I can speak to a couple things.
Pepper (black, red, cayenne) seems to get bitter when pressure cooked or water bath canned over a period of months, so season lightly for preservation.
Hot sauce, when I make a wings hot sauce with butter and mustard, both liquid, then add hot sauce....it's fine. If I cook the concoction the hot sauce gets MUCH hotter, so beware.
When I make beef bourginion (sp?), which I love, it is ALWAYS better the next day, or frozen and served later, the flavors meld, it's more wonderful everytime.
Most tomato dishes (lasagna, chili) are better the next day or frozen and reheated.
Green yellow and red peppers get a little bitter when overcooked, they are best added at the end. (I don't cook them before putting them on pizza.)
When I've made Cam Potatoes (sliced, coated in oil, sprinkled with spices, baked crisp) I've noticed that the paprika or the garlic gets a little bitter and maybe I should not have had as heavy of a hand in putting so much on them.
Hope that helps, Bliss