Mixing and Blending Equipment Offers Efficiency, Consistency

 By Parth Ashish Bhave; *Anas Ejaz Shaikh

Blending involves combining solid or liquid substances into a medium by dissolution, emulsification or dispersion so as to produce a smooth and homogenous product. Dairy industry is no stranger to this pivotal chemical engineering operation and has exploited its power to produce an array of products with superior quality.

An example to the use of blending operation in dairy industry would be blending comminuted butter using batch blender with heavy-duty contrarotrating ‘Z’ shaped blades in order to finely disperse solid fat to achieve desired plasticity. Scraped surface technology is used to produce emulsions in manufacturing low fat spreads and can be used in a batch system or continuous system. Butters from two different buttermakers can be blended together with a static in-line mixers and continuous butter manufacturing operations often rely on high shear mixing equipment to produce homogeneous product with consistent quality.

Although butter manufactures have extensively used blending operations to their benefits, dairy industry is running into problems with incorporating mixing powders into liquids. Many such problems with blending are encountered not only in butter making but several other dairy processes which involve blending as an integral part. Effective blending solutions can, thus, be sought after in order to increase the line efficiency in dairy plants.

Some of the challenges encountered in blending processes are listed below and their solutions are discussed:

Air Incorporation and Foaming

Air incorporated while mixing ingredients or by whipping action of mixers tends to get trapped into the product. With foam stabilizing ingredients such as proteins, the air bubbles which have risen to the top then form stable foam on the surface of the product. Dissolution of air back into the product can then take place causing serious operational difficulties. This includes cavitation in homogenizers often resulting in higher costs in terms of maintenance and increased heat exchanger fouling leading to short run times and increased clean time. Foam formation in vessels can be difficult to clear and can lead to substantial product losses due to increase in volumes. Product quality is also hampered due to oxidative browning and formation of off-flavors. It can also lead to reduction in content of air sensitive nutrients like vitamin C in final product.

Although an optimal solution to such an intricate problem would involve consideration of parameters like processing temperature, product formulations, and type of ingredients used; right type of blending equipment can help resolve this issue. Vacuum mixers can be an effective tool to minimize air incorporation and foam formation. Working mechanism of this mixer involves removal of air from the mixing tank to ensure that there is no air at the liquid interface and that liquid surface now borders vacuum. This prevents formation of foam while carrying out the mixing operation. Solids are then injected through powder inlets which are positioned on the mixing tank at levels well below the liquid surface and the vacuum inside the tank is maintained by usage of valves that flip open and close intermittently. This further minimizes the foaming risks.

However, some air that gets trapped into the solid particulates inevitably enters the product and can be impossible to hence remove. Value opening time should thus be optimized into order to lower the chances of air trapping into the solid particulates.

Another approach to achieve minimized air incorporation involves reduction in mixing time. Lower mixing time can be achieved through use of effective mixers like rotor and stator. Rotor and stator fall into the category of high shear mixing equipment which can be operated under batch or in-line continuous conditions and creates a homogenized product due to effective wetting of solid particles. In these mixers, liquids and solids are pushed downward during the mixing operation where blades underneath the rotor push the mixture contents through a perforated stator to achieve high shear rates necessary to dissolve or emulsify solids efficiently like skim milk powder. However, proper control over the mixing vortex is absolutely crucial in order to prevent surface turbulence and avoid vortex from reaching the mixing head, both of which can lead to air incorporation into the product.

With this discussion, it would be conclusive to deduce that the optimal solution to this problem involves usage of high shear mixing equipment like rotor and stator combined with vacuum, in order to improve process and line efficiency.

  1. Lumping and Clogging

Viscous stabilizers and certain other powders tend to form lumps in the liquid medium. This occurs when relatively large amount of powder is added at once forming a gel on the surface of solid. This impenetrable gel layer can cause incomplete wetting of solids particulates. Lumps can be detrimental to the final quality of the product by inducing sedimentation thereby lowering its shelf life. It can also create problems with sterilization step as insides of the lump may not reach the required temperature. Large lumps can clog equipments, hampering operational efficiency and production capacity.

*B.Tech., Department of Dyestuff and Intermediates Technology, Institute of Chemical Technology, Mumbai.
*B.Tech., Department of Food Engineering and Technology, Institute of Chemical Technology, Mumbai