Watching a chef always intrigues me, as I see the kitchen as a place for change. I see each move being made and I watch carefully analyzing each step. I am not a cook, I am often a voyeur, I enjoy the act and not the action.
The idea of cooking grape leaves or stuffing onions and slow cooking is a good idea but the heat at the bottom will eventually become a glue to the pot unless you do something about it. As the water evaporates and the leaves begin to make direct contact with the bottom of the pot the sugars develop into a sweet and sticky glue.
Water is such a convenient lubricant and solvent in cooking because it doesn’t burn and two principal factors determine whether or not a sauce or puree will burn: the thickness of the liquid and the temperature of the pot.
In a pot of thin liquid, hotter fluid at the bottom of the pan can rise rapidly toward the surface, which pushes cooler parts of the food down in turbulent cycles of convection. A thin liquid, in other words, largely stirs itself.
A thick liquid behaves differently, for two reasons. First, concentrated sugars and other solids in the sauce increase the boiling point of the liquid and can burn. Heavier sauce is so slower as the mass is greater and hot spots begin to form on the bottom as the small bubbles of steam form at the bottom and aren’t buoyant enough to rise to the surface.
The part of the sauce near the pan bottom grows increasingly superheated until the small bubbles become so numerous that they form into solid columns of steam leading to “bubble explosions” like in a volcano.
The best way to avoid burning the dish is to add a layer at the bottom to insulate and maintain a low temperature and stir often to reduce the chances of burning the sauce.
Simmer at 95ºC and not much more or you’ll boil the water resulting in sugars from the vegetables forming and burning. The key to remember is that bubbles are tiny pockets of air trapped and as the steam inflated and disperses as bubbles breaking away. Trapping their movements without proper control will result in overcooking or burning so think about it next time you make a slow cooked dish.