Science At The Christmas BBQ ! - GoKids - Connect and Learn through daily fun interactions!

Hi kids, let's have a bit of fun at the Christmas BBQ this year, and learn something interesting as well – What happens when you mix oil and water ?

You will need:

For the vinaigrette

1/3 cup olive oil
1/4 cup balsamic vinegar
salt, pepper to taste
1 clove of garlic (optional)
1 teaspoon of maple syrup (optional)

For the mayonnaise

3 egg yolks
2 teaspoons Dijon mustard
150ml olive oil
150ml sunflower oil
2 tablespoons lemon juice

Equipment

Sealed jar
Measuring jug
Mixing bowl
Tea towel
Tablespoon

What to do

First make the vinaigrette.

1. Combine all the vinaigrette ingredients in the jar, and take note of the separation between the oil and vinegar.

2. Seal the container well and shake.

3. Let the mixture sit for a while and observe what happens to the vinegar and oil.

4. Shake the mixture again to combine the ingredients.

Next, prepare the mayonnaise.

1. Combine the two oils in a measuring jug. You will have 300ml of oil. As a general rule of thumb, the ratio is 100ml oil to 1 egg yolk.

2. Place a bowl on a damp tea towel (this helps to stabilise the bowl while whisking), add egg yolks, mustard and the lemon juice. Stir to combine.

3. Slowly add combined oils to egg yolk mixture, drop by drop at first while you keep whisking, then pour the oil in a thin steady stream, whisking continuously, until mayonnaise is thick and well combined.

4. Add more lemon juice or white wine vinegar to taste and whisk until combined, then season to taste with salt and black pepper.

5. Mayonnaise will keep for a week in the fridge. Cover with plastic wrap or in an airtight container.

Try adding other flavourings, such as chopped chives or garlic, if you like. Do what all good scientists and chefs do – experiment!

Your vinaigrette will be great on any green salad and the mayonnaise is perfect for a yummy potato salad.

Two liquids cannot be mixed together into a solution are called immiscible.

When shaken, the oil and vinegar seemed to mix but when the contents were allowed to sit, the two liquids formed two separate layers.

What’s happening?

When you made the vinaigrette, you will have noticed that it is impossible for oil and vinegar to mix together. They are called immiscible, meaning the two liquids cannot be mixed together into a solution. When shaken, the oil and vinegar seemed to mix but when the contents were allowed to sit, the two liquids formed two separate layers. Eventually, the oil droplets enlarge to become a separate layer on top of the vinegar.

This phenomenon is called coalescence, and happens when small droplets recombine to form bigger ones.The oil is on the top layer because it is less dense than the vinegar. Vinegar is denser than oil as it is made up mostly of water – it is a dilute solution of acetic acid. Water molecules like to stick together. That’s why water drops bead up when you spray them on a waxy surface and it’s also part of the reason why oil and water don’t mix. Homemade oil and vinegar salad dressing (vinaigrette) is an unstable mixture that will quickly separate unless shaken continuously. Mayonnaise uses an egg yolk to emulsify vinegar or lemon juice with oil. Egg yolk contains lecithin which helps form the mayonnaise emulsion. The egg yolk emulsifier acts as a bridge between both the oil and the water, allowing the oil to mix and break down into tiny drops that won’t reform. This means it is not a solution. A solution is made when two or more liquids are totally mixed together. Because the oil is still separate from the vinegar, even with the egg yolk present, it cannot be a solution.

The homogenised milk that we buy from the shop is made this way. Milk from the cow naturally separates into cream (oil based) on top and skim milk (water based) on the bottom. Before milk is bottled, it is squirted through a sieve at high speed. This breaks down the two liquids into tiny drops suspended in another liquid that won’t separate. Any mix of two liquids similar to this is called an emulsion.

Mayonnaise uses an egg yolk to emulsify vinegar or lemon juice with oil.

Applications

Mayonnaise that you buy at the shop labelled "real mayonnaise" only uses egg as an emulsifier. Reduced fat mayonnaise, which isn't considered “real” mayonnaise, usually contains modified food starch, cellulose gel and other thickeners and emulsifiers.Artists also use egg yolk as an emulsifier in tempera paint, to hold the various ingredients together.

An emulsion consists of millions of tiny droplets of one liquid suspended inside another liquid. Oil based paint is another emulsion as are many medicines and cosmetics. They are mixes of oils and water-based substances, held together by an emulsifier.