Shocking food science explained (2024)

Dr. Seuss fans may be fine with green eggs and ham, but in our own kitchens chemical reactions can create some startling and off-putting effects. If you've ever had red onions go blue, carrots produce sparks or tomato-based foods "eat" aluminum foil, read on.

Red onions turn blue

A magazine article about red onions that turned blue in a frittata reminded me of a morning when as a child I was dawdling over breakfast and noticed that where the grape jelly touched it, the white of my fried egg had turned bluish green. I'm sure my mom explained that it was harmless, but for me it was the perfect excuse not to finish my breakfast.

The article – in Cook's Illustrated (April 2012) – was in response to a reader's question about why the red onions in his frittata had turned bluish green.

It explained that red produce, including onions, cabbage, cherries (and, I'm guessing the grapes in jelly) contain pigments called anthocyanins (cyan = blue). When they are cooked with acids their color intensifies, but when combined with an alkaline ingredient they can turn bluish green. Eggs, especially the whites, are alkaline – with a pH of 7.6 to 9.5 – and are most likely responsible for the blue-green color of the onions (and my fried egg white).

The staff at Cook's decided to see if they could reverse the color change once a fruit or vegetable turns blue. They sautéed red cabbage then added a pinch of baking soda to turn it blue. A splash of vinegar brought its red color back.

"This trick may not have a practical application," they said, "but it might impress your friends."

Sparking carrots

A reader wrote to Martha Stewart Living (July 2012) to ask why cooked diced carrots spark when she reheats them in the microwave. As many of you know, I use my microwave oven as little as possible – this just gives me one more excuse.

The answer came from Mark Morgan, professor of food engineering at Purdue University. Here's the condensed version.

Chopping mineral-rich vegetables into small pieces and heating them close together increases the likelihood of sparks due to variations in the electric field created by the microwaves.

The sparks don't harm the food but may prevent it from cooking evenly and leave a mark or burned taste. And if the food is very dry it might actually catch fire.

Robert Wolke, in his "What Einstein Told His Cook," explains that this is most likely to happen to carrots, because they are cut in cubes with corners, which act like the tip of a lightning rod, attracting electrical energy toward itself. The highly concentrated energy makes the sparks.

Black spots

I have used aluminum foil to wrap or cover foods made with tomatoes or tomato sauce only to find in a few days that some of the foil appears to have been eaten away or dissolved, leaving unappetizing black spots on the food.

According to the Reynolds Kitchens, this occurs when aluminum foil comes in contact with a food that is highly salted or acidic. The result of this reaction is an aluminum salt, which can be removed to improve the appearance of the food, but is harmless if eaten.

When aluminum comes in contact with another metal in the presence of moisture, an electrolytic reaction may occur, breaking down the aluminum. To avoid this, use glass, ceramic, plastic or paper containers. Do not cover sterling silver, silver plate or stainless steel with aluminum foil.

The color of meat

Why is packaged ground beef bright red on the outside and dark on the inside?

This question is answered by a USDA factsheet at

When meat is fresh and protected from contact with air (such as in vacuum packages), it has the purple-red color that comes from muscle protein or myoglobin.

When exposed to air, myoglobin forms oxymyoglobin, which gives beef a cherry-red color. The plastic wrap that allows oxygen to pass through it helps ensure that the surface of beef will retain this bright red color..

Exposure to store lighting as well as the continued contact with oxygen causes meat to turn brownish red. This color change alone does not mean the meat has spoiled. However, if the meat has an off odor or is sticky, tacky or slimy it should not be used.

But what about rainbow-colored sheen on some meats?

The USDA fact sheet explains that the iron, fat and other compounds in meat can create a rainbow effect when light hits them. And certain pigments in meats can give it an iridescent cast when exposed to heat and processing. Iridescence does not represent decreased quality or safety of the meat, according to the USDA.

Research for the National Cattlemen's Beef Association ( says that the structure of muscle fibers, hydration level of the meat, light conditions, angle of observation and angle at which the meat is cut all contribute to the effect.

Green yolks

I knew that plunging a hard-cooked egg into ice water as soon as it finished cooking could help prevent the yolk from turning green, but hadn't bothered to find out why. At, I found this simple explanation.

The longer you cook an egg, the more likely it is to form a green coating on the yolk. Submerging an egg in ice water immediately stops the cooking.

The green-gray color (and the whiff of sulfur smell that often accompanies it) comes from the reaction of iron in the egg yolk and sulfur in the egg white. When heated, the two can combine to make green-gray ferrous sulfide and hydrogen sulfide gas. To avoid getting a green yolk, cook eggs just long enough to reach the desired doneness – no more.


For summer picnics, it is nice to have a salad that will be crispy and fresh even if you make it the day before you serve it. With that in mind, the folks at America's Test Kitchen tweaked a popular layered salad and came up with this.



For the salad:

1 medium head iceberg lettuce, cored and roughly chopped (about 6 cups)

1 teaspoon salt

1/2 medium red onion thinly sliced

6 hard-cooked eggs, peeled and coarsely chopped

1 1/2 cups frozen peas

4 celery ribs thinly sliced

1 red bell pepper, stemmed, seeded and chopped

1 cucumber, halved lengthwise, seeded, and thinly sliced

1 pound bacon, cooked and crumbled

1 1/2 cups crumbled blue cheese

For the dressing:

1 1/2 cups mayonnaise

3 tablespoons cider vinegar

2 tablespoons hot sauce (see note)

2 teaspoons sugar

1 1/2 teaspoons pepper

Method: If you have one, a straight-sided clear glass serving bowl shows off the layers of this salad nicely. Place half the lettuce in bowl and sprinkle with 1/2 teaspoon salt. Rinse sliced onion under cold water and pat dry with paper towels. Layer onion, eggs, peas, celery, bell pepper and cucumber over lettuce. Add remaining lettuce and sprinkle with 1/2 teaspoon salt. Top with bacon and cheese.

For the dressing: Combine ingredients and spread evenly completely covering the top of the salad. Cover with plastic wrap and refrigerate for at least 8 and up to 24 hours. To serve, remove plastic wrap and toss until evenly coated with dressing.

E-mail Or write Linda Brandt, Sarasota Herald-Tribune, P.O. Drawer 1719, Sarasota, FL 34260.

Shocking food science explained (2024)


Top Articles
Latest Posts
Article information

Author: Kareem Mueller DO

Last Updated:

Views: 6320

Rating: 4.6 / 5 (66 voted)

Reviews: 89% of readers found this page helpful

Author information

Name: Kareem Mueller DO

Birthday: 1997-01-04

Address: Apt. 156 12935 Runolfsdottir Mission, Greenfort, MN 74384-6749

Phone: +16704982844747

Job: Corporate Administration Planner

Hobby: Mountain biking, Jewelry making, Stone skipping, Lacemaking, Knife making, Scrapbooking, Letterboxing

Introduction: My name is Kareem Mueller DO, I am a vivacious, super, thoughtful, excited, handsome, beautiful, combative person who loves writing and wants to share my knowledge and understanding with you.