Mayonnaise is such a fun thing to eat - it goes with bread, chapattis, burgers, pizzas, everything. How does it stay creamy all the time - even though it keeps going in and out of the fridge?
If you keep jam in the fridge, it becomes quite hard. Then you have to let it be warm till it is runny enough to spread. But mayonnaise ('mayo' for short) stays the same throughout. The reason is emulsifiers.
Mayo is made from oil and eggs beaten together. To which you can add spices, herbs. The yolk of the egg contains a protein called lecithin. Lecithin acts a bit like soap. It helps the water in the egg white mix with the oil, so you get a uniform creamy liquid. The oil stops the water and egg proteins from forming crystals, so that even if you put it in the freezer, mayo will stay creamy.
Anything that helps water and oil mix is called an emulsifier. Therefore, lecithin is an emulsifier too. Even soap is an emulsifier. It helps break up the grease stain on your clothes into tiny drops that mix with the washing water. You can also use mustard and honey as good emulsifiers when making home-made jams and pickles.
Practically any packaged food you buy from the supermarket has emulsifiers in it. Next time you go to one, check out the packets of butter, cheese, sauce, yoghurt etc. The emulsifiers in them help them stay intact, or else the oily and non-oily components will separate.
The Mayo Experiment
Try making some mayo at home, with help from your parents. Take two bowls and put a few tablespoonfuls of cooking oil in each. Squeeze some lemon juice in each (or you can add a spoonful of vinegar). Now in one bowl, break an egg and add it whole. In the other bowl, add only the while of the egg, leaving the yolk out.
Beat the egg-and-oil mixture till the mayo is ready. Now wait for sometime and see what happens. Did the oil and egg white separate in the bowl where the yolk was not added? Did the mayo you made with yolk stay intact?
(After you've tried out your experiment, just add the yolk back into the mayo and whisk it again. That way, you'll have done good science, and made some tasty food too!)