Mixing It Up - The Chemistry of Emulsions

Ever hear the saying "Oil and Water don't mix."? If you have ever cooked a turkey and had to pour off the fat to make a gravy or just tried to make a vinegar and oil dressing or wash greasy dishes with water alone, you have seen how this is true. Oils are lighter than water and are non-polar hydrocarbons so they generally float on top of the water or broth. But that does not mean you cannot get them to mix, you just need to know how. You have to use chemistry in the kitchen.

Oil and water don’t mix because oil is made up of non-polar molecules while water molecules are polar. You have to make an emulsion to combine them. An emulsion is a mixture of two liquids which normally cannot combine smoothly - oil and water being the classic example. One liquid (the dispersed phase) is dispersed in the other (the continuous phase). Oil and water can form Oil-in-Water and Water-in-Oil emulsions. Emulsifying is done by slowly adding one ingredient to another while at the same time mixing rapidly.

A. Two immiscible liquids, not yet emulsified (oil & water) B. An emulsion of Phase II dispersed in Phase I (oil-in-water) C. The unstable emulsion progressively separates D. The emulsifier (purple outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsion

This disperses and suspends minute droplets of the slowly added liquid throughout the other. Sometimes another ingredient is also added to aid in the mixing, an emulsifier.

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An Emulsion is a mixture of two or more liquids
that normally don't mix.

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An emulsifier is typically a chemical that has both polar and non-polar properties. Soap cleans by acting as an emulsifier. The fatty acids in soaps act as emulsifiers because they have a polar acid ligand at one end and a non-polar hydrocarbon chain on the other. The acid is hydrated by the water and pulls the non-polar oils with its hydrocarbon chain into solution. This results in a oil in water emulsion and allows the oil to be washed away with the water. Detergents are primarily surfactants, acting to break down the surface tension of water. They essentially work in a similar fashion to soaps by allowing the oils to be held in suspension and washed away with the rinse water.

Emulsions and emulsifiers are frequently used in foods. Mayonnaise, an uncooked combination of oil, egg yolks (as emulsifier) and vinegar or lemon juice, is one of the best-known food emulsions.

Some common Oil-in-Water emulsions found in food:

• Brewed Coffee – Coffee oil in Water
• Mayonnaise and Hollandaise sauce – Stabilized with Egg Yolks
• Vinaigrette – Vegetable oil in vinegar (usually unstable - shaken before use to create an emulsion)
• Homogenized Milk – Milk fat in water (stabilized with milk proteins)

These chemicals can act as emulsifiers in foods, having both a polar component and a non-polar chain.

• Lecithin – Phospholipids found in Egg Yolks and Soy Beans
• Mustard
• Proteins – Egg whites and milk proteins
• Fatty Acids – Butter
• Triglycerides – Cooking oils and fats

Emulsions are also frequently used in pharmaceuticals, personal care products and cosmetics. These are usually oil and water emulsions, varying between oil-in-water and water-in-oil depending on the desired result. Oil-in-water emulsions are usually liquids or creams and do not have an oily texture. Water-in-oil emulsions tend to be oily and are frequently thicker, as with an ointment. Many are topical dosage forms, to be used on the skin's surface, or used transdermally, ophthalmically, rectally or vaginally. Popular medicated emulsions include calamine lotion, cod liver oil, hydrocortisone cream and Vitamin A & D ointment.

Phopholipid emulsifier layers in aqueous solution An Oil-in-Water emulsion

The hypnotic and anesthetic Propofol®, recently popularized as the agent that caused Michael Jackson's death in 2009, is an intravenous emulsion. The manufacturers emulsify the lipid-soluble Propofol® in a mixture of water, soy oil, and egg lecithin. Since our blood is primarily water, making an oil-in-water emulsion of the drug allows it to mix easily with our blood as it is injected. Emulsions are even used to feed us intravenously. The intravenous preparation Intralipid® is a 20% intravenous fat emulsion administered as a source of calories and essential fatty acids for individuals on long term intravenous feedings. It is a sterile emulsion made from 20% soybean oil, 1.2% egg yolk phospholipids (lecithin) and water.

So oil and water can mix after all, when you have an emulsifying agent to suspend one inside the other. In our lives too, without something to cover our sins, we do not mingle well with the grace and mercy of God. But He has provided a way to do just that, in His Son. We only need to ask.

Matthew 27:34 (NIKJV) - "They gave Him sour wine mingled with gall to drink. But when He had tasted it, He would not drink."