BACKGROUND

The invention relates to machine-peeling shrimp after freezing them in a brine solution.

U.S. Pat. No. 2,778,055 to F. S. Lapeyre et al. describes an automated shrimp-peeling machine for removing the heads and shells of raw shrimp. The peeling machine removes the shells and heads with an array of counter-rotating peeling rollers that pinch the shells and heads to separate them from the shrimp meat. Shrimp peelers based on the roller-peeling principle have been used for years to peel shrimp. The machines work well, but some unpeeled shrimp still make it through the peeling process. And shrimp meat is sometimes pulled from the main shrimp body along with the shells.

SUMMARY

One method of peeling shrimp embodying features of the invention comprises:

(a) freezing shrimp in a brine solution; (b) thawing the brine-frozen shrimp; and (c) peeling the thawed shrimp in a mechanical peeling machine to remove shells.

In another aspect, a system for preparing shrimp for machine-peeling embodying features of the invention comprises a brine freezer freezing only the outer shrimp meat and not the cores of the shrimp with a brine solution, a thawer thawing the brine-frozen shrimp, and a conveyor belt system conveying shrimp continuously into and through the brine freezer to and through the thawer.

Another version of a system for preparing shrimp for machine-peeling embodying features of the invention comprises a brine freezer completely freezing the shrimp through to the core with a brine solution, a thawer thawing only the outer layer of the shrimp meat of the brine-frozen shrimp, and a conveyor system conveying shrimp continuously into and through the brine freezer to and through the thawer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a first peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp.

FIG. 2 is a flowchart of a second peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp. FIG. 3 is a flowchart of a third peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp.

FIG. 4 is a flowchart of a further peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp.

FIG. 5 is a flowchart of a first peeling sequence especially, but not exclusively, for block-frozen raw shrimp.

FIG. 6 is a flowchart of a second peeling sequence especially, but not exclusively, for block-frozen raw shrimp.

FIG. 7 is a flowchart of a first peeling sequence especially, but not exclusively, for block-frozen or individually quick frozen (IQF) raw shrimp.

FIG. 8 is a flowchart of a second peeling sequence especially, but not exclusively, for block-frozen or IQF raw shrimp.

FIG. 9 is a flowchart of a first peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp.

FIG. 10 is a flowchart of a second peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp.

FIG. 11 is a flowchart of a third peeling sequence especially, but not exclusively, for fresh, never frozen raw shrimp.

FIG. 12 is a flowchart of a first peeling sequence especially, but not exclusively, for IQF (brine-frozen) headless raw shrimp.

FIG. 13 is a flowchart of a second peeling sequence especially, but not exclusively, for IQF (brine-frozen) headless raw shrimp.

FIG. 14 is a block diagram of a peeling-preparation system capable of performing pre-peeling steps as in the peeling sequences of FIGS. 1-13.

FIG. 15 is a block diagram of another version of a peeling-preparation system capable of performing pre-peeling steps as in the peeling sequences of FIGS. 1-13.

DETAILED DESCRIPTION

The following definitions apply to all the flowcharts of FIGS. 1-13. Supported by the definitions, the flowcharts themselves describe each process in sufficient detail to enable one of ordinary skill in the art to practice the inventions. Raw material means raw shrimp used as the starting material. The headline of each figure further defines the raw shrimp as: (a) fresh, never frozen (including thawed from frozen); (b) frozen in blocks; (c) IQF (individually quick frozen), i.e., in brine or not; and (d) IQF (brine frozen), i.e., individually quick frozen in brine.

PPTS stands for Pre-Peeling Treatment System and refers to flowing shrimp in bulk through a conduit with a narrowing cross section that causes an increase in flow speed, which subjects the shrimp to hydrodynamic forces that help separate head and shell from shrimp meat. An example of such a PPTS device is disclosed in U.S. Pat. No. 8,801,507. The disclosure of that patent is incorporated into this description by reference.

Dehead means remove the heads from shrimp by means other than PPTS, such as by hand or a mechanical device.

Size Grade means to sort the shrimp into various grades by size.

Thaw means to unfreeze the shrimp from a frozen state to a state in which the shrimp meat is not frozen. One way to thaw is with a fresh-water rinse, which also tends to make the shell less slippery and easier to peel. Rinsing may also be performed as a separate step after thawing. Thawing includes complete thawing through the shrimp's core and partial thawing, e.g., thawing only of the outer layer of the shrimp.

Peel means to remove residual shells and heads from shrimp meats in bulk with an automated mechanical peeling machine such as the peeling machine disclosed in U.S. Pat. No. 2,778,055. The disclosure of that patent is incorporated into this description by reference.

Brine Freeze means to subject a batch of shrimp to a cold brine solution whose temperature is below 0°C to freeze the shrimp individually completely through or only at the outer surface. Brine freezing is conventionally done for the purpose of freezing the shrimp for storage or transport. As such, brine freezing conventionally freezes the shrimp completely through. Brine freezing followed by thawing also reduces the strength of the bond between the shell and the shrimp meat and makes it more consistent, independent of the molt stage of the shrimp. It also makes the shell less slippery and more consistently so. As such, brine freezing improves subsequent roller peeling for more thorough shell removal with less meat breakage.

Brine freezing only at the outer surface followed by equally rapid thawing provides this peelability benefit without the disadvantages of conventional complete freezing and subsequent protracted thawing. Brine freezing for less than five minutes, even for as short as a fraction of one minute, can be as effective in aiding peeling, and brine freezing only the surface layers of shrimp is more energy efficient and much faster than brine freezing shrimp solid. The brine-frozen shrimp can be thawed immediately after the brine-freezing surface treatment. And the short brine-freezing and thawing times are more compatible with a continuous process flow. This makes an integrated freezing and thawing system much more viable. When shrimp are frozen through, they have to then be thawed through as well, which requires heat removal during freezing and then at least as much, and typically more, heat addition. When thoroughly brine-frozen shrimp are rapidly thawed in water so that their meat is still largely frozen, they do not peel well even though the shell-meat bond has been weakened. That's because roller peeling requires the underlying material that the rollers are working against— in this case the shrimp meat— to be deformable so that the rollers can gain purchase to pinch off the shell. The only way to avoid having to thaw fully is to not freeze fully in the first place. So partial brine freezing, which is not useful for freezing material for shipping, is effective in preparing shrimp for peeling. Another advantage of rapid brine freezing is less cellular damage for a firmer, better final product. Multiple freezing cycles are bad, especially slow ones, because the slower the freezing the greater the opportunity for large ice crystal to form in the cells, causing cell rupture and then loss of firmness. Water then drains out more easily horn the ruptured cells themselves, not only horn between them, resulting in yield loss and more dehydration. And more freezing cycles cause even more yield loss and more dehydration. So, by subjecting the shrimp to a partial, surface-spedfic brine freeze, the interior meat doesn't experience a freeze cycle, allowing it to be frozen through only once (at pack-out).

Packout refers specifically to the packaging of peeled shrimp but includes any other final processing steps required to ready the peeled shrimp for packaging.

Mature means to allow thawed or never frozen shrimp to rest in cold water, an ice- water mixture, or a solution, e.g., of water and other ingredients at a temperature ranging horn about 0°C to about 15°C for a period ranging from about 1 hour to about 36 hours for the purpose of allowing time for the bond between the shells and the meat to weaken enough to enable effective and easier peeling and head removal. Maturing may also saturate the cells, as well as the spaces between, and make the shrimp more resilient during subsequent processing. Maturing shrimp in water, an ice-water mixture, or a solution also equalizes the shrimp to the same moisture level.

A system for preparing shrimp for machine peeling by performing pre-peeling steps as in the processes of FIGS. 1-13 is shown in FIG. 14. The peeling-prep system 20 conveys unfrozen shell-on shrimp through a brine freezer 22. The conveyor system can be a belt conveyor including a single conveyor belt or a series of conveyor belts continuously conveying shrimp through the peeling-prep system. The brine freezer 22 freezes the incoming shrimp at a temperature Tsi to brine-frozen shrimp at a lower temperature Ts2 at the output. The brine freezer 22 depicted in FIG. 14 is an immersion freezer in which the shrimp on the conveyor belt are submerged in brine. As an alternative, the brine freezer can be a rainfall chiller, in which the shrimp on the belt are rained on by brine. The freezer 22 is also shown as a zone freezer, in which the freezer is composed of individual freezing zones 24A-E. Chilled brine fluid is pumped into the freezer 22 at a temperature TBI. The brine flows through the zone chambers 24A-E in a counterflow direction opposite to the conveying direction 26. The counterflow ensures that the temperature of the brine is coldest at the output of the freezer and is progressively warmer in each zone closer to the input (TBI < TB2 < TB3 < TB4 < TBS < TB6). In that way the brine temperature drops in controlled increments as the shrimp are progressively chilled in the freezer's zones. If an immersion freezer is used, the conveyor belt could follow a roller-coaster path that dives at the entrance to each zone and rises just before exiting each zone 24A-E. Pumps between each zone draw brine out of a zone and pump it into the freezer at the next zone upstream. Spent brine exiting the brine freezer 22 at a temperature TB6 is redrculated back to a brine reservoir 28.

The brine-frozen shrimp exiting the brine freezer 22 at a temperature Ts2 are conveyed into a thawing station, thawer 30. Like the freezer 22, the thawer 30 is zoned and uses a counterflow of warmer brine to thaw the shrimp. Also like the freezer 22, the thawer 30 can be an immersion thawer or a rainfall thawer, as two examples. The temperature in each thawing zone is progressively lower horn the shrimp output of the thawer to the input (TB7 > TB8 > TB9 > TBIO > TBH > TBU). In that way thawing can be more precisely controlled. Thawing can be complete, i.e., through the shrimp body horn outer surface through the core, or partial, i.e., just through the outer layer of the shrimp with the core still frozen. The brine exiting the thawer 30 at a temperature TBU passes through a heat exchanger 32, which chills the brine to a temperature TBI for the brine freezer 22. Any brine that overflows the thawer 30 goes down the drain. Spent brine from the freezer 22 is

reconstituted to the proper salinity in the reservoir 28. Salt and make-up fresh water replacing brine lost dining freezing and thawing are mixed with the spent brine to maintain the desired salinity level of the brine. The brine warms up in the reservoir to a temperature TB7 for use in thawing.

The thawed shrimp exiting the thawer 30 at a temperature Ts3 are conveyed by the conveyor belt to a rinser 34. Fresh water pumped into the rinser 34 washes slime and other slippery material from the thawed shrimp. Depending on the temperature of the rinse water, the temperature Ts ₄ of the shrimp exiting the rinser 34 may be greater or lower than the entering temperature Ts3. But the rinser 34 could be used to thaw the shrimp further if the temperature of the rinse water is higher than that of the thawing shrimp at the temperature Ts ₃ entering the rinser. Spent rinse water goes down the drain. The shrimp exiting the rinser 34 are then conveyed to the roller peeling machinery for peeling. By conveying the shrimp through a brine-freezing treatment that freezes only the outer shrimp meat and not the core of the shrimp meat, through a thawing treatment that thaws the partially brine-frozen shrimp, and a rinsing station that rinses the shrimp, the entire integrated process can be performed rapidly and continuously without any time-consuming batch operations. And the multizone freezers 22 and thawers 30 could be replaced with shorter, single-zone freezers and thawers to freeze and thaw only the outer layers of the shrimp. And in some cases the thawing process can be carried out by the rinser 34 alone.

Such an abbreviated peeling-preparation system is shown in FIG. 15 without freezer or thawer zones and with no counterflow. In this version, unfrozen (thawed from frozen or fresh, never frozen) shrimp are conveyed into and through a brine freezer 40, such as an immersion brine tank filled with a brine solution at a temperature of about -20°C to about -10°C or a rainfall chiller raining chilled brine onto the shrimp. The shrimp are partially frozen in the brine freezer 40 with their outer layers frozen hard while their cores remain unfrozen. The partially brine-frozen shrimp are then conveyed through a rainfall rinser 42 that also acts as a thawer by thawing the shrimp with fresh warmer water as it rinses slimy matter from the shrimp. The thawed shrimp are then conveyed to a machine peeler for peeling. The shrimp are conveyed continuously through the system by a belt conveyor system 43. A brine refrigeration system 44, such as a heat pump, draws brine from the brine freezer 40, chills it, and recirculates it via pipes 45 to the freezer. The fresh water used in the rinser-thawer 42 is redrculated via pipes 46 through the condenser in the brine refrigeration system 44 to warm the spent rinse water cooled by the thawing shrimp with otherwise wasted heat generated in chilling the brine. So the system of FIG. 15 is a high-efficiency, low- energy-use system.

FIGS. 1-13 represent various versions of processes for machine-peeling brine-frozen shrimp. It's possible that raw material other than that mentioned in the headline of each flowchart can be successfully peeled by the process shown in the flowchart.