Why Steaming Your Broccoli is Faster than Roasting It

photo: Wikihow

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 ;-)

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  • Vic

    Is steaming healthier than roasting? I only lightly steam my vegies, just to the point where they’ve got just a slight bit of crunch to them.. not too soft. I think this makes it more bioavailable to the body without destroying the nutrition. Is my logic ok? Some vegies like broccoli are disgusting for me to eat raw, so I juice those.

    • Jason Harrison

      Nutritionfacts.org has a suggestion: cut/blend the broccoli as long as reasonably possible before cooking it. Mechanical stress causes the broccoli enzymes to create repair antioxidants. Cooking stops the process. By then steaming or roasting is probably the same.

  • Thatlibrarygeek

    But roasted broccoli is so yummy.

  • Catherine

    How interesting! Although I agree with Thatlibrarygeek, roasted is yummier. :)

  • Kat Eaton

    Our latest thing is lightly steaming, then searing in a hot skillet with a little olive oil, tamari & garlic. Ads more flavor like you get with roasted, but a little faster. I also feel like they stay more moist when steamed. (unless you toss with enough oil when roasting).