Shear and Flow in a Salad Dressings Process – Don’t Neglect One or the Other

Written by Colm Swan, former Dressings, Sauces & Condiments Market Manager

Not all shear mixers are created equal. Some provide a huge amount of shear, perfect for homogenizing oil in water but sacrifice flow. As a result, these mixers must be on mechanical lift stands to lift the mixer up and down throughout the batch. This requires a lot of additional ceiling height and maintenance for the lift itself.

Other “squirrel cage” mixers are designed to provide massive amounts of flow in the tank which allows manufactures to combine immiscible liquids like oil and water. However, due to the lower shear rate, these mixers are only capable of making a coarse emulsion. Typically, they do not reduce oil droplet size enough to create a stable emulsion. They also struggle to disperse dry ingredients that are prone to clumping such as starches and hydrocolloids. As a result, this coarse emulsion requires a secondary “Finishing” step with an inline shear pump or mill. This limits a manufactures throughput and can create product inconsistencies.

When building an emulsion, it is crucial to have high shear to disperse the oil into the water phase as it is being added. If there is insufficient shear, then adding oil will take a long time. Adding the oil too fast in a subpar shear environment will result in poor emulsion stability over shelf life or a broken emulsion during processing. Disaster! Once this emulsion is broken, the two phases will not go back together no matter how much shear you throw at it.

Additionally, as oil is being added and emulsified into the water phase, viscosity of the product begins to increase. Therefore, it is vital that the mixer you are using is also delivering high flow in the tank. The Admix Rotosolver® provides both these attributes. The unique design of the Rotosolver delivers high shear and high flow, eliminating the need for mechanical mixer lifts and/or secondary milling of pourable dressings.

Before using Rotosolvers, one Admix customer was using a competitor’s high shear mixer on a mechanical lift. The manufacturer had one mixer for two tanks. The lift allowed them to move the mixer from one tank to the other. This seemed like a useful feature at first, but they soon found that this severely limited their throughput. One tank sat idle while the mixer was making product in the other. Furthermore, the customer struggled to produce a homogeneous product even with the ability to lift the mixer up and down throughout the batch. When they switched to Rotosolvers, they eliminated their need for mechanical lifts and were able to dramatically increase their capacity by having a mixer on each tank that produced enough flow and shear to give repeatable results every batch.

If you think your process is lacking shear or flow, contact Christian Thayer, at or call 802-779-4120.