Using Agglomeration

Agglomeration can provide answers to many of today's product development challenges. The food industry is under constant pressure to control material and processing costs. Using agglomerated ingredients minimizes material loss, reduces process cycle time, and allows the use of less-than-optimal equipment. In addition, production loses fewer batches to cross-contamination and inconsistency, and controlling dust improves plant safety. Products that address health concerns create new opportunities in the area of dispersion that make agglomerated ingredients necessary.

In addition, retail products that allow the consumer to prepare a home-cooked meal quickly continue to gain in popularity. According to Bill Schmitz, president of Main Street Ingredients, La Crosse, WI, "The process of agglomeration may assist food manufacturers in the creation of innovative products that are convenient for consumers to prepare."

Agglomeration is the process of taking smaller particles and processing them so that they form larger particles. Agglomerated ingredients exhibit better flowability and reduced dusting for ease of handling in the plant, as well as improved dispersion into solution for the processor or consumer.

Manufacturers use a number of different processes to agglomerate material, and although specific agglomeration processes are proprietary, manufacturers commonly use a rewet process. In this method, liquid is introduced to the surface of the powder particles. Wetting the surface of the powder particles makes them tacky. "As these particles interact with each other, they tend to build a larger granule," says Bob Kendall, director of CWS starch at National Starch and Chemical Company, Bridgewater, NJ.

At this point, the agglomerate is soft and has not been sized. The agglomerate will go through drying, sifting and possibly size reduction. The objective is to achieve specific attributes beyond the increase in particle size. As an example, Scott Riefler, president of TIC Gums, Belcamp, MD, notes that "when this agglomerated particle hits water, yes, it's bigger and, yes, the outside still wants to get sticky; but now we've got channels to migrate right into the interior of this particle, so it greatly facilitates the hydration rate."

For instance, high-fat ingredients will not become tacky with water and would be difficult to agglomerate using this process. "The surface has to be wettable, or somehow solubilized," states Lorraine Tam, Ph.D., research and development manager at Griffith Laboratories, Alsip, IL. "Otherwise, you are going to have to use a tack system to hold the particles together."

The composition of that liquid system can be the key to success. According to Rudy Rott, vice president of operations for Main Street Ingredients, a number of process aids can be used in agglomeration, "some may be mixed with water and others may be mixed with other liquids. Process aids are proprietary to the manufacturer."

Schmitz continues by stating that the input of that additional ingredient at the agglomeration phase might help enable putting that ingredient quickly into solution.

As with any other food ingredient, the product is evaluated after creation. In the case of agglomerated whey proteins, Marcela Cota Rivas, the technical and nutritional development director for Vitalus Nutrition Inc., Abbotsford, B.C., says: "We monitor particle hardness and other powder properties that influence the mixing quality, like wettability, sinkability, dispersibility and solubility. If the adhesiveness of the particles is not strong enough, the agglomerates will break down or crumble, resulting in the creation of fines and/or smaller agglomerates, which influence the powder properties. This can happen during the process of agglomeration itself or during handling, storage and transportation. If the particle is too hard, it's not going to dissolve as fully. You might get a gritty mouthfeel."

These agglomerated products are used for functional, nutritional and biological benefits. "The regular isolates and concentrates are used in applications where they don't necessarily need to solubilize quickly, like in protein bars," says Cota Rivas. "The agglomerated products are mostly used for powder drink mixes where the customer is looking for something that is going to dissolve quickly." She adds that the terms "instant" and "agglomerated" refer to the same products -- "agglomeration is the process of making a powder 'instant.'"

Schmitz explains, "Whey proteins and caseinates aren't very dispersible by themselves, so the agglomeration allows for that to happen." With agglomerated milk powders and proteins, "our keys are the dispersibility, flowability, dedusting and the controlled particle size," he continues.

Not only does agglomeration aid dispersion, it increases flowability. This is an important characteristic for fine powders that would tend to bridge in filling equipment. "You increase the particle size and it creates potential for that product to flow that would not flow before," adds Rott.

In addition to improved flowability and reduced dusting, Cota Rivas details another benefit of agglomerated whey proteins for manufacturing: "When (processors) use an open mixing tank with high shear, it causes a lot of foaming. This is a processing problem for some manufacturers, and they prefer agglomerated product because it is easier to dissolve and mixing times are shorter."

The number of applications for these agglomerated products is growing as a result of several trends. First, the need for convenience allows for the development of new products. As an example, Schmitz describes an application in which the developer can "create something that kids can stir up as opposed to the parent doing it. It's something that consumers will look for."

Cota Rivas notes a second trend that's expanding the use of these products: "I would not limit the application of an agglomerated material to just powdered drink mixes. A lot of people are reformulating, coming up with new high-protein, low-carbohydrate products." For example, manufacturers are redesigning instant soup mixes with more protein and less carbohydrate these days. Agglomeration is necessary to ensure good dispersion of the mix into hot water.

If formulators use an agglomerated ingredient to address a problem with dispersion, Schmitz advises that the whole system be taken into account. "Maybe there's a minor ingredient that will offset agglomerating the other ingredients," he notes. For example, even if a dairy ingredient in is the main component of a dry blend, other ingredients, such as gums, starch and flour, might actually cause or contribute to the problem of the dry blend going into solution poorly.

It also depends on the way the ingredient will be used. In a coffee-dispensing machine, the agglomeration of an ingredient would need to solve more than one problem. "The nonfat dried milk has to be a certain particle size," says Schmitz, "or it will not work properly in the machines. You are making it dispersible, and the flowability is also an issue."

Finally, agglomeration is not always used to improve solubility. In some applications, the tackiness developed by solubilized whey protein is detrimental to processing, but solubilization in the finished product is desired. For example, consider the creation of a form of whey protein for a granular application. "For the granulated product, we are not adding any instantizing aid," says Cota Rivas. "We are actually making this product less soluble. This granular product can also be used for tableting applications."

Agglomerated flour was introduced to the retail consumer in 1963. "We introduced it really to solve one of the biggest complaints consumers had about flour, and that was flour dust," says Pam Brewer, spokesperson for General Mills in Minneapolis. The most widely known benefit of this product today is dispersion. "We found it was particularly useful in making lump-free sauces and gravies because it disperses instantly in cold liquids," she continues, adding that delicate batters benefit from agglomerated flour, as processors can reduce the level of required mixing time to achieve dispersion.

Agglomeration allows for great flexibility in terms of the application of moisture and heat to the flour. "You can get varying degrees between an agglomerated product, which is dry-heated, and a pregelatinized product by manipulating the amount of water or steam that you add," says Tam.

Agglomeration can affect ingredient functionality when it comes to flours. "When you add dry heat to flours or starch, you end up precipitating protein on the surface, which prevents the starch from fully swelling," continues Tam. "With the dry-heated flours, they are great when they are added to cold water, as in a cook-up gravy, but when they are added to hot water, as in an instant gravy, it is difficult to achieve the same viscosity."

Product designers might initially think they've run into problems when switching to agglomerated flour. "Sometimes your batters or doughs will look different because it absorbs the liquids and the fats differently, but the end product comes out the same," Brewer comments.

Agglomeration can also help manufacturers keep lumps out of gum solutions. Hydrocolloids, or gums, are high-molecular-weight polymers, "and when a gum particle hits water, the very first thing that happens is that the outer shell, or the outer surface, absorbs water," says Riefler. "Because it is a high-molecular-weight material, it gets very, very sticky. Once the outer shell sees water, the migration of that water into the interior of the particle is slow, because it is actually water migrating through a solid. When gum particles bump into each other they'll stick," and before you know it, "you have a fish-eye, or a gum ball," he cautions.

Riefler also explains what it means for an ingredient to go into solution. "It's really a function of it fully hydrating -- that it truly dissolves in water. All the little sites that can associate through hydrogen bonding with water do so, and that's when it finally goes into solution."

As an example, Riefler describes a table syrup operation where the initial mixing step with water, sugar, carboxymethylcellulose (CMC) and other ingredients is 10 minutes. He explains that if gum balls form initially, the mixer operator has to choose between mixing the product longer or dumping it with or without filtering out the lumps. Allowing more mixing time will reduce efficiency, while filtering out the lumps will decrease the amount of gum in the formulation. If the lumps of gum remain in the product, they will hydrate over time, but the viscosity measured at the quality-control step will be inaccurate because the gum will not be fully hydrated.

According to Riefler, gum will go into solution more easily with "mixing devices -- where you can feed powder into an in-line stream of liquid with mechanical agitation at the point of addition. Agglomeration is a solution to a manufacturer who is being asked to process gums in equipment that wasn't necessarily designed for it." He adds that manufacturers often use oil to disperse the gum before it is added to water, but the oil will slow the hydration of the gum and will add cost to formulations where it is only used as a processing aid.

The tendency to lump varies from gum to gum, and the gums' agglomerated counterparts reflect that range. "When you agglomerate gums, you get the same spectrum of performance. An agglomerated gum arabic will go into solution with little to no agitation. At the other end of that spectrum, an agglomerated xanthan or CMC, while the hydration characteristics are greatly improved, still require good agitation," says Riefler.

An agglomerated gum will not necessarily provide faster hydration than the powder. "The hydration depends a lot of the time on dispersion and agitation," says Gene Brotsky, senior technical service representative at Rhodia Inc., Cranbury, NJ. "The agglomerated guar will go into solution faster than unagglomerated if the dispersion or agitation is insufficient, because the unagglomerated may clump up and then take a long time. If you have high-speed dispersion and agitation, then the guar powders go in faster."

There is also a safety consideration when looking at agglomerated gum. Agglomerated gum significantly reduces dusting, and according to Riefler, that's very important because "if you put gum on the floor and get it a little wet, it gets very slippery. There is an industrial hazard related with gum use ... and the use of an agglomerated gum helps reduce that as well."

Some food applications require "instant starches, either cold-water-swelling or traditional drum-dried pregelatinzed, to offer lump-free dispersibility and instant viscosity, quick hydration rate, while maintaining smooth appearance and texture," according to Jessie Zhao, Ph.D., senior food scientist II at AVEBE America Inc., Princeton, NJ. "The pregelatinized starches in the powdered form have a tendency to form undispersible lumps when introduced into aqueous systems. The process of agglomeration of these starch powders has reduced this problem to a great extent."

Kendall says: "You might have a problem if your product's not agglomerated, because the starch may be wetting out too quickly. You're not getting the right viscosity because you've literally got lumps of starch in your finished product. Agglomeration is used for handling at the consumer and the industrial level."

According to Kendall, applications include consumer convenience meals, where a powder is being reconstituted in some way. "Typical uses have been things like instant soups, where you take a powder and add it to hot water," he says, and also, "sugar-free puddings where you don't have the sugar to act as a diluent in getting the starch into solution. Agglomerated starches are used by many chefs in preparation, where they don't have the time to cook up something separately."

Medical products can also benefit from agglomeration. Some products can effectively thicken beverages and other thin liquids to assist patients with swallowing disorders. "The dysphagia products are of a particular particle-size distribution that allows the product to be added to the liquid without any sort of lumping. If there were lumps it would cause issues for the dysphagia patient," says Shana Brewer, a food scientist at National Starch.

In selecting an agglomerated starch, Zhao advises, "Lump-free dispersibility is always the No. 1 requirement. Quick hydration rate or reaching maximum viscosity within short time is a second important consideration, and this is one of the major challenges to starch manufacturers. In addition, one must consider the end food product appearance and texture. Some agglomerated starches impart coarse or grainy texture while others are smooth. Finally, bulk density and particle-size distribution are key to powder mix uniformity."

Maltodextrin is widely used over many product lines. Although lumping is not typically an issue with this ingredient, its functionality can be enhanced through agglomeration. "Some applications include: dry mix beverages, infant formula, sports and nutrition products, artificial sweeteners, gum and hydrocolloid blends, spices and seasoning blends, soup and sauce mixes, and nutraceutical tablets and supplement products," says Tonya Armstrong, senior applications scientist at Grain Processing Corporation (GPC), Muscatine, IA. Maltodextrin may be used as a carrier, dispersing aid or bulking agent, and agglomeration improves all of those properties.

"Currently, the customers in the food industry are looking for convenience," explains Armstrong. "Agglomerated maltodextrins, when used in dry-mix products, speed the dispersion and hydration of the dry mix -- i.e., soup or beverage -- so that the consumer can more quickly use the dry mix. Some things to consider when choosing an agglomerated product are the following: particle-size selection, flow properties and dispersibility, and bulking capacity needed for the dry mix. For most customers, they have chosen an agglomerated product because they need better flow, dispersibility and a specific particle size for dry blending with the other ingredients. The customer's product may also need to take up space or volume in a package and (they) would choose the appropriate agglomerated maltodextrin for this application."

Armstrong gives the following advice about processing: "An agglomerated maltodextrin is more fragile than a finer-particle-sized ingredient. This means that a manufacturer may have to add the agglomerated maltodextrin at the end of the mixing process if their mixing process is severe, i.e., long mixing in a ribbon blender."

In addition to viscosifiers, agglomeration is also used with ingredients that contribute flavor and color. Wet processors who use chicken broth can face several challenges. "Powdered products will clump up and require a higher-shear mixer that can be detrimental to the formulation," says Bob Hoopingarner, vice president of sales and marketing at International Dehydrated Foods, Inc. (IDF), Springfield, MO. "The fact that our 32% frozen broths are still 68% water has caused most forward-looking wet processors to convert or at least start analyzing the advantages of IDF agglomerated products." Because chicken broth needs to go into solution in applications such as soups, sauces and gravies, solubility is a critical attribute. "The ease of use is key to meeting the demand of the consumer, whether it is a processing plant or a consumer reconstituting a dry mix," adds Hoopingarner.

Hoopingarner describes the structure of the agglomerated product as "honey-combed." The porous shape allows the water to penetrate into the particle so that it dissolves without forming lumps. "In dry mixes going to industrial users or retail and foodservice applications like marinades, soups, sauces, gravies, etc., the agglomerated broth ... goes into suspension, even in cold water, to shorten the preparation time and get the product to the table faster," he says.

Powdered colors can also present problems for manufacturing facilities. "Powdered colors generate dust in the air, which is not always easy to see," says Karen Brimmer, group supervisor at Sensient Technologies, St. Louis. "It will eventually show up on walls, floors and in adjoining offices when it contacts water. Dust affects operator morale in terms of personal cleanliness, may cause cross-contamination and requires extra time to clean production areas."

Several granular forms of color address the issue of dusting. "Granular forms of food dyes can be produced by a variety of methods, including agglomeration, extrusion, etc.," says Brimmer. "All of these products offer substantial reduction in dust control and, when used, will reduce dust and cross-contamination issues. Agglomerated dyes are porous, and therefore these products have the added benefit that they dissolve faster than any of the other forms of granular color."

As individual ingredients benefit from agglomeration, so do blends. "An agglomerated blend ensures a homogeneous mixture and minimizes stratification through the distribution chain. The disadvantage is cost," elaborates Zhao.

"If you were doing blends that had vitamin enrichment or mineral enrichment, it would be one way to achieve a uniform dispersion of very minute quantities of material," adds Tam. "You could introduce the minute ingredient into the water or tack system, which will be used to wet the particles' surface."

The agglomeration of blends has benefits for processing, as well as acts like a hedge against reverse engineering. "If the agglomerated maltodextrin cannot be easily mixed with the customer's ingredient, it may be to their benefit to coagglomerate," says Armstrong, and "it may make their blend more 'proprietary' or secret if all of the ingredients are coagglomerated."

The benefit of the agglomerated particle is that it is held together loosely enough that it will solubilize quickly in water. A drawback to this structure is that it requires special handling to remain intact. Tam notes that abrasiveness from some ingredients, such as salt or pneumatic conveying, could break down the agglomerate.

In addition to process considerations, Zhao states that agglomerated products will also take up more warehouse space per unit of weight. However, manufacturers can reduce material costs in terms of handling and formulation when working with agglomerates.

By creating less dust, the ingredient is sold to the customer instead of fouling the plant. "The reduction or elimination of dust means less time spent cleaning production areas, easier weighing, and minimal chance for cross-contamination," notes Brimmer. "In turn, less dust can lead to reduced production costs."

Improved dispersion also reduces material and processing costs. For example, manufacturers can reduce the levels of starch or gum used by eliminating lumps in solution. With agglomeration, functionality isn't lost. Mixing time is also reduced when products dissolve more easily. "Everybody is looking to decrease their cycle times," concludes Riefler.

When it all eventually boils down, everyone appreciates a healthier bottom line. In many cases, agglomeration may just be the key process that helps properly developed products stick around for the long haul.

Karen Grenus, Ph.D., has eight years combined experience in applied research and product development in the area of dry blends for savory applications. She holds a doctorate degree in Agricultural and Biological Engineering from Purdue University, West Lafayette, IN.

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