US2158354A - Treatment of food materials - Google Patents

Description

May 16, 1939. w. w. COWGILL TREATMENT OF FOOD MATERIALS Filed May 14, 1936 ATTORNEYS Patented May 16, 1930 PATENT oral-e:

mamn'r or soon MATERIALS William W. Cowgill, l'airileld, Conn, assignor to Sardik Incorporated, Jersey poration of Delaware City, N. 1., a cor- Application May 4, 1936,- Serial No. 79,638

5 Claim.

This invention relates to the manufacture -oi food products and more particularly to an improvement in the method of reducing the moisture content of food materials set forth in the 5 patent to Sartakofi' Number 1,908,489, May 9, 1933, although it will be apparent to those skilled in the art that various features of the invention are equally well adapted to other methods of drying material by a contact with a drying surface.

An object of this invention is to provide a method of drying material in which the evaporation of moisture is so controlled and regulated as to insure protection of the material against overheating during the entire drying period, while subjecting it to the most effective drying temperature, thus improving the quality of the. product and increasing the eillciency of the operation. 1 g

This and other objects which will be apparent to those skilled in this particular art are accomplished by means of the invention hereinafter set forth. The accompanying drawing comprises a diagrammatic view showing one arrangement of apparatus which may be employed for carry- 25, ing out the method of the present invention.

In the present invention the drying surface may be of any desired type' but is preferably provided by the outer face of a rotary, interiorly heated drying drum on which the material is carried through the drying zone. The fresh material is continuously delivered to the moving drum surface, dried thereon and then continuously removed therefrom, preferably in the form of a continuousfllm by .a suitable scraper or blade.

Referring to the drawing, a rotary, interiorly heated drying drum 6 is supplied with material to be dried through a feed line it and a feeder head l. The feeder head extends across the to face of the drum and has a plurality of openings 8 through which material is deposited on the drum surface. Immediately adjacent to the feeder head is a heated distributor roll 8 or similar device which operates to disperse the material over the face of the drum as, for exsurface is perfectly clean and free of all particles of pulp and the like after passing the scraper. A flexible blade of steel, the edge of which is pressed against the drum surface with suiilcient pressure to provide the necessary contact across the entire surface has proven to be entirely satisfactory. When the Sartakoff process of drying is followed, such a blade consolidates the particles and removes the dry material from the drum surface in the form of a continuous film, as described in the Sartakoil' patent. However, it should be understood that the present invention while particularly effective when used in connection with the Sartakoif process, is equally well adapted to any form of surface drying operation,- such as conventional drum drying or the like. The film, or the like, may be collected in any desired manner.

When drying any material upon a heated drying surface, care must be taken to avoid too elevated a surface temperature not'only to prevent injury to the material itself,*but in order to obtain the highest rate of evaporation. If too high a temperature is employed, a layer of steam forms between the material and the drying surface and this layer of steam insulates the material from the heat of the siuface, in turn reducing the rate of evaporation. The most efficient temperature of a drying surface for most fruits and vegetables 1 is approximately from 180 to 220 F. Ii the temperature is much above or below this range the rate of evaporationdecreases. However, in drying some materials otherconsiderations may render it advisable to employ a surface ternperature outside of this specified range.

That portion of the face of the drying drum on which the drying operation is conducted, between the distributor roll and the scraper, is enclosed withina hoodll extending from a point. closely adjacent the scraper to 'and enclosing the point of application of the material such as the distributor roll and the feeder head 71.

I have found that in the drying of fruit and vegetable materials, when fresh pulp having a high water content is first dispersed over a heated drying surface, the moisture evaporates with great freedom, in substantially the same manner as free water. However, as the percentage of moisture in the material is reduced, evaporation occurs less and less freely until when the moisture content is less than approximately 10% evaporation of all or .part of the remaining moisture without injuring the material involves considerable .difllculty. "In order to safely accommoisture, something more than mere heating or reduction in pressure is required.

Also, in drying such a material as fruit or vegetable pulp, evaporation of the liquid component absorbs suflicient latent heat to keep the temperature of the material down to a relatively low and safe point, but this is true only so long as the evaporation occurs rapidly enough to absorb the necessary amount of heat. When the evaporation of moisture from a heated fruit or vegetable particle is too slow to absorb sufflcient latent heat the temperature of the material is raised to substantially the same temperature as the heating medium. Heretofore, 13 this has resulted either in such overheating of the materialas to injure the fresh fruit or vegetable, or it has required drying at a low temperature which in tui'n required a prolonged exposure of the material and corresponding damage.

In the present invention, in order to obtain the desired degree of drying in the shortest possible time without the use of dangerously elevated temperatures or subnormal pressures, pro- 88 vision is made for directing a stream of moisturecollecting air having certain predetermined characteristics alongithe drying surface in contact with the material being dried and in a direction counter to the direction of movement so of such material. The moisture-collecting capacity of this air stream is so controlled and maintained as to turn the above mentioned evaporation factors to advantage in order to accomplish the purposes of the present invention.

The stream of moisture-absorbing air is first heated sufllciently to reduce its relative humidity to a low point, preferably to or less. Inasmuch as the ordinary atmosphere is employed, it will be apparent that the actual amount of heathumidity 40%, in order to reduce. its relative humidity to 10% it must beheated to about 72 F. If the temperature of the air is 32 F. and its relative humidity 90%, it must be heated to approximately 98 F. On the other hand, if the temperature of the air is 90 F. and its relative humidity 40% it must be heated to approximately 142 F. to bring the relative humidity down to 10%. If the temperature of the air is 90 F. and its relative humidity 90% it must be heated to approximately 178 F. The necessary amount of heating required on different days can be readily determined by known methods and varied in accordance with prevailing atmospheric conditions. The heated air stream having a low relative humidity is conveyed through an inlet conduit ii to the drying surface at a point closely adjacent the scraper where the evaporation of moisture from the material is substantially complete, except for a-small remaining percentage which is ordinarily difllcult to remove without injury to the material. However, the water-absorbing capacity of the air resulting from its low relative humidity is such as to rapidly absorb the small amount of moisture remaining in the material at that point and, in this way, maintain active evaporation until the instant when the material is removed from the heated surface. The material is removed from the heated surface as soon as it'has lost the protection against overheating afforded by the evaporating moisture. 7 I have found that a hygroscopic material such,

mg necessary to reduce its relative humidity to In the present invention, as above noted, during approximately the entire last half of the drying operation, as the partially dried material on \the drying surface approaches the knife blade, the

high rate of evaporation is maintained by contact with air at low relative humidity. The heat received by the counter flowing air stream from the heated drying surface prevents cooling of the stream and resulting condensation of the moisture collected thereby. In this way-the relative humidity of the stream is kept below the critical point, approximately 40% in the case of Sartakoff products, until it comes in contact with material on the upper portions of the drum surface, where the material is predominantly liquid and has substantially the evaporation characteristics of free water. Here the relative humidity of the air stream can be increased above the critical point without too greatly reducing the rate of evaporation. As the air stream travels over this predominantly liquid material, although the temperature of the air stream is maintained against lowering by the heat from the drum, it rapidly becomes substantially saturated so that by the time it reaches the distributor roll and is in contact with the material freshly delivered to the drying surface its relative humidity is approximately 95%. This tends to reduce the rate of evaporation during the first part of the drying operation and aids in producing a more constant rate of evaporation of moisture from the material from the time it is first placed on the drying surface until it is removed therefrom.- The moisture laden air is removed from the drying surface through a conduit It.

In order 'to prevent moisture which may condense on the inner face of the hood ll above the drum 5, from dripping on to the top of the drum,

the hood is shaped at that point to provide steeply inclined surfaces ll down which any condensed moisture will flow to gutters l5 which carry it away.

It will be apparent that in passing over the drying surface and absorbing moisture therefrom to be thereby heated to the desired point for the purpose of reducing its relative humidity. If desired, the incoming air can have its temperature raised further by a suitable heating means such as a heating coil It or the like, to reduce its relative humidity still further. The large number of B. t. u.s carried by the vaporized moisture in the moisture-laden air stream are ordinarily sufl'lcient to raise the temperature of the relatively dry. incoming air to the required degree, so that further heating thereof is optional. Means -fan 2| and damper 22.

Obviously, the invention can be variously modified and adapted within the scope of the appended claims.

I claim:

1. The method of reducing the moisture content of a material which when dry is hygroscopic in air having a relative humidity above a certain critical point, which consists in distributing the material to be dried over a drying surface, passing the material on said surface through a drying zone and removing substantially dry material from said surface, passing a stream of moisture removing air over the material in said zone and in a direction counter to the direction of movement of the material through said zone, maintaining the relative humidity oi said air stream below said critical point until said stream is in contact with material still predominantly liquid, and maintaining said current of air in contact with liquid material until substantially saturated.

2. The method of reducing the moisture content of fruit and vegetable material which consists in forming a pulp of the original material, distributing said pulp over a heated drying surface, causing said material to move continuously through a drying zone at a temperature sumcient to reduce the moisture content to a predetermined point, passing a current of moisture removing air through said drying zone over said material in a direction counter to the direction of movement of. said material, maintaining the relative humidity of said air stream below that at which the partially dry hygroscopic material will absorb moisture until said stream is in contact with material predominantly liquid, and then permitting said stream to become substantially saturated.

3. The method of reducing, the moisture content of fresh fruit and vegetable material which consists in dispersing the particles of said material over a heated drying surface in substantially separated condition whereby each particle is subjected substantially directly to the heat thereof, progressively subjecting said particles on said surface to a drying temperature to reduce the moisture content of said particles to a predetermined point, removing the dried particles from the drying surface, simultaneously with the drying operation passing a stream of moisture col-- lecting air having a low relative humidity first over the particles most nearly dry and then progressively over less dry particles and then over fresh material just dispersed on said surface, and maintaining the relative humidity of said air stream below that at which the partially dry hygroscopic material will absorb moisture until said stream is in contact with material predominantly liquid, and then permitting said stream to become substantially saturated.

4. The method of reducing the moisture content of fresh fruit and vegetable material which consists in dispersing the particles of said material over a heated drying surface in substantially separated condition whereby each particle is subjected substantially directly to the heat thereof, progressively subjecting said particles on said surface to a drying temperature to reduce the moisture content of said particles to a predetermined point, removing the dried part1- cles from the surface, and simultaneously with the drying operation passing a stream of air having a low relative humidity first over the material having less than 10% moisture, maintaining the relative humidity of the air stream at less than 40% while in contact therewith, then passing said air stream progressively over less dry particles and then over fresh material just dispersed' on said surface, until said air stream is substantially saturated.

5. The method of reducing the moisture con-' tent of fruit and vegetable material which consists of spreading the material over a moving heated drying surface, passing a stream of air having a low relative humidity first over the material having lessthan 10% moisture, maintaining the relative humidity of the air stream at less than 40% while in contact therewith, then

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