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Metro Science: Eggnog chemistry, fish screams and why coal is the best present for kids

Your guide to the coolest science stories of Christmas.

Nothing says Christmas like that sweet, sweet combination of eggs, sugar, liquor and high-fat dairy — but what's the science behind eggnog?

OlafSpeier

Nothing says Christmas like that sweet, sweet combination of eggs, sugar, liquor and high-fat dairy — but what's the science behind eggnog?

Nothing says Christmas like that sweet, sweet combination of eggs, sugar, liquor and high-fat dairy, sometimes with a touch of vanilla and a dusting of nutmeg. Eggnog has some complex chemistry behind it. Here's the scientific magic behind your cup of Christmas cheer.

NOG KNOWLEDGE

Eggnog starts with milk. Homogenized milk contains tiny droplets of fat dispersed in a watery solution with disolved proteins called caseins.

Casein molecules form little globe shapes called micelles, and they love to clump together — a.k.a, curdle. Liquid milk doesn’t spontaneously curdle all the time in part because at the pH of milk, the micelles are negatively charged and repel each other. But if acid is added, positive ions strip off the negative ones, and the casein clumps.

The two keys to good eggnog are mixing all the ingredients together smoothly — a process called emulsification — and preventing casein from clumping, because no one likes chunky nog.

Liquors like brandy, bourbon and rum are rather acidic. Dump that directly into milk and it could be curdle city. But if you combine the egg yolks and sugar, gradually add the dairy and booze, and finally the whipped egg whites, your eggnog will stay creamy.

That’s because of lecithins, magic emulsifying molecules found in egg yolks. They have one end that is attracted to water and alcohol, and another that binds with fat. They hold the whole mixture together in happy harmony.

Choosing a high-fat mixture of milk and cream also helps. Fat globules help keep caseins away from each other. So put down that carton of skim. It’s the holidays!

Store-bought eggnog is different, it stays together thanks to thickeners such as carageenan.

Oh, and one final note: Raw eggs carry a risk of salmonella, especially for children, the elderly, and those with compromised immune systems. Pasteurized eggs are safe, or you can use a recipe that calls for cooking the eggs.

SCIENCE STORIES

Give the kids coal (or at least fewer toys!)

New research out of the University of Toledo suggests that the fewer toys children have around them, the higher the quality of play.

iStock

New research out of the University of Toledo suggests that the fewer toys children have around them, the higher the quality of play.

A shorter wish list might be a better wish list for the toddlers in your life. New research out of the University of Toledo published in the journal Infant Behavior and Development suggests that the fewer toys children have around them, the higher the quality of play. The small sample of kids in the study played with each toy longer and in a greater variety of ways.

FISH GET LOUD

Scientists have captured the loudest recorded sounds to ever come from fish.

Willard / iStock

Scientists have captured the loudest recorded sounds to ever come from fish.

Scientists have captured the loudest recorded sounds to ever come from fish. Mating Gulf corvina were taped at 150 decibels, the equivalent of hearing a jet engine from 7 metres.

SOUND SMART: Your science vocabulary word

DEFINITION: Milk is a colloid — a uniform mixture made of one substance evenly dispersed, but not dissolved, into another one.

USE IT IN A SENTENCE

Deborah and her besties are so close they practically form a colloid.

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