Food or edible material: processes – compositions – and products – Direct application of electrical or wave energy to food... – Involving wave energy of the sonic or pulsating type
Utility Patent
1999-07-02
2001-01-02
Bhat, Nina (Department: 1761)
Food or edible material: processes, compositions, and products
Direct application of electrical or wave energy to food...
Involving wave energy of the sonic or pulsating type
C099S451000, C099SDIG014, C422S128000, C452S141000
Utility Patent
active
06168814
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the treatment of meat by shock waves to effect tenderization and/or the killing of microorganisms.
REVIEW OF THE RELATED TECHNOLOGY
Meat can be tenderized and at least partially sterilized by shock waves (acoustic or pressure pulses) from explosions caused typically by a chemical explosive charge or a capacitive discharge between two electrodes, such as shown in the U.S. Pat. Nos. 5,273,766 and 5,328,403 to John Long, and ending applications. A shock wave travels outward from the explosion site at the speed of sound (or somewhat higher in the case of high-intensity shock waves) and, like an audible sound echoing from a wall, will reflect from a shock-wave reflective surface.
The condition for reflection of a shock wave is that the speed of sound, which varies depending on the medium through which it travels, changes at an interface between two media. A pressure wave travels in water at about 1500 meters per second; the same wave travels in stainless steel at 5800 meters per second, nearly four times faster. This difference in the speed of sound is close to the difference in speed for shock waves, which are basically high pressure sound waves; they propagate by the same mechanism as sound does, but are sharp pulses and typically have a much higher sound intensity or pressure rise (sometimes called “overpressure”) than most sounds.
When a sound or shock wave in water encounters a steel surface, most of the wave is reflected away from the surface because of the difference in speed (also referred to as an “acoustic impedance mis-match”), with only a small portion passing into the steel. In the aforementioned related technology, the reflection of shock waves from a thick steel surface was used to increase the intensity of the shock pulse. The pulse of the shock waves from an explosion is brief but has an appreciable length, and when the pulse is reflected from steel it passes through itself, increasing the shock wave pulse intensity. (The same effect is seen at a seawall, where ocean waves reflecting from the wall splash to a greater height up the wall than they reach in open water.)
In a preferred embodiment according to Long '766 and '403, the meat was placed in plastic bags which were lined along the bottom of a hemispherical steel shell, the shell was filled with water, and an explosion was set off in the geometrical center. The shock wave travelled outward to reach all the meat at roughly the same time and hit the meat with roughly the same overpressure or shock wave intensity, passing through the packaging film and meat twice due to the reflection from the steel shell. (The meat and the enclosing bags, having an acoustic or mechanical impedance close to that of water, do not appreciably reflect the shock pulse.)
This embodiment works very well in tenderizing and at least partly sterilizing the meat lined along and adjacent the inner wall of the shell, but it has some drawbacks. Importantly, this embodiment is inherently a batch operation, and the equipment is expensive. A stainless steel hemisphere four feet in diameter and two inches thick is not cheap, and the equipment needed for moving blast shields, water changers, and so on is complex and costly. Packing and removing the meat is slow, and further delays are mandated by safety concerns; workers should not load the hemisphere while the explosive is rigged, for example.
Another drawback is that the water is blown upwardly out of the hemispherical shell by the explosion and must be replenished. In the case of chemical explosives, it is preferable to drain off any remaining water and replace it with fresh water which is untainted by chemical by-products of the explosion, even through such water does not even come directly into contact with the meat. This draining and replenishing takes time and uses a great deal of water.
Also, the explosive force in the aforementioned embodiment is not balanced. The geyser of blast gases, steam, and spray out the top of the hemisphere causes a large reaction force which drives the hemisphere downwardly, and this must be resisted by large springs, dashpots, and so on, this additional equipment also being expensive. A special blast-shield dome above the shell as in Long U.S. Pat. No. 5,841,056 is needed to absorb the force of the geyser.
Placing meat into protective plastic bags can cause problems because any air bubble which remains in the bag along with the meat will act as an acoustic “lens”, focusing the shock wave (this is similar to the converging-lens effect of a water droplet with light) onto the meat just on the other side of the bubble, causing a very high local pressure which can “burn” the meat. The heat so generated will often also burn a hole in the bag causing the plastic bag to rupture.
The placement of the meat against or in near adjacency to the surface of the shock-wave reflective steel is the root of some of the difficulties with previous embodiments as discussed above, and such placement has limitations which prevent any substantial improvement. The width of the layer of meat which can be tenderized is limited by the duration of the shock pulse, because if all the meat is to be subjected to intensity doubling then the thickness of the shock pulse must be at least twice the thickness of the meat, so that the pulse intensity will be doubled throughout the thickness of the meat. If the pulse is of very short duration, its trailing edge will have passed into the meat layer just as the leading edge is reflecting from the steel, and only the portion of meat closest to the steel will experience the doubled shock intensity; the rest will undergo two passes of the non-doubled shock wave. The width of the shock pulse in meters is roughly 1500 m/s divided by the pulse duration in seconds.
Limiting the thickness of meat means that the size of the hemisphere must be increased if each batch of meat to be treated is to be large enough that the overall processing rate is not too slow. But increasing the hemisphere diameter means that the shock pulse will be weaker, since the pressure intensity of a spherical wave falls off approximately as the cube of the radius (which corresponds to the distance from the source or sources of the explosion).
SUMMARY OF THE INVENTION
If the intensity doubling of the earlier embodiments were not insisted on, then the layer of meat could be spaced further away from the shock-wave reflective inner surface of the hemispherical shell, and the greater intensity of the shock wave would make up for the intensity doubling. If the meat were moved inwardly by about 29% of the hemisphere radius (precisely, 1.000 minus 0.707) then the single-pass shock wave intensity would be just as great as the doubled intensity at the inner surface of the hemisphere, even if the explosion energy were not increased. (The shock wave would pass outwardly through the meat and then, after reflection from the steel surface, pass back inwardly through the meat.) This shows that placing the meat directly against or closely adjacent a reflective surface is not essential.
However, the problem then arises as to how the meat can be supported against moving away from the explosion. The present invention employs a container for the meat which, unlike thick stainless steel, has as little reflectivity as possible so that the shock wave passes through it freely. The container can be made “acoustically transparent”, i.e. with a mechanical or acoustical impedance approximately the same as water, so that a sound wave or a shock wave will pass through the container without being significantly diverted in direction or delayed in passage.
There are several ways to make a container acoustically transparent. One is make the container of wires, which sound (and a shock wave) can pass around, but a wire container will not in all cases adequately support the meat, and depending on the size of the wires or rods from which it is formed will interfere with the shock wave. A preferred way, though, is to make the container of a material having the
Bhat Nina
Browdy and Neimark
Hydrodyne Incorporated
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