Meeting Modern Demands for Solids/Liquid Mixing

Market expectations continually develop and change, and the food and beverage market is no exception. The demand for new and varied products is rising with consumers being more aware of the health benefits and qualities of foods. In the dairy industry, for example, there is an increasing use of milk derivatives, and vitamin and mineral fortification is an important feature of products offered. Producers need to deliver more in a competitive market place where cost, quality, and variety are all important factors. Technology has to provide a way for manufacturers to meet the need for increased efficiencies, process flexibility, and reliability but with consistent, high-quality results.
    Mixing is an important part of food processing on all scales. Whether at home in the kitchen making a party cake or in a large factory producing tons of ice cream, the quality of the mixing has a huge impact on the quality of the end product. Mixing may require the combination of multiple liquids or pastes or can be the method for introducing dry powders to liquids. It is a vital process in the production of foods including dairy products, soups and sauces, baby foods, fruit preparation, syrups, and jams, to name but a few.

Solid/Liquid Mixing
Where the mixing of solids and liquids is required the need for good dispersion is a common factor in all batch or continuous production applications. The consistency produced will impact the final taste, texture, and color of the food or beverage and the final product quality depends on continually achieving the correct consistency with homogenized and stable emulsions.
    The shear a mixer generates also has an important role to play in the characteristics of the food produced. Shear is necessary to puree solid ingredients, homogenize, and produce cohesive emulsions. A high shear forces even difficult soluble ingredients into a solution or dispersion and avoids undesirable qualities such as foaming, clogging, lumps, or “fish eyes.”
    Traditionally atmospheric mixing has been widely used in the food and beverage markets, but this technique presents some challenges to the process, and modern demands are increasingly requiring more sophisticated recombination technology. Atmospheric mixers typically have an open, gravity-fed powder transport system, which has hygienic risks and creates a way for vapors to enter into the dry parts of the machinery. Such effects reduce the running time for the mixer and increase cleaning and maintenance requirements.
    A top, gravity-fed system also allows air into the mixture and makes the mixing process less efficient. In areas such as dairy production, the introduction of air leads to the need for a longer resting period before pasteurization can take place, extending the overall process time. Air can also affect color, flavor, oxidation, nutritional stability, and, ultimately, the shelf life of the product. A mixing system with a vacuum powder transport has a number of advantages with increased solids capacity and insensitivity to free vortex formation improving mixing efficiency. Unlike traditional gravity-fed systems, the vacuum provides a bottom-fed powder input in a closed environment. This arrangement improves hygienic factors and the vacuum efficiently removes air from the mixture, leading to longer running times and, in turn, increased capacity and reduced maintenance costs.  
    As the powder is sucked in beneath the circulating liquid in the mixer tank, increased solid content can be used even with higher viscosities. The high shear created by a vacuum mixer gives good dispersion and tighter emulsions with narrow particle size distribution – a desirable characteristic for production of premium food and beverage products. Integrated de-aeration adds to product quality and improves the reliability of the process. The low-level powder feed mechanism also requires less height for installation than a gravity fed system and provides easier access for maintenance and inspection.
    Keeping the wet side and dry side of a mixing process separate is important as powder entering the wet production area creates hygiene risks. A closed vacuum mixer prevents contamination by keeping the powder contained but back flush of liquid into the powder within the machine will also create production issues. Wet powder will stick to inlet valve seals, reduce their effectiveness, and lead to blockages.
    A high-performance vacuum mixer provides better economy with higher capacity for liquid/powder mixing. Excellent de-aeration efficiency and the high shear with a controlled vortex ensure fine emulsions, improved product quality, and shorter mixing times. The closed system assists with the necessarily high sanitary requirements for the food and beverage industry.
    Mixing is a vital part of food processing and, as such, reliability and running time of this process has a big impact on the capacity of an overall production line. The quality of the mixing has a major influence on the quality and characteristics of the final product.
    Bill Snow is technology group manager, SPX Flow Technology. For more information, visit www.spxft.com