Mayonnaise and hollandaise are both oil-in-water culinary emulsions: droplets of oil dispersed through an aqueous phase. Their stability depends on physical forces at the oil–water interface and on molecules that concentrate at that interface to prevent droplets from merging. Emulsion science explains how interfacial chemistry, droplet size and the continuous phase’s properties combine to produce a spreadable emulsion or a warm, pourable sauce. David J. McClements, University of Massachusetts Amherst, outlines these core mechanisms in his reviews on food colloids and emulsions.
How emulsifiers and proteins act at the interface
The most important stabilizers in these sauces are surface-active molecules. In egg yolk, lecithin is a phospholipid that preferentially adsorbs at the oil–water boundary, reducing interfacial tension and allowing small droplets to form under shear. Egg yolk also contains proteins that unfold and form a viscoelastic film around droplets; that film resists coalescence by creating a mechanical barrier. Paul Walstra, Wageningen University & Research, describes how combined phospholipid–protein layers are particularly effective because the phospholipids lower tension quickly while proteins form stronger, more elastic layers over time.
Droplet size matters because smaller droplets have less tendency to coalesce and cream under gravity. Mechanical action during whisking or blending breaks oil into droplets; rapid adsorption of emulsifiers and proteins locks them in. The viscosity of the continuous aqueous phase further slows droplet movement, so thicker mayonnaises resist separation better than thin ones. These principles are summarized in standard texts on food colloids and were emphasized by David J. McClements in his textbooks and reviews.
Mechanical, chemical and thermal influences on stability
The two sauces differ in how they are made and in the stresses they face. Mayonnaise is assembled cold with vigorous shearing, creating many small droplets stabilized by lecithin-rich yolk and proteins. Hollandaise is an emulsion formed with warm butter and tempered egg yolks; heat partially denatures yolk proteins so they can more effectively form a film, but excessive heat causes irreversible coagulation and collapse of the emulsion. Practical culinary guidance and the underlying protein chemistry are discussed by food scientists and culinary researchers, including McClements, who links thermal denaturation to changes in interfacial properties.
Acidity and salt also influence stability: acid in hollandaise both flavors and changes protein charge, which affects how proteins spread and interact at the interface. Oil composition influences texture and flavor, and has environmental consequences: the choice of oils such as olive, canola, or palm impacts regional cuisines and has different sustainability profiles that matter to producers and consumers.
Consequences of destabilization are familiar in the kitchen: broken sauces show oil pooling or curdled textures because droplets have coalesced or proteins have aggregated. Understanding the competing roles of emulsifier adsorption, interfacial film strength, droplet size, and continuous-phase viscosity makes it possible to control stability—by adjusting whisking, temperature, acidity, or emulsifier concentration—guided by both scientific literature and culinary practice.