The food lab better home cooking through science ( PDFDrive ) 970

When you drop a green vegetable into a pot of boiling water, a number of changes occur First, blanching destroys enough cellular structure to just barely tenderize the vegetable to the point that it has lo st its raw, fibrous edge but still retains crunch Second, intercellular gases expand and escape from the vegetable (you’ll notice small bubbles coming out of, say, your asparagus stalks for a moment or two after dropping them into the hot water) This initial escape of gas is what causes the color of a vegetable to change from pale green to a vibrant bright green —the gas pockets that had been diffusing light suddenly disappear, allowing the full color of the chlorophyll pigment to stand out At the same time, enzymes that would naturally break green pigments down into brown ones are destroyed This is why blanched vegetables appear brighter green and, more important, stay bright green much longer than raw vegetables Of course, continue cooking too long, and the chlorophyll will eventually break down and your vegetables will go from bright green to a drab olive green or even brown The goal is to effect those changes as quickly as possible, without allowing time for the chlorophyll to begin breaking down That’s why you want to use plenty of water—it retains its temperature better after you add the vegetables, which subsequently cook faster.* Rule #2: Blanch Each Vegetable Separately ... vegetables Of course, continue cooking too long, and the chlorophyll will eventually break down and your vegetables will go from bright green to a drab olive green or even brown The goal is to effect... possible, without allowing time for the chlorophyll to begin breaking down That’s why you want to use plenty of water—it retains its temperature better after you add the vegetables, which subsequently cook faster.*