Mayonnaise and salad dressing are oil in water emulsions, and everything that determines their shelf life is decided by droplet size. Smaller and more uniform oil droplets mean a firmer, whiter product, less oil separation on standing and less stabiliser needed in the recipe. The equipment that produces that droplet size is the emulsifying head, and running the process inline rather than in a batch tank is often the difference between a repeatable product and one that varies from batch to batch.
How the shear is generated
An emulsifying pump draws the pre-mix through a rotor and stator assembly where the product is subjected to intense shear in the gap between them. Oil is broken into droplets at the moment it is forced through the gap, and the protein or gum system in the water phase adsorbs onto the new droplet surfaces and holds them apart. Because the head is open, the same unit can also be used to disperse powder and to pump the finished product to a filler, which is why these pumps are normally installed in the line after the oil and water phases have been pre-mixed.
Why inline beats batch on this duty
In a batch tank the shear is applied for a long time and heat builds up from the mechanical work, which damages egg protein and drives off aroma. An inline unit applies shear once, briefly, at a controlled flow rate, so the temperature rise is small and the emulsion can be cooled immediately at the discharge. The result is a narrower droplet distribution, less air entrainment and a shorter residence time at high temperature, all of which improve shelf life.
Process parameters that matter
Flow rate through the head, the rotor and stator geometry, the gap setting, the product temperature and the order in which the phases are introduced. Over-shearing is a real failure mode: too tight a gap or too many passes reheats the product and can break an already formed emulsion, which shows up as a thin, oily dressing. Whether the recipe includes pieces such as herbs, mustard seed or diced vegetables also decides whether the head can be used, because a high shear gap will damage particulates.
What to send us
The recipe and oil to water ratio, the target flow rate, the product viscosity before and after emulsification, the solids content and particle size, the process temperature, the cleaning method and the electrical supply. We will confirm the head diameter, gap, motor power and the CIP arrangement.
