Dispersing Powdered Ingredients—Uniform Blending Is Key

When adding powdered ingredients into food processing lines, the use of the right mixing equipment can not only prevent lumping, but also increase productivity, enhance product quality and reduce energy costs. Powders are common ingredients of the modern food industry. Difficult-to-disperse powders pose challenges for food manufacturers due to formation or lumps or ‘fish-eyes’.

Alfa Laval has developed a versatile new system for high-speed dispersion of powdered ingredients, even the most challenging ones, which maximise uptime while reducing initial investment, operating and maintenance costs.

Powdered ingredients are widely used in the manufacture of food products. In particular, the use of powder additives and functional ingredients, such as texturising additives, nutrients, flavours and colorants, has increased tremendously over the past decades. While these ingredients bring flexibility and consistency to food products, they also present challenges with regard to incorporating powder dispersion units into processing lines.

Most powder mixing technologies require several motors for the supply pump, booster pump, agitator, discharge pump and tank cleaning device. This generally results in higher investment and energy costs.

To address these issues, Alfa Laval has developed an innovative dispersion system that combines two individual types of equipment. This compact, highly reliable system features a single motor that handles all of the tasks of conventional powder mixing systems, yet delivers up to 50 percent in energy savings, superior mixing efficiency, reliable and repeatable mixing quality, and product homogeneity.

Lumps, or ‘fish eyes’, formed during dispersion of a pectin slurry

There are various types of powdered ingredients added to food processing lines. Easy-to-disperse powdered ingredients, such as granulated sugar or skimmed milk powder, generally do not pose lumping problems because moderate shear is sufficient to ensure rapid dispersion and dissolution of the individual powder particles.

However, moderate shear proves challenging when dispersing texturising additives and water-binding powdered ingredients, such as hydrocolloids or concentrated protein powders.

Texturising additives in powder form are used in many food formulations to optimise texture and mouthfeel. These include, for example, xanthan in vinaigrette, pectin in yoghurts and fruit preparations, sodium carboxymethyl cellulose (CMC) in beverages, and alginates in desserts and ice cream.

Due to the exceptionally high water-binding properties of these hydrocolloids, the dosing level is very low, typically between 0.1 and 0.5 percent of the formulation and sometimes even less. However, these high water-binding properties also pose problems during dispersion. When the powder comes into contact with water or other liquids, its outer surface immediately forms a gel layer, which then prevents water from penetrating and hydrating the core of the powder mass. If the dispersion method proves inadequate, it causes the formation of small gelatinous lumps, called ‘fish eyes’, which are very difficult to disintegrate.

These lumps usually are retained in filters along the processing line, but may also end up in the final product. This lost fraction of texturising additives impacts the quality of the food product, reducing the desired effect in the final product.

Protein ingredients in powder form generally contain between 70 percent and 90 percent protein, and are added for their nutritional and texturising properties. Typical protein ingredients include caseinates, whey protein concentrates or vegetable protein isolates.

During dispersion, these protein ingredients present issues that are similar to those of hydrocolloids; the core of the powder mass hydrates very slowly. Some manufacturers, in fact, put the mixture into cold storage overnight under moderate agitation in order to ensure complete hydration before further processing.

Powder dissolving station using the combination an Alfa Laval Hybrid Powder Mixer and Alfa Laval Rotary Jet Mixer.

One of these two methods is typically used to disperse powdered ingredients into a liquid phase, such as water or milk:

• 1. Dispersion onto the surface of a liquid in a tank, by pouring the powdered ingredient directly over the surface of the liquid in a dispersion tank during agitation.

• 2. Dispersion using a powder mixer, either in-line while transferring the liquid between two tanks or, more commonly, during recirculation in a dispersion tank until the entire amount of powder has been dissolved.

Using an inadequate powder dispersion method and inadequate mixing equipment results not only in productivity losses, but also in inferior product quality. To prevent lumping and achieve complete hydration of the powdered ingredients, extra buffer tanks may be required.

Alfa Laval Hybrid Powder Mixer

The Alfa Laval Hybrid Powder Mixer used in combination with the Alfa Laval Rotary Jet Mixer offers an innovative way to deal with powder dispersion issues. Food manufacturers can now take advantage of optimal mixing efficiency and low cost of ownership.

By combining the two units into a single, highly efficient system, Alfa Laval enables instant and uniform dispersion of even the most challenging powdered ingredients using a single motor. After completion of the mixing cycle, the same system may also be used to drain and clean the tank.

The Alfa Laval Hybrid Powder Mixer features a uniquely designed two-stage pump, one rotor stator stage and one pump stage fitted with a motor with a frequency converter. The pump enables an output pressure of up to four bars without requiring an additional pump. It also drives the circulation loop to the mixing tank.

Due to its high output pressure, the Alfa Laval Hybrid Powder Mixer may also be used as a discharge pump to empty the mixing tank after powder dispersion has been completed.

How it works:

Unlike conventional powder mixers, it creates high dynamic shear in three steps using a single motor shaft. This requires less energy to ensure complete dissolution of the powder.

• Step 1: The injector pre-blends the powder and liquid
• Step 2: The rotor/shaft provides the main shear
• Step 3: The impeller provides additional shear and pumps out the mixture under high pressure

These three steps provide high flow velocity, thereby reducing the risk of blockage. This is particularly relevant when processing shear-thinning texturising additives because energy consumption can be kept low even when blending high viscosity food products.

Alfa Laval Rotary Jet Mixer>

Installed inside the mixing tank on the circulation loop, this rotating four-nozzle device is powered by the product flow and pressure from the Hybrid Powder Mixer.

• Efficient powder dispersion: The Rotary Jet Mixer actually provides a fourth step for additional shear. When it flows through the nozzles, the product experiences substantial shear, which promotes the disintegration of any remaining lumps. This speeds the dispersion of the most challenging powdered ingredients and ensures product homogeneity without having to add an agitator.
• Self-cleaning system: In addition to providing efficient powder-dispersion, the Alfa Laval Rotary Jet Mixer can also be used as highly effective tank cleaning machine for the mixing tank.
• Time- and energy-efficient dissolution: Powdered ingredients are therefore already dissolved when entering the tank, making recirculation unnecessary. This saves time, reduces energy consumption and boosts production capacity.

Alfa Laval Hybrid Powder Mixer has been successfully tested and installed for use in various food and beverage applications—both as a stand-alone mixer and as part of a complete powder dissolution station in combination with the Alfa Laval Rotary Jet Mixer. Combining the Alfa Laval Hybrid Powder Mixer with the Alfa Laval Rotary Jet Mixer provides high-speed mixing efficiency and ensures gentle handling.

The efficient mixing pattern ensures dispersion of the powder in individual particles and immediate hydration in the fluid mass. The combination has proven especially efficient in achieving product homogeneity when dispersing texturising additives such as CMC, pectin, xanthan or carrageenan. As versatile as it is reliable, the mixing system easily handles high-viscosity fluids, such as a three-percent solution of high-viscosity CMC, but can also handles rapid dispersion of sugar and milk powder at several tons per hour.