added water and pureed the lot, including the bones. Gave it another 15 minutes at high pressure in the InstantPot.
A thick, smooth, opaque, dark brown, strongly smelling paste came out. Picture a concentrated sauce, or a liquidy pate. Judging from the aroma, probably too much orange peel this time around :)