Explosion-puffing process

By the mid-1970s research on the potato flake process was over and the commercial applications of the process were assured. This enabled researchers at the Eastern Regional Research Center – Laboratory Chief Eskew and chemical engineers Cording, Nelson Eisenhardt, John Sullivan, Michael Kozempel, Gerald Sapers, Rich Konstance, Mary Jo Egoville and others – to shift their attention to developing other methods for drying fruits and vegetables. Drying fruits and vegetables as a means of preserving them had been used in ancient times. But the two most commonly employed methods – hot-air drying and freeze drying – had limitations. Dehydrating pieces of fruit or vegetable by hot air is slow as is the re-hydration process. The flavor of the re-hydrated pieces often is not good because of the long exposure to high temperatures during drying. Freeze-dried products re-hydrate quickly and their quality is superior to the hot-air dried products, but the drying time is even slower and thus more expensive.1

A third process – developed at the ERRC – incorporates explosion puffing in the dehydration process. Cording had observed that air-dried pieces of fruits and vegetables collapsed on themselves so he hypothesized that if the pieces were puffed up, this would open the inside in a honeycomb effect, making drying easier and quicker.2 The resulting product is similar in quality to the freeze-dried version, but the re-hydration times are even faster. This means that processing costs are much less expensive. In addition, the texture and flavor of the re-hydrated fruits and vegetables compares well with fresh cooked food. The explosion puffing process yields low-moisture – less than four percent – fruit and vegetable pieces. Many fruits and vegetables were processed using explosion puffing; for the most part, the re-hydrated pieces exhibited excellent texture, color, and flavor. In addition, the pieces stored well. The explosion puffing process produced a rapidly reconstituted, high quality, and inexpensive product that tasted fresh.3

Eisenhardt initially was in charge of working on fruits; Sullivan on vegetables.4 Research quickly established that raw fruits and vegetables would disintegrate when explosion puffed. The research also showed a relationship between moisture content of the product and the pressure used. This relationship differed depending on the food that was placed in the puffing gun. In any event, the process aimed at maintaining the porosity of the pieces (since the porosity actually increases in explosion puffing, large pieces could be dried) because porosity made the removal of water easy and rapid.

Initially the fruit or vegetable is hot-air dried to a moisture content between 15% and 35%, a level at which the piece attains a degree of rigidity. The partially-dried pieces are then fed into the "puffing gun." The initial experiments were carried out in a small gun that was heated by an external gas flame. The vegetable or fruit pieces were further heated in the gun while the gun rotated at a speed sufficient to tumble the pieces. Chamber pressure in the gun resulted from steam released from the heating of water in the pieces. In the small gun the time required to obtain the requisite pressure varied from seven to fifteen minutes at which point the product exploded from the gun with a loud bang during. The vegetable or fruit piece expanded – "puffed" – during the explosion.5

The small gun used in the early experiments allowed the researchers to test the feasibility of the explosion puffing process on many varieties of fruits and vegetables. As one of the researchers said "We certainly did not run out of products, we just ran out of time."6 Soon, the process was scaled up with the installation of a large commercial cereal-puffing gun to test commercial-type feed rates on large batches to get reasonable cost estimates. But both the small and large guns had drawbacks: the rough surfaces in the cast iron guns caused food pieces to stick and scorch instead of tumbling feely; they had to be opened and closed manually; and the sealing ring was made of lead.

A second large gun was constructed to eliminate some of these problems: the interior was sand-blasted and nickel-plated and a heat-tolerant rubber gasket was used for sealing instead of lead. This experimental puffing gun was designed specifically for use on large batches of fruits and vegetables and not for puffing cereals. It was constructed to be heated internally by superheated steam and externally by gas burners and the heating cycle was reduced to less than two minutes. The new gun produced vegetable and fruit pieces of superior color and flavor.

Batch-scale production was useful for research purposes, but it was too labor intensive for commercial use. To lower processing costs, a Continuous Explosion Puffing System (CEPS) was developed and built by Cording and Wolfgang Heiland and R.G. Mercado. This device – which reduced costs by running continuously – separated the two major functions: heating and explosion puffing. The heating is done in the main chamber by dispersing superheated steam. The explosion puffing takes place when the discharge piston is released. This reduces the pressure in the discharge chamber from that in the heating chamber to the atmospheric level. The resulting explosion produced a better product with reduced labor costs.7

CEPS was initially developed to produce dried potatoes and carrots, but was later applied to apples, blueberries, pears, celery, beets, sweet potatoes, turnips, rutabagas, onions, peppers, mushrooms, and other commodities.8 In addition to the engineering research, the ERRC conducted extensive quality control studies to test shelf life, flavor, and texture. John Sullivan, Gerald Sapers and others recognized early the need to control enzymatic browning and conducted numerous experiments and studies on flavor control, discovering for example the utility of injecting nitrogen gas with the steam during puffing to prevent deterioration of quality over time.9

The explosion puffing process has been used most successfully in the production of high-quality dehydrated carrot pieces and blueberries. Puffed carrots work well in quick-cooking dehydrated soup mixes where rapid re-hydration occurs and they have been marketed by companies in the United States and in Europe, China, and India. Puffed potatoes are marketed as ingredients in meals for campers and for emergency rations. Explosion-puffed blueberries have been marketed over the years.

1 J.F. Sullivan and J.C. Craig, "The Development of Explosion Puffing," Food Technology 38(2) (1984): 52. This paper proved a very useful source for this section.

2 Interview with Gerald Sapers, conducted by Judah Ginsberg, January 30, 2007.

3 Sullivan and Craig, "The Development of Explosion Puffing," p. 52.

4 Sullivan was given control of both fruits and vegetables when Eisenhardt died. See interview with John Sullivan, conducted by Judah Ginsberg, January 31, 2007.

5 Sullivan and Craig, "The Development of Explosion Puffing." See also, N.H. Eisenhardt, J, Cording, Jr., R.K. Eskew, and J.F. Sullivan, " Quick-Cooking Dehydrated Vegetable Pieces: 1. Properties of Potato and Carrot Products," Food Technology 16(5) (1962): 143-146.

6 Interview with Rich Konstance, conducted by Judah Ginsberg, January 31, 2007.

7 On CEPS, see W.K. Heiland, J.F. Sullivan, R.P. Konstance, J.C. Craig, Jr., J. Cording, Jr., and N.C. Aceto, "A Continuous Explosion Puffing System, Food Technology 31(11) (1977): 32-22 and J.F. Sullivan, R.P. Konstance, N.C. Aceto, W.K. Heiland, and J.C. Craig, Jr., "Continuous Explosion-Puffing of Potatoes," Journal of Food Science 42 (1977): 1462-1463, 1470.

8 Sullivan and Craig, "The Development of Explosion Puffing," p. 55.

9 J.F. Sullivan, "Control of Non-enzymatic Browning in the Dehydration of Fruits and Vegetables" Progress in Food and Nutritional Science 5 (1981): 377-393.


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