EP0425636A1

EP0425636A1 - Food dispensing method and apparatus and metering device therefor

Info

Publication number: EP0425636A1
Application number: EP19900907256
Authority: EP
Inventors: Richard Sperring; Malcolm Shipway; Roger 51 Thicket Mead Midsomer Norton Lambert
Original assignee: Courtaulds Films and Packaging Holdings Ltd; Corrugated Products Ltd
Current assignee: Corrugated Products Ltd
Priority date: 1989-05-19
Filing date: 1990-05-18
Publication date: 1991-05-08
Also published as: GB8911631D0; GB2231624A; JPH03506017A; WO1990014270A1; AU5633290A; GB2231624B

Abstract

Un appareillage pour mesurer une quantité prédéterminée de nourriture aseptisée réduite en poudre et conditionner ceci dans un emballage stérilisé à l'avance comprend un réservoir pressurisé (7) pour la nourriture, le réservoir étant relié à un dispositif de mesure (10), via une valve (9). Une orifice d'émission (16) du dispositif de mesure (10) est connecté via une valve de contrôle (12) à une tête de remplissage (13) par laquelle l'emballage est rempli. Le dispositif (10) comprend un piston (14) mobile dans un cylindre qui entraîne la nourriture dans le cylindre ou l'en expulse, le piston (14) étant mu par les différences de pression entre ses deux faces opposées, la pression vers la face arrière du piston (14) étant fournie par un liquide stérilisé à une pression plus basse que celle du réservoir (7), de sorte qu'en fermant la valve (9) et en ouvrant la valve (12), la nourriture est expulsée du cylindre. La course du piston est contrôlée par un système de contrôle pré-régulable qui vérifie l'approvisionnement en liquide stérilisé vers la face arrière du piston (14).Apparatus for measuring a predetermined quantity of aseptic food reduced to powder and for packaging this in a sterilized package in advance comprises a pressurized tank (7) for the food, the tank being connected to a measuring device (10), via a valve (9). An emission orifice (16) of the measuring device (10) is connected via a control valve (12) to a filling head (13) by which the package is filled. The device (10) comprises a piston (14) movable in a cylinder which carries food into the cylinder or expels it, the piston (14) being moved by the pressure differences between its two opposite faces, the pressure towards the rear side of the piston (14) being supplied by a liquid sterilized at a lower pressure than that of the reservoir (7), so that by closing the valve (9) and opening the valve (12), the food is expelled of the cylinder. The stroke of the piston is controlled by a pre-adjustable control system which checks the supply of sterilized liquid to the rear face of the piston (14).

Description

FOOD DISPENSING METHOD & APPARATUS AND METERING DEVICE THEREFOR

This invention relates to the dispensing of food, and especially to the dispensing of food containing particulate matter in an aseptic form for packaging in a pre-sterilized pack.

Recipe dish quality foods for purchase by consumers are becoming more commonplace. These foods are commonly sold from a refrigerated cabinet in a frozen or chilled form, ready for sale. Unfortunately, the temperature in these refrigerated cabinets can change without customers realising that it has occurred, and these changes in temperature can be sufficient to cause the food to become unfit for consumption due to bacteria in the food becoming active.

Tinned food, of course, requires no refrigeration, but it has to be heated in a sealed tin to sterilize the contents of the tin. Because the center of the contents of the tin must be heated for at least 150 seconds to a temperature of the order of 121°C, the outside of the tin has to be heated to a much higher temperature and for a much longer time. Unfortunately, this can cause any particulate matter in the food, such as lumps of meat or vegetables, to break up, so the contents of the tin become less visually appealing and appetizing when served from the tin.

A new technology for the high temperature sterilization of food has been developed involving the "ohmic heating" principle in which heat is internally generated in foods by passing an electric current through them as they travel through a vertical column under pressure. A major advantage of this process is that it enables solid materials in the foods to be heated as quickly as liquid materials therein, so the process provides a high temperature/short time technique for processing foods containing particulate materials. Because the particulate materials are not subjected to long heating times, they do not break up as has been the case with previously proposed sterilizing methods.

In the ohmic heating process the necessary sterilization temperature can be achieved in a very short time. Due to its uniform effect, the ohmic heating process allows far higher Fo values to be applied without consequent product damage than can be achieved using normal canning techniques. The food is rapidly cooled after sterilization and it is then passed to storage tanks from which it can be supplied to a filling head and put into pre-sterilized packages.

Most particulate foods can be ohmically processed, and because of the comparatively gentle nature of the process, all foods, especially fish and vegetables, retain excellent flavour and nutritional values, a firm texture and minimum particle breakdown following ohmic processing. The quality of the processed food is comparable to that of fresh chilled recipe dishes but with the added benefit of a long shelf life due to the absence of micro-organisms. Ohmically processed food packaged in a sterilized pack can, for example, have a shelf life of up to two years with no refrigeration.

As the ohmic heating process has to be operated under pressure, the aseptic processed food has to be stored in a vessel under pressure, so it cannot be dispensed using known packaging equipment. It has therefore been necessary to use two storage tanks connected by a changeover valve. Thus, while one tank is being filled with processed food at a pressure of say four bar (60 p.s.i.), the pressure in the other filled tank can be reduced to a dispensing pressure of say one bar (15 p.s.i.). Duplication of the storage tank facility however doubles the capital cost, and the use of large storage tanks also suffers from the disadvantage that the material stored in a fully filled tank tends to settle out into different stratae if allowed to stand for long periods. This makes drawing off food with a representative sample of the various ingredients of the recipe very difficult as only food in the strata at or adjacent the tank outlet will be dispensed, there being no control over the consistency of the food actually put into the sterilized package.

Another problem with packaging under pressure foods including particulate materials is that sometimes there can be a build up of the particulate materials at the outlet nozzle of the filling head. Such build ups can clear suddenly, thereby creating possibly another inconsistency in the makeup of the food actually put into the sterilized pack.

It is an object of the present invention to overcome or substantially reduce the above discussed disadvantages. According to one aspect of the invention, there is provided apparatus for metering a predetermined quantity of aseptic food containing particulate matter into a pre-sterilized packaging, the apparatus comprising a pressurizable storage tank for the aseptic food to be dispensed and packaged, said tank being connected to a valve-controlled inlet of a metering device, the metering device having an outlet connected to a fill head, the output of the outlet being controlled by a valve, the metering device further comprising a cylinder and a cooperating piston so that food under pressure from the storage tank is forced into the cylinder on opening the inlet valve thereto to cause the piston to retract, the metering device also including means for supplying a sterilized fluid to the rear of the piston and maintaining said fluid at a pressure slightly less than that in the storage tank whereby on opening the said outlet connected to the fill head and closing the inlet valve to the cylinder, the piston is moved along- the cylinder to expel food therefrom, the length of the expelling stroke of the piston being controlled by pre-settable control means operably associated with the means for supplying the sterilized fluid to the rear of the piston.

The contents of the storage tank are preferably maintained at a pressure of substantially four bar, and the sterilized fluid, preferably steam, is supplied to the rear of the piston at a pressure of approximately 3.5 bar. Sterilized air could however be used.

Preferably the piston retracts fully on opening the inlet valve to the metering device.

In the preferred embodiment, the piston has a shaft extending rearwardly therefrom, the pre-settable control means including adjustable limit switches operable to sense the position of the shaft on movement of the piston during its return stroke whereby the supply of fluid under pressure to the rear of the piston is cut off when the shaft reaches a pre-set position. Conveniently, a trigger is mounted on the shaft to cooperate with the limit switches preferably being slidable and disposed alongside the shaft. Altering the position of the limit switches enables the stroke of the piston to be varied and thus the output from the cylinder can be accurately pre-set.

The supply of sterilized fluid to the rear of the piston is preferably controlled by a valve, operation of this valve, and that of the fill head outlet valve and the metering device inlet valve being controlled by central control means, for example a computer.

In a preferred embodiment, the piston has an annular groove around its periphery, the groove cooperating with the cylinder wall to provide a steam barrier or seal when steam is supplied thereto.

According to a further aspect of the invention, there is provided a method of metering a predetermined quantity of aseptic food containing particulate material from a storage tank under pressure to a pre-sterilized package, the method comprising the steps of opening a first valve to admit food from the storage tank into a metering device comprising a piston reciprocable in a cylinder whereby the piston is forced back by the food under pressure, a sterilized medium being supplied to the rear of the piston at a pressure less than that in the storage tank; subsequently closing a valve to cut off the further supply of food to the cylinder; and then opening a second valve downstream of the metering device whereby the piston is forced back under the pressure of the sterilized medium to expel food from the cylinder, the length of the return stroke of the piston being - 6 -

controlled by pre-settable control means whereby a predetermined volume of food is dispensed from the metering device to the pre-sterilized package.

According to yet another aspect of the invention, there is provided a metering device for dispensing a predetermined volume of a foodstuff containing particulate matter, the foodstuff being supplied under pressure to the device in a sterilized condition, the device comprising a piston reciprocable in a cylinder, a foodstuff inlet to the cylinder controlled by a valve, a foodstuff outlet from the cylinder, means for supplying a sterilized medium under pressure to the rear of the piston, the supply of said sterilized medium being controlled by a valve and pre-settable means for controlling axial displacement of the piston in the cylinder towards the said outlet, so that when the said foodstuff inlet is connected to a supply of food under pressure and the inlet valve is opened, the food is admitted to the cylinder to push it back until it reaches its fully withdrawn position causing the inlet valve to close, sterilized medium under pressure then being admitted to the rear of the piston to push the piston back along the cylinder until it reaches a limit position determined by pre-settable means whereby an exact volume of food displaced by movement of the piston is dispensed through the outlet.

In preferred metering devices of the invention, the piston has a shaft extending rearwardly therefrom, the pre-settable means comprising means on the shaft which cooperate with adjustable limit stops operably associated therewith to control the length of the stroke of the piston.

Preferably the piston includes an annular groove around the periphery thereof to provide an edge seal between the piston and cylinder wall, said groove having a supply duct connected thereto by means of which a sterilizing medium such as steam can be supplied to the annular groove. Conveniently, an exhaust duct venting to the atmosphere is also connected to the annular groove.

In a preferred embodiment, the shaft is a hollow tube through which, in use, sterilizing medium is fed to the supply duct and hence to the annular groove in the piston. Preferably the piston has a central portion intermediate its ends made of a plastics material in which are the annular duct and the supply and exhaust ducts.

Preferably the cylinder has an end wall with a recess adjacent the said inlet and outlet into which an end portion of the piston is located when the piston has travelled along the whole length of the cylinder, towards said end wall, the recess defining a space between the front face of the piston and the surface of the recess. The purpose of this recess is to ensure that any particulate material left in the cylinder at the end of a stroke of the piston is not compressed and therefore damaged by the piston on its next stroke.

A preferred process, apparatus and metering device of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of food processing apparatus incorporating the present invention;

Figure 2 is a schematic view of a part of the apparatus shown in Figure 1; and

Figure 3 is a cross section through the metering device of the apparatus shown in Figures 1 and 2.

Referring to Figure 1, a pre-mix container 1 receives recipe ingredients for the food which is to be cooked and eventually packaged. Depending on the final food product, the ingredients may be completely cooked ready for packaging or alternatively they may be partially cooked for packaging in a partially-cooked condition, for example where they are to be supplied to a manufacturer for completion of a cooking cycle. For instance, steak and kidney can be partially cooked and packed in a pre-sterilized pack ready for supply to a manufacturer of steak and kidney pies, the pie manufacturer then placing cooked meat in a pastry envelope which is then cooked. This later cooking cycle will complete the cooking of the partially cooked steak and kidney so that when the pie is delivered to the customer, the contents of the pastry envelope will also have been fully cooked.

After completion of the cooking cycle, or at least the desired degree of cooking of the ingredients in the pre-mix container 1, the ingredients are passed through a duct 2 into a pump 3 which is preferably a "MARLEN" pump of known type. The pump 3 forces the ingredients to be at least partially cooked upwardly through an ohmic column 4 where heat is generated internally in the ingredients by the passage of an electric current through them using electrodes 4a, a sterilization temperature being achieved in a very short time. The temperature achieved and heating times used will be varied according to the food being processed. As solids are heated as quickly as liquids, this method is extremely useful for processing foods containing particulate materials, such as steak and kidney, curry, spaghetti bolognaise, chilli, etc. With prior art methods, it has been very difficult to heat foods containing particulate materials because the liquid content of the foods tends to heat up more quickly than do the particulate materials in the foods. Heating the whole of the food to a temperature which would kill the relevant micro-organisms has therefore been uncertain. By way of example, if the ohmic column 4 is approximately six metres high and has four electrodes 4a spaced along its length, a pre-cooked food can enter the bottom of the column 4 at a temperature of approximately 70°C and, by the time it leaves the top of the column, the temperature of the food can be increased to 142°C. Foods are preferably heated in the column 4 at a rate of approximately 1°C rise per second, but this will usually be varied according to the food being processed. Accordingly, it takes approximately seventy seconds for the food to be sterilized completely by the time it leaves the top of the column 4 in the illustrated example. Food processed using apparatus in accordance with the present invention will always include a liquid as a carrier for particulates therein. The liquid can take the form of gravy or a sauce. As the food has to be heated to about 142°C to ensure it is sterilized completely, it will be appreciated that water in the food would normally boil off by the time it leaves the top of the column 4. The apparatus is, therefore, pressurized to a pressure of 60 p.s.i. (four bar) to lower the effective boiling point of water in the food, and thereby avoid this evaporation.

In the illustrated example, the food leaving the top of the column 4 passes into a holding tube 5 where it is stabilized for a period of approximately sixty seconds. During this stabilization period, the temperature of the food drops to about 140°C. The food is then passed through a multiple cascade cooler 6 over a period of 15-20 minutes where the temperature of the food is reduced to 25°C. On leaving the cooler 6, the food enters a storage tank 7 blanketed with an inert gas (preferably nitrogen) at a pressure of four bar (60 p.s.i. ) .

The storage tank 7 has an outlet duct 8 closed by a first valve 9. The outlet duct 8 supplies sterilized food from the tank 7 to a metering device 10 having an outlet 11 leading to a fill head 13 by means of which the sterilized food is put into a pre-sterilized package (not shown). The output from the fill head 13 is controlled by a second valve 12.

The process effected in the apparatus illustrated in Figure 1 operates on a continuous basis, sterilized food being dispensed continuously from the fill head 13 into pre-sterilized packs (not shown) using the metering device 10 to be described in more detail hereafter. A major advantage of the hereinbefore described apparatus in accordance with the present invention is that only one storage tank 7 is required rather than the two tanks of prior art processes. Also, only a relatively small quantity of sterilized food needs to be stored in the tank 7 because the metering device 10 works in conjunction with the fill head 13 so the food being processed is not held in the storage tank 7 long enough to allow it to separate out into separate stratified layers. Another advantage is that food can be dispensed directly from the storage tank 7, even though it is maintained at a pressure of four bar, as a result of the metering device 10.

Figure 2 illustrates in more detail a part of the apparatus shown in Figure 1. The storage tank 7 in which sterilized food is held under pressure has an outlet 8 connected to an inlet 15 of the metering device 10. The inlet 15 is closed by the valve 9. The metering device 10 has an outlet 16 connected to a duct 11 leading to the fill head 13. The valve 12 in the duct 11 controls the output of food from the fill head 13.

As shown in Figure 3, the metering device 10 includes a piston 14 reciprocable within a cylinder. A sterilized medium, preferably steam, is supplied to the rear of the piston 14 (from above as shown in the drawing) at a pressure , of 3.5 bar through a valve-controlled inlet 17, and it is exhausted via valve-controlled outlet 18. A tube 19 projects upwardly from the rear of the piston 14 and it has a trigger 36 mounted thereon which cooperates with limit switches 20 and 21. The operation of the valves 9, 12, 17 and 18, and of the limit switches 20, 21 and 36, is controlled by central control means 22, preferably a computer. The pressures mentioned above are preferred. Other pressures may be used, if desired.

The operating cycle of the apparatus shown in Figure 2 will be described in more detail following a description of the metering device 10 with reference to Figure 3.

In Figure 3, the metering device 10 includes a piston and cylinder arrangement. The valve 9 is in the inlet 15 to the cylinder, and the outlet 16 from the cylinder is connected to the duct 11 leading to the fill head 13 (not shown in Figure 3) . The inlet 15 and the outlet 16 open into a recess 52 in the lower end wall of the cylinder, the recess 52 having an annular bevelled edge 51 which cooperates with a corresponding bevelled edge 50 around the bottom of the piston 14. The vertical axial distance between the top and bottom of the bevelled edge 50 of the piston 14 is less than the axial depth of the recess 52 so a small gap remains between the bottom of the piston 14 and the bottom of the recess 52 when the bottom of the piston 14 fits within the recess 52. In a preferred embodiment, this gap will be approximately one inch, the purpose thereof being to avoid damaging food particles left in the cylinder on completion of an operating cycle in which food would otherwise be crushed and damaged if it were not for this gap.

The piston 14 is made up from three separate parts held together by bolts 48. Upper and lower parts 41, 40 are of metal whereas a central portion 42 is preferably made of a plastics material. The piston 14 could be made completely of metal, but this would substantially increase its weight and its cost of manufacture.

The central portion 42 of the piston 14 has a duct 47 extending radially outwardly from its center to communicate with an annular groove 46 around its periphery. The central duct 47 communicates via a tube 33 with a steam supply, and it will be seen that when steam is fed through the tube 33, a steam barrier will be provided at the edge of the piston between its front and rear faces. The piston 14 additionally includes known sealing O-rings 44 and 45. The ends of the cylinder are closed by end caps 39a and 39b including respective O-ring seals 43a and 43b.

The tube 19 connected to the rear of the piston 14 extends outwardly from the cylinder through the end cap 39b. The end of the tube 19 remote from piston 14 is closed by a plug 34. The smaller diameter hollow tube 33 passes through the plug 34 and is sealed with respect thereto by known sealing rings 37. This hollow tube 33 is connected to the duct 47 leading to the annular groove 46 which provides the steam barrier, and steam is provided to the annular duct 46 via this tube 33. Steam exhausts from the annular groove 46 via an exhaust duct 53 communicating with the interior of the hollow tube 19 and venting to atmosphere via a duct 55 and a steam outlet 35. O-ring seals 49 in the end cap 39b make a fluid tight seal with the exterior of the hollow tube 19 which is movable relative to the end cap 39b on movement of the piston 14.

Pre-settable control means mounted on the cap 39b consisting of a pillar 30 connected by a bridge 31 to a rod 32. Pillar 30 and rod 32 are fixably mounted in the end cap 39b. Limit switches 20, 21 are slidably mounted on the rod 32. A trigger 36 is attached to the plug 34 closing the end of the hollow tube 19 by screws in known manner. The limit switch 20 senses the fully raised or withdrawn positions of the piston 14, and the lower limit switch 21 is adjustable and can be set to a position corresponding to the volume of food which is to be dispensed on the downward stroke of the piston 14.

Operation of the illustrated apparatus is as follows:

(1) at the start of a cycle, the piston 14 is located at its lowest position dictated by the limit switch 21; the product inlet valve 9 is closed; sterilized medium is supplied via inlet 17 to the rear of the piston 14, until a pressure of 3.5 bar is reach; and the outlet valve 18 is then closed;

(2) the inlet valve 9 is opened and food at a pressure of 4 bar forces the piston 14 to retract from the position shown by broken lines in Figure 3 against the 3.5 bar pressure at the rear of the piston 14, this pressure being slowly bled off to atmosphere using the restrictor valve 18 which is now open - as valve 17 is now closed, the piston 14 withdraws slowly because a pressure differential of only 0.5 bar is applied to it rather than the 4 bar applied previously;

(3) when the piston 14 reaches its fully withdrawn or raised position, the trigger 36 contacts the limit switch 20 to close the inlet valve 9, open the inlet valve 17 and close the exhaust valve 18 so that the sterilized medium can again be applied to the rear of the piston 14 - once this pressure has been reached, the valve 12 associated with the fill head 13 is opened so the piston 14 moves downwardly to expel food from the cylinder; and

(4) when the trigger 36 reaches the limit switch 21, the piston 14 will have reached the limit of its downward stroke required to dispense a pre-set volume of food, so the inlet valve 9, the outlet valve 12, and the inlet 17 are all closed and the restrictor valve 18 is opened before the cycle is repeated. The sterilized medium supplied to the rear of the piston 14 through the inlet 17 is preferably steam, although some other sterile fluid such as air or nitrogen could be used. Steam is preferred because it cannot contaminate food in the cylinder. Also, supplying steam to the annular groove 46 has the same effect, so a very sterile environment can be provided. It should be noted that with the illustrated apparatus, the piston 14 is moved on its upward stroke as a result of the pressure of the food supplied to the cylinder, and it is returned by supplying a sterilized medium to the rear of the piston 14 through the valve controlled inlet 17.

It will be appreciated from the foregoing description that processed food can be very accurately metered into pre-sterilized packs at a substantially constant density and pressure, so the process described provides a considerable improvement over prior art processes.

Claims

1. Apparatus for metering a predetermined quantity of aseptic food containing particulate matter into a pre-sterilized package, the apparatus comprising a pressurizable storage tank for the aseptic food to be dispensed and packaged, said tank being connected to a valve-controlled inlet of a metering device, the metering device having an outlet connected to a fill head, the output of the outlet being controlled by a valve, the metering device further comprising a cylinder and a cooperating piston so that food under pressure from the storage tank is forced into the cylinder on opening the inlet valve thereto to cause the piston to retract, the metering device also including means for supplying a sterilized fluid to the rear of the piston and maintaining said fluid at a pressure slightly less than that in the storage tank whereby on opening the said outlet connected to the fill head and closing the inlet valve to the cylinder, the piston is moved along the cylinder to expel food therefrom, the length of the expelling stroke of the piston being controlled by pre-settable control means operably associated with the means for supplying the sterilized fluid to the rear of the piston.

2. Apparatus as claimed in claim 1, wherein the contents of the storage tank are maintained at a pressure of substantially four bar, and the sterilized fluid is supplied to the rear of the piston at a pressure of approximately 3.5 bar.

3. Apparatus as claimed in claim 1 or claim 2, wherein the piston is fully retractable when the inlet valve to the metering device is opened.

4. Apparatus as claimed in any of the preceding claims, wherein the piston has a shaft extending rearwardly therefrom, the pre-settable control means comprising adjustable limit switches operable to sense the position of the shaft on movement of the piston during its return stroke whereby the supply of fluid under pressure to the rear of the piston is cut off when the shaft reaches a pre-set position.

5. Apparatus as claimed in claim 4, having a trigger mounted on the shaft to cooperate with the adjustable limit switches, the switches being disposed alongside the shaft, and the position of said switches being adjustable to vary the length of the operating stroke of the piston.

6. Apparatus as claimed in any of the preceding claims, wherein the supply of sterilized fluid to the rear of the piston is controlled by a valve, operation of this valve, the fill head outlet valve and the metering device inlet valve being controlled by central control means.

7. Apparatus as claimed in any of the preceding claims, wherein the piston has an annular groove around its periphery, said groove being connected to a supply of steam so that, in use, a steam barrier or seal is provided between the piston and cylinder wall when steam is supplied to said groove.

8. A method of metering a predetermined quantity of aseptic food containing particulate material from a storage tank under pressure to a pre-sterilized package, the method comprising the steps of opening a first valve to admit food from the storage tank into a metering device comprising a piston reciprocable in a cylinder whereby the piston is forced back by the food under pressure, a sterilized medium being supplied to the rear of the piston at a pressure less than that in the storage tank; subsequently closing a valve to cut off the further supply of food to the cylinder; and then opening a second valve downstream of the metering device whereby the piston is forced back under the pressure of the sterilized medium to expel food from the cylinder, the length of the return stroke of the piston being controlled by pre-settable control means whereby a predetermined volume of food is dispensed from the metering device to the pre-sterilized package.

9. A metering device for dispensing a predetermined volume of a foodstuff containing particulate matter, the foodstuff being supplied under pressure to the device in a sterilized condition, the device comprising a piston reciprocable in a cylinder, a foodstuff inlet to the cylinder controlled by a valve, a foodstuff outlet from the cylinder, means for supplying a sterilized medium under pressure to the rear of the piston, the supply of said sterilized medium being controlled by a valve and pre-settable means for controlling axial displacement of the piston in the cylinder towards the said outlet so that when the said foodstuff inlet is connected to a supply of food under pressure and the inlet valve is opened, the food is admitted to the cylinder to push it back until it reaches its fully withdrawn position causing the inlet valve to close, sterilized medium under pressure then being admitted to the rear of the piston to push the piston back along the cylinder until it reaches a limit position determined by pre-settable means whereby an exact volume of food displaced by movement of the piston is dispensed through the outlet.

10. A metering device according to claim 9, wherein the piston has a shaft extending rearwardly therefrom, the pre-settable means comprising means on the shaft which cooperate with adjustable limit stops operably associated therewith to control the length of the stroke of the piston.

11. A metering device as claimed in claim 9 or claim 10, wherein the piston includes an annular groove around the periphery thereof to provide an edge seal between the piston and cylinder wall, said groove having a supply duct connected thereto for the supply of sterilizing medium.

12. A metering device as claimed in claim 11, having an exhaust duct connected to the annular groove for venting the groove to the atmosphere.

13. A metering device as claimed in claim 11 or claim 12, wherein the shaft is a hollow tube through which, in use, sterilizing medium is fed to the supply duct and hence to the annular groove in the piston-

14. A metering device as claimed in claim 12 or claim 13, wherein the piston has a portion intermediate its ends made of a plastics material in which are the annular duct and the supply and exhaust ducts.

15. A metering device as claimed in any of claims 9 to 13, wherein the cylinder has an end wall with a recess adjacent the said inlet and outlet into which an end portion of the piston is located when the piston has travelled along the whole length of the cylinder towards said end wall, the recess defining a space between the front face of the piston and the surface of the recess.