The Science of Emulsification: Homemade Mayonnaise Tutorial | Martha Stewart

Mayonnaise is an emulsion sauce that combines oil and water phases, stabilized by lecithin in egg yolk which acts as a surfactant to prevent the oil droplets from coalescing; when mayonnaise breaks (separates into oil and water), it can be fixed by adding water to increase the aqueous phase and re-emulsifying the mixture.

Mayonnaise is an oil-in-water emulsion stabilized by lecithin, which remains intact even when the emulsion breaks; to restore broken mayonnaise, add a small amount of very cold water to the bottom of the container and slowly beat the mixture while gradually reintroducing the broken mayonnaise, which allows the lecithin to re-emulsify the oil and water.

When mayonnaise breaks (separates), there are two options: start over from scratch, or rescue it. To rescue, place the broken mayonnaise in a bowl, add one whole egg to a blender, and blend at low speed. Slowly add the broken mayonnaise like oil, gradually incorporating it to re-emulsify the mixture.

Mayonnaise is an emulsion created by slowly incorporating oil into egg yolk, which acts as an emulsifier to disperse oil droplets and bind them with water from vinegar; if oil is added too quickly, the emulsion breaks and the mayonnaise separates, but this can be fixed by adding warm water and beating rapidly to re-emulsify the mixture.

This segment demonstrates how to recover broken mayonnaise when the emulsion separates. The instructor intentionally breaks the mayonnaise to show the recovery process. To fix broken mayonnaise, add 2 eggs and lemon juice to the broken mixture, then blend again. The instructor explains that breaking occurs when the emulsion separates, usually due to improper technique or lack of focus. This technique allows saving and reusing broken mayonnaise without waste, which is particularly valuable for businesses.

Hollandaise sauce is an emulsion created by egg yolk acting as an emulsifier that binds melted butter and lemon juice together; the sauce requires precise temperature control between 55-60°C because below 55°C the egg yolk cannot create a stable emulsion, while above 62°C the egg proteins coagulate and cause the sauce to curdle into scrambled eggs.

Hollandaise and Bearnaise represent the emulsion category of mother sauces, relying on delicate chemical processes to combine fat and liquid. Hollandaise is created by whisking egg yolks over a bain-marie until reaching approximately 74°C, then slowly incorporating clarified butter while continuously whisking. Vinegar provides acidity and stability; water prevents curdling. Bearnaise adds tarragon and chives to hollandaise for a distinctive flavor profile. Both sauces pair excellently with steak. The video explains that salt inhibits emulsion formation by binding to protein particles, so it's typically added at the end. These sauces demonstrate how precise temperature control and continuous movement maintain complex molecular structures that give them their characteristic richness and stability.

Hollandaise sauce represents the emulsion-based category, using butter and egg yolks as the thickener—essentially hot mayonnaise. Preparation requires reducing wine and vinegar with shallot and peppercorns, then carefully incorporating egg yolks while whisking constantly between heat and off heat until they triple in volume. Melted butter at 145°F is then slowly incorporated. Temperature control is critical to prevent scrambling eggs. The sauce thickens further upon cooling. Common derivatives include Bearnaise (Hollandaise + tarragon/chervil). Applications include eggs Benedict and steak Oscar.

Hollandaise sauce is an emulsified butter sauce where egg yolks act as natural emulsifiers (containing lecithin and phospholipids) that bridge water-loving and water-repelling compounds to suspend butter in a stable mixture; the sauce can be made by either hand-whisking over a double boiler or blending, though hand-whisking provides better temperature control for maintaining the emulsion, and if the sauce breaks, adding water or lemon juice can restore it by increasing the continuous water phase.

When making béarnaise sauce, the pan must be very hot to properly emulsify the butter into the egg yolk mixture. If the pan is not hot enough, the sauce will not emulsify properly. However, if the pan is too hot, the eggs will coagulate and the sauce will curdle, turning into scrambled eggs. The sauce should begin to foam and increase in volume as it emulsifies. The whisk should be moved continuously and vigorously during this process.

Emulsification creates globules of one liquid dispersed in another immiscible liquid. The process involves two opposing forces: interfacial tension forces that resist globule deformation and breakup, and shear forces that promote deformation and breakup into smaller droplets. When shear forces exceed interfacial tension forces, globules deform and break down into smaller droplets. This balance determines final droplet size and emulsion stability. The process begins by adding oil to water, forming globules that are then mechanically broken down through continued shear action.

Emulsions form when interfacial tension between oil and water phases is reduced. The emulsifying agent reduces attractive forces between dispersed droplets, allowing them to remain dispersed. Mechanical energy (shear forces) breaks up the dispersed phase into small droplets. The balance between interfacial tension and shear forces determines droplet size and emulsion stability.

In emulsions (dispersions of two immiscible liquids), droplets deform and rotate under shear fields, with their shape and orientation governed by the capillary number (Ca = ηγ̇r/σ, the ratio of viscous to surface forces) and viscosity ratio (κ). At low Ca, surface tension dominates and droplets remain spherical; at intermediate Ca, droplets become ellipsoidal with ellipticity and orientation angle depending on κ. The orientation angle θ (measured from the perpendicular to flow direction) ranges from 45° for easily deformable droplets to 90° for droplets with high viscosity ratio, as described by Cox's 1968 fluid mechanics analysis.

An emulsion is a stable mixture of two immiscible liquids (like oil and water) achieved by adding an emulsifier (such as lecithin in egg yolks) and applying sufficient shear force during mixing; the shear breaks larger particles into smaller sizes, enabling the emulsifier to effectively bind the two phases together, as demonstrated by comparing low-shear blending (which produces an oily egg mixture) with high-shear blending (which creates smooth, stable mayonnaise).

Emulsions serve multiple applications: (1) Parenteral nutrition for delivering lipophilic nutrients; (2) Controlled release formulations using W/O emulsions; (3) Transdermal delivery using micro emulsions for better penetration. The choice depends on therapeutic goals, route of administration, and patient needs. Each application requires specific formulation considerations.

Pharmaceutical emulsions deliver poorly water-soluble drugs, mask bitter tastes, protect unstable drugs from oxidation/hydrolysis, and improve absorption. Intravenous emulsions deliver essential nutrients (carbohydrates, fats, vitamins) to bedridden patients. Industrial applications include making medicines more palatable, improving effectiveness through controlled dosing, and enhancing aesthetics for topical drugs. Disadvantages include thermodynamic instability requiring stabilization, manufacturing difficulties, bulkiness, transport challenges, microbial contamination risks, and potential dose inaccuracy.

Membrane emulsification is a drop-by-drop manufacturing technique that produces uniform microcapsules by forcing a dispersed phase through a metal membrane with precisely controlled pores, where capillary forces hold drops on the membrane surface until drag forces from applied shear cause detachment, enabling the production of particles with narrow size distributions (CV < 40%) suitable for pharmaceutical, cosmetic, and food applications including cell encapsulation and controlled release systems.

Emulsions are valuable for transdermal drug delivery where drugs are dispersed in the internal phase, protected from direct skin contact. Microemulsions are particularly effective for cancer drug delivery due to their small size and enhanced permeability through abnormal tumor blood vessels. For oral administration, emulsions improve drug absorption and bioavailability for lipophilic drugs. For topical applications, oil-in-water emulsions are used in lotions and creams for moisturizing effects, while water-in-oil emulsions with high oil content serve as protective barriers preventing moisture loss.

Emulsions play crucial roles in modern drug delivery systems. They are used for intravenous drug delivery, particularly in parenteral nutrition for delivering lipids to patients who cannot absorb nutrients through the gastrointestinal tract. Emulsions are also employed in topical applications like creams and lotions for skin protection and drug delivery. In rectal preparations such as suppositories and enemas, emulsions provide direct drug delivery to the rectal mucosa. For oral drug delivery, emulsions enhance the dissolution and absorption of poorly water-soluble drugs. Emulsions can be designed for controlled release formulations by modifying composition and particle size. In nanomedicine, nanoemulsions (particle size <100 nm) enable targeted drug delivery and controlled release. Emulsions also serve as pharmaceutical excipients for drug encapsulation, protecting unstable compounds and improving stability.