Butchering – Tenderizers
Reexamination Certificate
1999-07-02
2001-05-01
Little, Willis (Department: 3643)
Butchering
Tenderizers
C426S058000, C426S238000
Reexamination Certificate
active
06224476
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to certain embodiments for processing of meat or other food products by shock waves, preferably plasma generated by capacitive discharge between two electrodes.
REVIEW OF THE RELATED TECHNOLOGY
As explained in the copending application of John Long, filed on even date herewith and entitled “Continuous Shock-Wave Food Processing With Shock Wave Reflection”, which is entirely incorporated herein by reference, meat can be tenderized and at least partially sterilized by shock waves (acoustic or pressure pulses) from an explosions caused typically by a chemical explosive charge or a capacitive discharge between two electrodes such as shown in the John Long U.S. Pat. Nos. 5,273,766 and 5,328,403, and pending applications, two of which correspond to WO98/38875 and WO98/54975. A shock wave travels outwardly 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 from an explosion is brief but has an appreciable width, 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.)
U.S. Pat. Nos. 5,397,961 and 5,368,724 in the names of Ayers et al disclose a shock wave reflector reflecting a shock wave originating from a spark between electrodes. The diverging shock wave from the approximately point-source electrode gap expands spherically and encounters reflective surfaces which are “parabolic” or “hemispherical” (see column 3, lines 60 or 61 of the '724 patent) or “concave” (see column 4, line 30 of the '961 patent). The shock wave is apparently converted to a plane wave front which then is funneled into a horn-shaped “concentrator” to increase its intensity. These patents do not disclose any focussing, and do not relate to the treatment of meat to improve meat for consumption.
In a preferred embodiment according to Long '766 and '403, the meat was placed in evacuated 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 meat twice due to the reflection. (The meat and the enclosing bags, having an acoustic impedance close to that of water, do not appreciably reflect the shock pulse.)
This system works very well in tenderizing and at least partly sterilizing the meat lined around the shell, but it has some drawbacks. Importantly, this system is inherently a batch operation, and the equipment is expensive. A stainless steel hemisphere four feet 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 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 in contact with the meat. This takes time and uses a great deal of water.
Morever, the explosive force in the aforementioned embodiments is not balanced. The geyser of blast gases, steam, and spray emanating from the top of the hemisphere causes a large reaction force which drives the hemisphere downward, and this must be resisted by large springs, dashpots, and so on. A special blast-shield dome is needed to absorb the force of the geyser.
Placing meat into protective plastic bags can cause problems because any air bubble which gets packed into 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). The bubble will focus the shock wave 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 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 thickness 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 width 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 intensity of a spherical wave falls off approximately as the cube of the radius (which corresponds to the distance from the 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, partly due to the gas bubble produ
Ayers Richard A.
Long John B.
Browdy and Neimark
Hydrondyne Incorporated
Little Willis
LandOfFree
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