The Food Lab: Better Home Cooking Through Science

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
lost 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