You probably know that heat transfer is proportional to the difference in temperature between the food and the heat source and a couple of degrees can make a difference to your work. In fact, boiling water is very efficient because it moves chaotically conducting heat into the surface of the food three times faster than water a few degrees cooler. A rolling boil cooks fast because the turbulence lifts the hottest water up to the surface, drags colder water down toward the bottom of the pot, and accelerates the transfer of heat.
Now think of cooking one of the most loved greens on our globe spinach. What is the best way to extract color and cook it to your taste. First of many green vegetables are made of up microscopic air spaces circulating around the plants cells, there the carbon dioxide and oxygen thrives and is better known as transpiration.
This labyrinth of cells are the life of the plant! As sunshine passes into the plant’s surface, some are absorbed by cells and the balance reflects green. The chlorophyll’s light as it reflects gives the green color you see in raw spinach, beans, etc.
When you blanch or cook the spinach the cells collapse due to the heat of the water and the pigments reflect more with a vivid bright green. The idea of blanching is done immediately and with ease as long as you do not overcrowd the pot, and not too long or you can destroy the color by leaching the pigments.