One of my challenges as a new bride in 1957 was learning how to cook fresh vegetables. Some recipes said to cover with cold water and some mentioned hot water. My mother told me that vegetables grown underground (now called root vegetables) get covered with cold water and vegetables that are grown above the ground get started in hot water.
According to Harold McGee, dean of American food-scientists, your mother was absolutely correct. McGee, author of On Food and Cooking: The Science and Lore of the Kitchen (Scribner, 2004, $40), explained that, as your mother told you, the vegetable kingdom can be divided into two realms: green vegetables and root vegetables.
Cooking the former simply entails softening their cell walls to make them more palatable and easier to digest. Because most green vegetables are small and/or thin, this doesn't take long. The quickest method is to bring water to boil, add the vegetables and cook until they are just tender.
Root vegetables contain a great deal of starch, which needs to be dissolved before most root vegetables can be eaten. The problem of cooking root vegetables is complicated by the fact that most of them are quite large.
As root vegetables cook, "It takes a while for the heat to penetrate, and the outside layer is exposed to the boiling water for much longer than the inside." The result is that the surface of the vegetable becomes flaky and mealy.
Happily, there is a solution, McGee said. "Starting root vegetables out in cold water and heating the outside layers gradually allows for what turns out to be a fairly complex process. The cell walls get reinforced and become more resistant to the effects of overcooking."
Erica Marcus writes for Newsday. E-mail your queries to email@example.com, or send them to Erica Marcus, Food /Part 2, Newsday, 235 Pinelawn Road, Melville, NY 11747-4250.