Something we all understand, hopefully, is that ANY form of cooking reduces nutritional value of foods. The longer you cook something the less nutrition is left.
So with that in mind, when I cook for my pets the meats and veggies I use are just about cooked. When i cook chicken i put it in a pan with cold water and bring it to the boil, i simmer for 5 mins, skim the fat, and drain it, saving the liquid (broth) I put the liquid back in the pan and add giblets and hearts, again boil for about 5 mins, and skim the gooy brown skum stuff, saving it along with the skimmed fat, drain and save the broth, next the veggies. Put the broth back in the pan and add the veggies, again boil for about 5-10 mins, drain, saving the broth. Put the broth back in the pan and cook the rice, barley or whatever grain you are using, and let it cook until the grains are cooked and most of the broth absorbed. When feeding I add an portion of the cooked foods, (chicken has been deboned) which have been mixed together, and 1-2 tablespoons of the fats and skimmed substances, i grind down eggshells and add 1 teaspoon per meal of the powder to the food. my pets thrive on that combination.
When I visited a pet food maker many years ago, i saw huge amounts of the different ingriedents thrown into large vats and boiled until they became a mush, all the ingredients where then ground down to even more mush, that what then heat dryed, powdered, mixed and molded (during this process the dyes. powders, and preservatives were added). It is my understanding that the process has not changed that much.
This is just another reason i don’t like to feed mass produced animal foods.