Last class we saw for ourselves that water and oil do not mix. This is due to the fact that water is polar and oil is non-polar. Water molecules form strong hydrogen bonds with each other and are not as attracted to non-polar oil molecules. Shunned, oil separates from water and remains as droplets or a slick at the water’s surface, where there is the least amount of interaction with water molecules.
I was curious about ways that the “like dissolves like” rule could be bent and found this video ( https://www.youtube.com/watch?v=tETrZUhqaQo ) about some of the emulsifiers used in cooking to combine oil and vinegar. Vinegar is a polar substance made mostly of water and will separate from oil only minutes after whisking. An emulsifying agent like lecithin (found in egg yolks) can prevent this separation so that oil remains dispersed and suspended in the vinegar. This makes for a tastier vinaigrette.
As the video explains, lecithin (like soap) has a hydrophilic end as well as a hydrophobic end. The hydrophobic end is compatible with non-polar oil molecules, while the hydrophilic end of lecithin is compatible with polar vinegar molecules. This allows lecithin to form a kind of shield around droplets of oil, which makes it unnecessary for them to flee to the vinegar’s surface or recombine with other oil droplets.
I remember seeing ‘soy lecithin’ on many food labels. Apparently it’s cheap, which boosts its popularity amongst food manufacturers in need of an emulsifier. Also, it probably doesn’t have as noticeable a taste as mustard or egg.