Cereals & Grains Association
Log In

03 Issues & Trends
Cereal Foods World, Vol. 64, No. 4
DOI: https://doi.org/10.1094/CFW-64-4-0042
Print To PDF
High-Pressure Hydration System for Dough Mixing Applications
Bernhard Noll
Rapidojet GmbH, Michelbach / Bilz, Germany

© 2019 AACC International, Inc.

Abstract

Starter materials for food processing are often produced by combining water or other liquids with basic dry ingredients. Effective hydration of dry materials is promoted by a large, highly accessible surface area at the time of moistening and large differences in speeds between dry and wet materials during moistening. The Rapidojet high-pressure hydration and mixing system offers a revolutionary solution. Dry material is conveyed continuously into a vertical mixing tube by a dosing unit and sprayed with liquid at high pressure. Large surface areas are achieved for the dry materials through isolation during freefall and for liquids by enlargement of the liquid surface area through breaking of the liquid into small droplets. The moistened material leaves the mixing chamber in the form of minute particles, and the fully hydrated particles become a uniform mass when they land in the hopper of a pump or other vessel. The high-pressure hydration and mixing system and its potential baking, food, and flour milling applications are described.




One of the most important food ingredients is a simple molecule—water. In addition to its significance as an essential nutrient, it also plays a key role in processing and producing foods. Starter materials for food processing are often produced by combining water or other liquids with basic dry ingredients. If the basic dry ingredient is flour, then the mixing ratio of wet to dry ingredients determines whether a crumbly dry mass (e.g., pasta products), solid viscoelastic dough (e.g., bakery products), or liquid mixture (e.g., waffle dough, batter) is produced. If the basic dry ingredient is potato flakes or masa, the mixture of wet and dry ingredients can be used to create a potato mash, crisps, corn chips, or other snack food products. Hydrocolloids are used to produce gels, and vegetable proteins are used as meat substitutes in vegetarian products. Until recently, the methods available for efficiently binding liquid molecules with dry ingredients in food products have been limited. Due to a number of factors, many substances are extremely resistant to hydration:

  • Many dry materials are hydrophobic, and water simply runs off.
  • Other dry materials are extremely hydrophilic, and when they make contact with the liquid first, they “steal” the water from the rest of the materials present.
  • The surface tension of the water prevents the water from spreading well over a surface.
  • When powder is introduced into water, the water penetrates into the outer layer and forms a gel that prevents further penetration (i.e., gel blocking). As a consequence, lumps are formed.
  • Foods generally are structure-sensitive matrices with properties that can be irreversibly destroyed by high shear forces during mixing.

Effective hydration of dry materials is promoted by two conditions:

  1. A large, highly accessible surface area at the time of moistening.
  2. Large differences in speeds between dry and wet materials during moistening.

These conditions can only be created to a very limited extent using the existing range of stirring and mixing tools. The available mixing technologies are restricted to a maximum hydration range of ~30%. A revolutionary and disruptive solution has been developed and is now available on the market—the Rapidojet high-pressure hydration and mixing system (Fig. 1). The high-pressure, high-speed addition of liquids to dry ingredients, as well as a patented mixing chamber, enables a wider range of hydration levels. The system can be used in food applications to produce hydration levels ranging from 2% (for hydrocolloid solutions) to 65% (for stiff, hydrated biga flour-and-water bread prefermentations). The design of the Rapidojet system is simple: dry material is conveyed continuously into a vertical mixing tube (volumetrically or gravimetrically) by a dosing unit and sprayed with liquid at high pressure.

Within the vertical mixing tube, the dry material is isolated in freefall after contact with a deflector cone. The liquid is injected at high speed (250–500 km/hr) through a high-pressure nozzle and broken into tiny droplets that meet the free-falling dry material in midair. Thus, both factors—a large accessible surface area and large differences in speeds between wet and dry materials—are achieved. Large surface areas are achieved for the dry materials through isolation during freefall and for liquids by enlargement of the liquid surface area through breaking of the liquid into small droplets. The large difference in material speeds ensures a forceful impact—an effect that does not occur with the same intensity in traditional mixing methods. As a result of its high-speed impact, the liquid penetrates much more deeply into dry materials that are difficult to access using traditional mixing techniques.

Despite the intensity of the high-pressure jet, the method is very gentle because no shear forces are generated. The moistened material leaves the mixing chamber in the form of minute particles that are visually perceptible as a “product mist” (Fig. 2). The fully hydrated particles only become a uniform mass when they land in the hopper of a pump or other vessel, such as a mixing bowl, trough, etc.

Furthermore, there is practically no increase in product temperature, which is an undesirable side effect, particularly in intensive mixers. In the high-pressure jet system, it is possible to moisten and heat the product at the same time utilizing hot water. Using this method, starch can be completely gelatinized in one step, or flour can be processed to a “flour custard” or paste. In addition, because staling occurs as a result of starch retrogradation, not evaporation, the high-pressure hydration process can help extend product shelf life.

An essential feature of high-pressure hydration is that the water-binding capacity of dry materials increases significantly due to the more homogeneous bond between the dry and liquid ingredients. For example, in wheat dough the quantity of water needed to produce the same consistency and level of machineability is increased by 5–10%. This effect is also observed with starch. The first high-pressure hydration applications were traditional prefermentations (liquids and solids), but formulations can be adapted to produce completely developed doughs. Although only ~10% of the mixing energy is used, the wheat gluten is activated within fractions of a second in such a way that it “grows together” to form a developed dough, which is a time-dependent operation promoted by enzymatic activities in the dough.

Bakers often use the Rapidojet as a “bowl-filling machine.” The flour is delivered to the existing mixing bowl instantly and is fully and optimally hydrated, with most of the gluten developed (Fig. 3). The prefermentation is then mixed briefly with the remaining ingredients. This essentially doubles the mixing capacity of the system. In addition, use of ice and glycol can be substantially reduced or eliminated.

In addition to the production of liquid (sponge) and solid (biga) prefermentations, many other applications are in use in the baking, food, and flour milling industries. A few examples include

  • Production of potato mash from potato flakes for frozen meals.
  • Production of gluten-free doughs and batters in which the high-pressure jet is used as a continuous mixer.
  • Hydration of pure wheat gluten as a natural baking agent, which reduces required vital wheat gluten by 20%.
  • Instant hydration of wheat bran at well above 200% (Figs. 4 and 5).
  • Production of a clear gel from hydrocolloids such as pectin, pregel starch, xanthan gum, guar gum, etc., without air inclusions (fish eyes or craters), for use in soups, jellies, fruit juices, etc. (Fig. 6).

Preliminary work has been performed for other applications that could be implemented in industrial processes, including

  • Production of germinated cereals (in addition to an intensive cleaning effect, faster penetration by water shortens the germination period) for use in “bread without flour” (also called sprouting).
  • Removing chaff and other contaminants (e.g., mycotoxins such as deoxynivalenol) from a wide range of grains (Fig. 7).
  • Substantial reduction or elimination of tempering (soaking) time for a wide range of grains prior to milling.
  • Malt production with reduced soaking time and water consumption.
  • Moistening of whey powder and casein to produce processed cheese.
  • Moistening of dried blood plasma.
  • Moistening of a wide variety of fiber ingredients (e.g., cellulose, oat spelt, fruit fibers).
  • Production of a variety of sprouted grains and legumes (e.g., mung beans).