Dispersing Starches with High Shear Mixers

Starch is used as a thickening, stabilising and binding agent in many food products including soups, sauces, gravies and baked products. Starch can be modified by a number of methods to obtain functional properties such as texture, appearance, viscosity and stability under heating or freezing.

There are many different grades and types of starch available. Unmodified starches are relatively easy to disperse and generally do not increase in viscosity until heated or cooked. However, pregelatinised starches can be more challenging. Pregelatinised starches are sometimes called CWS (cold water swelling) starches. These products can be difficult to disperse and hydrate as they begin to increase in viscosity as soon as they are added to water. 

Because of the way in which pregelatinised starches react when added to water, agglomerates can easily form. These agglomerates become more challenging to disperse as the viscosity of the mix increases and agitation and incorporation becomes increasingly more difficult. This can result in long mixing times to complete dispersion and hydration of the starch when using conventional agitators and mixing methods. These type of mixers do not produce the high shear necessary to break down the agglomerates in the mix. Even after a long mixing time, full yield of the starch is difficult to obtain and a filtration stage may be required to remove any lumps remaining in the mix.

The simplest way to overcome these problems is to use a high shear mixer in place of the conventional mixing equipment. A high shear mixer can rapidly incorporate pregelatinised starch powder and hydrate it without forming agglomerates, all in a fraction of the time taken by conventional agitators. 

This is done as follows: The vessel is charged with liquid and the mixer is started. The starch is added to the water as rapidly as the mixer will take it in. The high speed rotation of the rotor blades creates a powerful suction which draws the liquid and powder into the workhead where they are rapidly mixed.

Centrifugal force drives the powders and liquid towards the periphery of the workhead, where they are subjected to intense high shear in the gap between the rotor and stator wall. The product is forced out of the stator and projected radially back into the body of the mix.

Fresh materials are simultaneously drawn into the workhead. In a short mixing cycle all the material passes many times through the workhead, progressively reducing the particle size and exposing an increasing surface area to the surrounding liquid, accelerating hydration. This results in an agglomerate-free mix so filtration stages and long mixing times can be eliminated.

The type of high shear mixer suitable for each manufacturing process will differ depending on batch size, viscosity of the end product and other ingredient in the mix. But generally for small volumes Silverson Machines would recommend a high shear Batch mixer for rapid powder incorporating and an agglomerate-free dispersion. 

For large-scale production, the Silverson Flashmix offers a fast, clean and efficient means of dispersing starch. Powders can be added into the hopper at floor level so there is no need for additional conveying equipment. The Flashmix can rapidly incorporate large volumes of powder with minimised aeration, minimised cleaning requirements and minimum operator input required. Unlike many other powder/liquid mixers, which use vacuum to pull in powders, the Flashmix literally forces powder into the liquid stream. This not only allows it to disperse and hydrate large volumes of powders, it means it can be used with higher viscosity mixes such as starches.

Dispersing starches with a Silverson High Shear mixer can:

• Fully incorporate starches despite the increase in viscosity.
• Produce an agglomerate-free mix.
• Maximise yield of thickening effect as the starch is fully hydrated.
• In some cases products can be re-formulated with reduced starch content as full yield can be achieved, cutting raw material costs.
• Achieve consistent product quality and greater uniformity between batches.
• Reduce mixing times by eliminating the need for controlled powder addition and premixing of powders.
• Eliminate the need for a filtration stage.
• Virtually eliminate operator error during powder addition as starches can be added to the mix as quickly as the mixer can take it in.

If you would like to find out more about how Silverson Machines can be beneficial when dispersing starches and other gums and thickening agents, please visit the Silverson website: www.silverson.co.uk or email sales@silverson.co.uk