The beverages people consume every day are complex chemical systems known as mixtures. Nearly every drink, from a simple glass of flavored water to a creamy latte, is a combination of two or more substances that retain their individual chemical properties. These mixtures typically involve a solvent, which is usually water, and various solutes like sugars, acids, flavor compounds, and colorants. The science of how these components mix and remain together directly influences a drink’s taste, texture, and visual appearance.
The Simple Mixture: True Solutions
A true solution is characterized by its homogeneity and clarity. In these mixtures, the solute particles are dissolved at a molecular or ionic level, typically less than one nanometer in diameter. This minute size allows the solute to be completely dispersed within the solvent, creating a uniform blend that appears transparent.
Clear tea or standard carbonated water are examples of true solutions. The dissolved sugar molecules or carbon dioxide gas are too small to be seen, even under a microscope. Because the particles are fully dissolved, they cannot be filtered out using standard methods and will never separate or settle out over time. Filtered coffee and simple salt water also fall into this category.
Cloudy and Opaque: Colloids and Suspensions
Colloids and suspensions contain larger particles that lead to cloudiness or opacity, distinguished primarily by particle size. Colloids contain medium-sized particles (one to one thousand nanometers) that are large enough to scatter light but small enough to remain dispersed. This light-scattering property is known as the Tyndall effect, which makes a laser beam passed through milk or cloudy apple juice clearly visible.
Colloidal particles, such as fat globules in homogenized milk, are kept in motion by Brownian motion—constant collisions with water molecules—which prevents them from settling. Suspensions contain the largest particles, exceeding one thousand nanometers, which are visible to the naked eye. These particles are too heavy to be held up by molecular collisions. Pulpy orange juice or freshly mixed herbal teas are classic suspensions, requiring a “shake well” instruction because the fragments settle out due to gravity.
Textural Components: Emulsions and Foams
Emulsions and foams are common complex mixtures that create unique textures. An emulsion is a type of colloid where two liquids that normally do not mix, such as oil and water, are forced to disperse into one another. Cream liqueurs and many flavored soft drinks are oil-in-water emulsions, where tiny droplets of flavoring oil are suspended within the aqueous base.
These mixtures rely on emulsifiers, specialized molecules that bridge the oil and water phases, forming a protective barrier around the oil droplets to prevent merging. Foams are mixtures where a gas is dispersed throughout a liquid, creating texture through aeration. The head on a glass of beer is a protein-stabilized foam, where gas bubbles are trapped by proteins from the barley.
Maintaining the Mix: Factors Affecting Stability
The stability of a beverage mixture determines its shelf life and resistance to separation. Instability can manifest as sedimentation, where heavy particles fall to the bottom, or creaming, where less dense particles rise to the top. Flocculation (particles clumping together) and coalescence (particles merging completely) are related forms of instability that accelerate separation.
Physical factors such as temperature and pH level significantly influence stability by affecting the charge and structure of the dispersed particles. To counteract these forces, commercial beverages often contain stabilizers, typically hydrocolloids like xanthan gum or carrageenan. These ingredients work by increasing the viscosity of the liquid phase, slowing down the movement of dispersed particles and preventing them from settling or rising.