Agriculture and Food 7–12 · Years 9–10

Emulsifiers: keeping oil and vinegar mixed

Food Service and Catering

PracticalLow risk

The idea

Oil and water separate into layers after shaking, but an emulsifier such as egg yolk or mustard keeps oil droplets dispersed so the mixture stays uniform.

What you need

boiling tubes with bungs, 6
cooking oil (corn oil is easiest to see), 2 mL per tube
water or vinegar, 2 mL per tube
mustard powder, egg yolk, egg white, plain flour and sugar, a small spatula tip or 3 drops of each
disposable pipettes for the egg
stop clock, ruler graduated in millimetres

How to do it

Put 2 mL of oil and 2 mL of water in a tube, stopper it and shake for 10 seconds, not too hard.
Stand the tube and record the time until two clear layers form and the height of the clear oil layer at 1, 5 and 15 minutes.
Repeat with a small quantity of one test substance added before shaking: mustard powder, egg yolk, egg white, flour, sugar.
Shake every tube the same way and record the same measurements.
In the food room, make two small vinaigrettes, one with and one without mustard, and compare them after 15 minutes.

What you should see

Without an emulsifier the oil and water separate into two clear layers within minutes. Egg yolk and mustard keep the mixture cloudy and uniform; flour, sugar and egg white do not form an oil-and-water emulsion, and two separate layers can be seen, as the RSC notes state. The vinaigrette with mustard separates more slowly than the one without. The learner knows it worked when the plain oil and water tube separates clearly and the egg yolk tube does not.

What changes

What you change: substance added (none, mustard powder, egg yolk, egg white, flour, sugar)
What you measure: time to separation (s); clear oil layer height (mm) at 1, 5 and 15 minutes
What you keep the same: oil and water volumes
shaking time and strength
amount of test substance
temperature

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Shaking harder makes oil and water mix for good.
Any thick ingredient, such as flour, will stop an emulsion separating.
Mayonnaise is thick because of the egg white.

Safety card

Low riskLearners carry it out

Hazards

Salmonella from raw egg
oil spills make floors slippery

Controls

minimal handling of raw egg using disposable pipettes; tubes with raw egg are never tasted
wipe spills at once

Note

Food handling follows the FSANZ food safety standards (Standard 3.2.2) as explained on the FSANZ food temperature and thermometers page; check class allergy and anaphylaxis records before any food is prepared; the Food Technology Years 7–10 Syllabus reminds teachers that food allergies can cause anaphylaxis.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Food Technology Years 7–10 Syllabus (2019)FT5-3 FT5-4
Food Technology 7–10 Syllabus (2025), new syllabus, implementation from 2028FT5-USE-01
Australian Curriculum v9AC9TDE10K05

Sources

The pages the author read to write this activity.

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