STEM Tuesday: I’ll have onions with that

Onions on a neutral, mostly white background
Onions on a neutral, mostly white background (Photo credit: Wikipedia)

One of my favorite books is The Science of Cookingby Editors of Cook’s Illustrated and Guy Crosby, PhD.  Loved-One got it for me for Christmas.  I love that he appreciates my nerdiness.

Here’s some interesting things about onions.

You know how recipes tell you to mince, chop, slice, dice, julienne onions?  [tweetthis]Different ways of cutting an onion actually make them taste different. [/tweetthis] As the knife blade cuts through an onion, cells get ruptured. (I bet the first thing you looked at under a microscope was an onion. What? You never looked under a microscope? )

The intense flavor in an onion happens when alliinases, an enzyme in the cell wall, react with an  isoalliin, inside the cell creating thiosulfinates. These two chemicals come in contact when onion cells rupture during cutting. If you’ve ever cooked onions whole, like those little baby onions with stew, or roasted ones in the oven, you probably remember how sweet an onion can be.  Ummm… roasted with butter…. a carmelly delight.  Almost like a desert.

Cutting from “pole to pole” lessons the strong flavor, because fewer cells get ruptured. Usually, I cut across the equator, and slice away. That gives more intensity to the flavor.

Onions have a more complex, sweeter flavor if you cook them slowly. The onion actually has a variety of sulfur molecules that make up those thiosulfinates you created when you cut the onion. The heat breaks the molecules apart into disulfides and trisulfines, which taste sweet. The longer the onion is exposed to heat, the more diverse and interesting the taste. Heat to high? The enzyme gets deactivated, and the complexity of flavor gets lost. Oh and use butter or oil.  Gotta love what the Maillard reaction does to the taste of everything. If you want to know more about the Maillard reaction, click “Talking Turkey about Diabetes and the Maillard Reaction.”

Remember osmosis?  Salting the onion as soon as it goes in the sauté pan causes the water to move from inside the onion’s cells to the pan. That helps the Maillard reaction along.  Bottom line, a nice, brown, crunchy onion, with lots of flavor.

Do onions make you cry? [tweetthis]Did you ever notice that onions have next to no odor until you cut them.[/tweetthis] Another enzyme, LF synthase. This enzyme reacts to with sulfur containing molecules to create sulfuric propanethial S-oxide.  It makes people cry. The best way to protect against crying is to wear contact lenses. The next best thing is to light a candle.  Yup.  The flame changes the activity of sulfuric propanethial S-oxide by completely oxidizing it and probably deteriorating it as well.

Okay, enough chemistry.  Here’s a recipe I love. I got this from a young pregnant woman, Miss Z, a little over 16 years ago.  I was CeCe’s birth coach.  I met Miss Z when we all took the child-birth classes together.  I never liked beets before Miss Z taught me how to cook them like this.

CDC beets
CDC beets (Photo credit: Wikipedia)

Onions and Beets

What you need:

  • Water
  • Fresh washed beets with the green part cut off. (Do not peel)
  • Onion
  • Butter or Extra-virgin Olive Oil
  • Salt and Pepper


  1. Put the beets in a pan with about 1 inch of water.  Bring to a boil, then cover, simmer gently until fork punctures the beets easily.  Keep an eye on the water level, add more if needed;
  2. Cool beets until they are easy to handle.  Once they are cooled the skins will slide off the a slippery piece of
  3. Slice the onion finely (pole to pole)
  4. Cook in butter or oil on medium heat until onion is translucent.
  5. Slice up the beets and add to onion mixture.
  6. Add salt and pepper to taste

This dish will be quite sweet and tastey.  The beets lose some of their earthy flavor.  If you have a variety of sizes of beets, put the small ones on top; more heat will reach the bigger beets.

I purposely didn’t give you amounts because it really doesn’t matter. You can change the ratio of all of the ingredients, and it still tastes great.

Just don’t burn the beets.  That will create a chemical reaction that open windows, kitchen fans, and  Frebreze will have a hard time conquering.