Flavor Emulsions for Beverage and Bakery Applications: What Flavorists Need to Know

Editor’s note: The article below provides some basics about flavor emulsions as a form of flavors, which the Society of Flavor Chemists requires all certified flavorists to understand. Flavor emulsions are a type of flavor that is particularly important for beverage and bakery products. Every flavorist needs to know how to formulate flavor emulsions. Those who want to have complete mastery of this technique may consider a book titled Flavor Emulsion Technology published by Flavorist.com.

Please be advised to consult legal advisors regarding the weighting-agent limits and the BVO status. Also, the formula and processing values in the starting formula, use levels, and homogenizer settings are for illustration only.

1. Introduction

A flavor emulsion is a stable dispersion of an oil-soluble flavor in a water-based carrier. It lets the flavorist deliver essential oils, oleoresins and other water-insoluble materials into products that are mostly water, such as soft drinks, or into batters and doughs that need a flavor able to survive the oven.

Two product families share the name but are built for very different jobs:

• Beverage emulsions are fine, homogenized, often weighted concentrates. They are diluted several hundred times into a drink and must stay uniformly dispersed for months on a shelf. They provide flavor, cloud (opacity), or both.
• Bakery emulsions are thicker, gum-stabilized flavor preparations with little or no ethanol. They are used at fairly high levels in batters, doughs, icings and fillings, where their main job is to hold flavor through mixing and baking.

The flavorist working on either type has to think beyond the flavor profile. Physical chemistry, regulatory limits, processing equipment and the end user's process all shape the final formula. The sections below cover the beverage emulsion in depth, because it is the more technically demanding of the two, and then treat bakery emulsions on their own terms.

2. The science behind emulsions

An emulsion is a mixture of two immiscible liquids in which one (the dispersed or internal phase) is distributed as droplets through the other (the continuous or external phase). Flavor emulsions for beverage and bakery use are almost always oil-in-water (O/W): flavor oil droplets suspended in water, sugar syrup or a water/glycol mix.

Emulsions are thermodynamically unstable. Left alone, the oil and water will always separate in the end. The formulator's task is to make that separation so slow that it does not happen within the shelf life of the concentrate or the finished product. Stability is kinetic, not permanent.

Stokes' law

The rate at which a droplet rises (creams) or sinks (sediments) in a dilute emulsion is described by Stokes' law:

where v is the droplet velocity, g is gravitational acceleration, r is the droplet radius, ρd and ρc are the densities of the dispersed and continuous phases, and η is the viscosity of the continuous phase.

The equation gives the formulator three levers:

1. Reduce droplet size. Velocity depends on the square of the radius, so halving the droplet size cuts the separation rate by a factor of four. This is the reason for high-pressure homogenization.
2. Reduce the density difference. Citrus oils have a density near 0.84–0.85 g/mL. A typical soft drink at 10–12 °Brix is about 1.04 g/mL. Adding a weighting agent to the oil brings its density closer to that of the drink.
3. Increase viscosity. Thickening the continuous phase slows droplet movement. This works well in a concentrate or a bakery emulsion, but it is lost once a beverage emulsion is diluted into a thin drink.

How emulsions fail

• Creaming: droplets lighter than the continuous phase rise and concentrate at the top. In a bottled drink this shows up as a white or oily band at the liquid surface, called a ring or neck ring. Creaming is reversible by shaking if droplets have not merged.
• Sedimentation: droplets heavier than the continuous phase sink. This happens when an oil is over-weighted.
• Flocculation: droplets cluster together without losing their identity. Flocs behave like large particles and cream or settle much faster.
• Coalescence: droplets merge into larger ones. This is irreversible and leads to visible oil slicks or free oil.
• Ostwald ripening: small droplets dissolve and their molecules diffuse through the water to larger droplets, which grow. It is driven by the slight water solubility of some flavor components. It is a particular problem with more water-soluble oils and with very fine emulsions.
• Phase inversion: an O/W emulsion turns into W/O, usually because of too much oil or a poor emulsifier choice. It is rare in finished flavor emulsions but can occur during processing.

In practice these mechanisms interact. A batch with a few oversized droplets will cream faster; creamed droplets are packed closely and coalesce more easily; coalesced droplets cream faster still.

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