IES80728B2 - Mussel processing - Google Patents

Abstract

A process for preparing mussels comprises removing the byssi from the mussels, placing said mussels in a retaining tank, containing ultraviolet treated, oxygenated salt water with a salinity above the normal threshold for mussels, until such time as they have regrown a small byssus. The water in the retaining tank is preferably oxygenated and has a salinity of 35 parts per thousand and is maintained at 12{C. The mussels are preferably retained in the tank for 60 minutes. The process may include the preliminary steps of cultivating and harvesting the mussels, placing them in a purification tank containing ultraviolet treated salt water followed by brushing cleaning and grading of the mussels. The mussels may subsequently be vacuum packed, cooked in the packing and frozen for storage.

Description

Introduction The present invention is directed towards a process for processing mussels such that following harvesting and purification, the mussels retain their natural juices inside the shell, preserving the freshness and delicate texture of the meat.

The edible mussel Mytilus edulis is an adaptable bivalve mollusc found dispersed around our coastlines. Over the years, new concepts and methods of cultivation have been developed. Due to their adaptability and hardness, Mytilus edulis can be cultivated on the sea bed or on floating structures in which they are suspended from barrels on ropes. Mussels cultivated in this fashion tend to be clean, sharp edged shells and fast growing. This makes them very attractive for processing.

Mussels are filter feeding organisms and these extract food and life support materials from the sea water by forcing water through its gill membranes where such materials are caught on particles of mucous formed by the organisms. The means for forcing water through the membranes are the cilia which beat the water into motion. With each beat of the cilia, an amount of water is put in motion and is immediately replaced with an equal amount at the point of displacement The beating of the cilia sets up a continuous current that moves nutrient-laden waters towards its gill membranes. The mussel performs this function by channelling water into the filtering apparatus by allowing its shell to gapeslightly, thereby exposing an intensive gill structure. It is via this method that the mussels can entrap food and particulate materials on the mucous gill membranes whilst ensuring a constant channelling of water.

Following harvesting, the mussels are attached in clumps by their byssus ο Ο υ : ϋ - 2 threads, which aid to retain water and ensure high local humidity. Once the mussels are separated and debyssed, there is a certain amount of water loss. The function of the debyssing is to improve the appearance of the mussel and enhance cleanliness removing sand and grit. However, the loss of water results in the loss of juices in the mussel meat and the meat tends to deteriorate and become dry with subsequent loss of taste. When the mussel meat within the shell contains water, the water in the shell facilitates even cooking by heating up first and acting as a heating agent which surrounds the meat. It allows for a fresher taste after subsequent reheating if the mussel is cooked and frozen before final use.

It is an object of the present invention to provide a process wherein the water is retained in the meat in the mussel shell.

Statements of Invention The invention provides a process for preparing mussels for consumption including:debyssing the mussels; placing the debyssed mussels in a retention tank containing ultraviolet treated oxygenated salt water which has a salinity that exceeds the normal threshold for mussels, forcing the mussels to filter feed thereby removing particulate contaminants and retaining water; retaining the mussels in the retention tank until such time that a small byss regrows replacing the removed one to seal the mussel to retain the water therein.

This unique process combining oxygen and a salinity of full strength seawater, encourages the mussels to filter feed and to regrow a small byss. This recovers the water loss following debyssing in two ways: increasing the local humidity by causing water to be filtered through the gills and sealing the hole left in the mussel following byss removal.

Preferably the water in the retention tank is oxygenated. The salinity of the water tank is greater than 22 parts per thousand. Preferably, the salinity is in the range of 30 parts per thousand to 40 parts per thousand. Most preferably, the salinity is 35 parts per thousand.

By increasing the salinity in the retention tank, this in turn encourages byssus formation which in turn helps the mussels retain the water filtered by them while in the tank.

In a preferred embodiment, the mussels are retained in the retention tank in order for byss regrowth for at least 30 minutes. Preferably, the mussels are retained in the retention tank for 35 to 120 minutes. Most preferably, the mussels are retained in the retention tank for byss regrowth for 60 minutes. This allows the mussels time to acclimatise to the salinity of the water in the tank.

In a preferred embodiment, the water in the retention tank is 5-15°C. Preferably, the water is 9-15°C. Most preferably, the water in the retention tank is 12°C. Experimental findings demonstrate that this is the optimum temperature range for filter feeding and thus a favourable environment for byssusformation.

The invention provides a process including the preliminary steps of:cultivating mussels by rope suspension and bottom culture; harvesting the mussels; placing the mussels in a purification tank containing ultraviolet treated oxygenated salt water; brushing, cleaning and grading the mussels; and including the subsequent steps after allowing the byss regrowth of:vacuum packing the mussels in a flexible packing to retain the shells closed; cooking the mussels in the vacuum pack until the mussels are fully cooked; cooling the mussels by immersing them in chilled water; freezing; and storing.

Using this process freshly harvested, top quality mussels are purified, vacuum packed and processed with all of the natural juices retained inside the shell. These act as a natural glaze to the meats so that when heated, the frozen shellfish have the same delicate taste as fresh mussels. Market trends for cooked vacuum packed mussels are increasing-on an annual basis because the product is attractive and convenient to consumers. Cooked vacuum packed mussels prepared according to the process deliver a greatly improved product with enhanced organoleptic properties.

In a preferred embodiment, the salinity of the water in the purification tank is greater than 22 parts per thousand. Preferably, the salinity is in the range of 30 parts per thousand to 40 parts per thousand. Most preferably, the salinity is 35 parts per thousand.

Mussels by virtue of their filter feeding acquire particulate materials and microorganisms attached to the mucous of the gill membranes. These shellfish can be rendered suitable for consumption by a purification or depuration process. With the aid of high salinity, the shellfish are forced to filter feed resulting in increased water circulation through the gill membranes. Increased circulation increases the rate of removal of particulate and waste materials from the mussels.

In a preferred embodiment, the water in the purification tank is 5-15°C. Preferably, the water is 9-15°C. Most preferably, the water in the retention tank is 12°C.

In a preferred embodiment, the mussels are placed in the purification tank for 12 to 48 hours. Preferably, the mussels are placed in the purification tank for 12 to 24 hours. Most preferably, the mussels are placed in the purification tank for 12-18 hours. The length of time in the purification tank is dependent on the levels of microorganisms in the sea from whence the mussels were harvested. The higher the levels, the longer the purification process.

In a preferred embodiment, the water in the purification and retention tank is oxygenated and ultraviolet treated. The ultraviolet treatment helps keep the waterpureandfreeofbacteria.— -------- -------- ------- -----------------------------In a preferred embodiment, the mussels are cooked to a core temperature of 72°C by submerging the mussels in the vacuum pack in water at 80 to 100°C for up to 18 minutes. Preferably, the mussels are cooked in water at 90-100°C for to 8 minutes. Most preferably, the mussels are cooked in water at 100°C for 7 minutes. This ensures that the mussels are fully cooked.

In a preferred embodiment, the mussels are frozen by blast freezing at -15°C to 5 30°C.

In another embodiment, microbiological contamination is minimised via the use of ultraviolet treated sea water. io In a preferred embodiment, water loss is minimised by retaining the mussels at a high salinity for a time period allowing the mussels to filter feed and regrow a byss. When the mussel meat within the shell contains water, the water facilitates even cooking. This allows for a fresher taste after subsequent reheating of the mussel is cooked and frozen before the final use. The vacuum packed mussels maintain the same taste of the succulent moist meat of fresh mussels.

Detailed Description of the Invention Fig. 1 is a flow diagram of the mussel treatment plant.

Fig. 2 is a plan view of portion of the plant.

Fig. 3 is a side view of portion of the plant.

Referring to the drawings there IsfflustratecTa mussef treatment “plant for performing the process according to the invention indicated generally by the reference numeral 1. The plant 1 comprises a mussel container storage station 2 and purification tank 3 and then a mussel handling portion indicated by the letter M comprising a hopper 4 for a feed conveyor 5 feeding to a brush cleaning machine 6 having an outlet hopper containing a shaker grader 7 with a screen cloth above a pair of feed conveyor elevators 8 which in turn feed into a debyssing machine 9. The debyssing machine 9 delivers to an inspection conveyor 10 mounted on a platform 11 feeding directly to a retention tank 12 mounted within which is a washer elevator 13 feeding a transfer conveyor 14 which in turn feeds to a further inspection table 15 and a packing station 16 having a vacuum packer 17. The vacuum packer 17 feeds a continuous belt 18 which delivers directly to a cooker 20, chiller 25, freezer 30 and storage 35.

Within hours of harvesting, the mussels arrive and are placed in containers 2, before being lowered into the purification tank 3 containing oxygenated ultraviolet treated seawater where they spend 12 to 24 hours. To determine the length of time that mussels should spend in the purification tank, the sea water from where they are harvested is tested periodically for microbial presence. Certain categories of mussels require 48 hours depuration. From here, they are delivered from the hopper 4 onto the feeding conveyor 5 and to the brush cleaning machine 6 which brushes and cleans the mussels when they are delivered to the grader 7. All mussels under 15 mm are rejected. The mussels are then conveyed on the conveyors 8 to the debysser 9 where the byss will be removed. From there they are conveyed at an inspection conveyor where any mussels having open or broken shells are removed at the platform 11.

Once the debyssing has occurred and the long threads which usually attach the mussels to the rock on the seabed are removed, the life of the mussels is considerably shortened. The mussels at this stage also will have lost a considerable amountofwater. It is therefore neeessary to store themin an environment wherein they can take in water into the mussel meat again. The mussels are placed in the retention tank 12 which contains oxygenated ultraviolet treated salt water. The water is purified and oxygenated and radiated with ultraviolet light to kill any microbiological organisms present This reduces the possibility of microbiological contamination of the shellfish. The salinity or salt concentration of the water in the retention tank is such that it exceeds the normal threshold of salinity for mussels. The normal salinity levels that mussels prefer is 22 parts per thousand. When the salinity is too low, shellfish will not open and filtration does not take place. By placing the mussels in oxygenated salt water with a salinity that exceeds normal i.e. greater than 30 parts per thousand, they are forced to filter feed in order to maintain homeostasis and osmotic potential. Following the filter feeding, increased circulation of water within the mussel increases the rate of removal of waste materials from the mussel and also any contaminants, for example, sand or dirt. This has a combined effect of reinstating the water in the mussel meat and also removing waste materials and reducing the possible spread of disease. High salinity levels can encourage byssus formation which in turn can help retain the water filtered by them while in the tank. The mussels are thus retained in the retention tank for a time period long enough for them to regrow the removed byss sufficiently to seal the hole left following the previous debyssing. The temperature of the salt water in both the purification and retention tank is between 10 and 12°C. The time period for the mussels to regrow a byss is considered to be 30-60 minutes thus despite the amount of mussels in the tank, this buoyancy enables the shelf to gape slightly exposing the gill membrane allowing them to filter feed. As the mussels start to filter feed and take in water, they sink to the bottom where a conveyor 14 conveys the mussels to an inspection table 15 where they are again inspected for broken shells and open mussels.

They then go through a packing process 16 and then they are vacuum packed in flexible envelopes. The vacuum packed mussels are then placed on a continuous conveyor belt 18 where they are conveyed into a cooker 20 containing water is at a temperature of 80-100°C and they are maintained there for 4 minutes such that the mussels are fully cooked. The mussels are cooled by being conveyed into chilled water in the chiller 25 and then they are frozen by blast freezing at -15°C to -30 C before being delivered to storage 35.

Table 1 is a brine conversion table used to alter the salinity of the retention tank.

TABLE 1 35kg Bag 15Kg Bag PP Thousand 5°C 10°C 15°C Species 72L 360L 35 water 80L 400L 31 90L 450L 28 94L 467L 27 minimum species 100L 500L 25.5 minimum 123L 615L 20.5 minimum 130L 650L 29.5 minimum 1.0285 1.028 1.027 Full sea 1.026 1.0255 1.0245 Lobster 1.023 1.0225 1.022 Crab 1.0225 1.022 1.021 Mixed tank 1.021 1.0205 1.020 Native oyster 1.017 1.017 1.016 Pacific oyster 1.016 1.016 1.015 Mussel The invention is not limited to the specific embodiments hereinbefore described, 2 0 which may be varied in detail within the scope of the claims.

Claims (5)

1. A process for preparing mussels for consumption including:debyssing the mussels; placing the debyssed mussels in a retention tank containing ultraviolet treated oxygenated salt water which has a salinity that exceeds the normal threshold for mussels, forcing the mussels to filter feed thereby removing particulate contaminants and retaining water; retaining the mussels in the retention tank until such time that a small byss regrows replacing the removed one to seal the mussel to retain water therein.

2. A process according to claim 1, including the preliminary steps of:cultivating mussels on by rope suspension and bottom culture; harvesting the mussels; placing the mussels in a purification tank containing ultraviolet treated oxygenated salt water; brushing, cleaning and grading the mussels; and including the subsequent steps of:11 vacuum packing the mussels in a flexible packing to retain the shells closed; cooking the mussels in the vacuum pack until the mussels are 5 fully cooked; cooling the mussels by immersing in chilled water; freezing; and storing.

3. A process as claimed in claim 12, wherein the salinity of the water in the purification tank is greater than 22 parts per thousand.

4. A process as claimed in any of the preceding claims, wherein water loss is minimised by retaining the mussels at a high salinity for a time period allowing the mussels to filter feed and regrow a byss. 20

5. A process for preparing mussels for consumption substantially as described herein.