Sunday, October 6, 2013

Why Steaming Your Broccoli is Faster than Roasting It

There are many ways to prepare vegetables such as broccoli and cauliflower. One very popular method is roasting them in the oven, and another is steaming them.
Steaming takes 5-7 minutes. Roasting takes 15-20.

At first this may seem counter-intuitive. Steam is boiled water at 220 degrees Fahrenheit, but an oven can reach temperatures of 450 Fahrenheit, so it should prepare the broccoli faster, right?
Wrong. If you’ve ever steamed food in a covered saucepan and lifted the lid, you may have inadvertently placed your hand directly over the steam and been instantly scalded. But, when you open your oven door to overturn some roasting vegetable, you can comfortably have your hand halfway inside for 10 seconds without being burned.
How could this be?

To answer, we go back to basic chemistry and the wonderful property of water molecules called hydrogen bonds. The H2O molecule is shaped like a V:  at the bottom imagine the oxygen atom and at the top 2 hydrogen atoms. This shape creates a slight electrical polarity that means the oxygen atom will be attracting hydrogen atoms from OTHER water molecules. Water molecules like to hang out together.

These hydrogen bonds means it takes a lot of energy to separate water molecules from one another. For example: when turning water to steam. Water in its liquid form will absorb a lot of heat (energy) before it finally starts to vaporize (become steam). This is called latent heat of vaporization.
So when we heat water to its boiling point and we get the steam going, there’s a lot of energy in those in those vapor molecules. Once that vapor touches the broccoli floret, it condenses back to liquid form, releasing a boatload of energy (heat) onto the vegetable, much more energy than dry, hot air upon contact with a floret in a nearby oven.

And that’s why steaming is faster than roasting. Science class dismissed ;-)

No comments: