GB2046073A - Pasteurisation apparatus - Google Patents

Abstract

Apparatus for the pasteurization of milk by the batch method includes a process tank for the milk having a double wall defining a peripherally continual cavity; a self-standing storage unit which includes an upright heated water tank and an upright chilled water tank containing evaporator coils of a refrigeration system; two pipelines interconnecting the process tank cavity with the storage unit for supply to and return from the process tank cavity of heating and cooling water; an electrical circulating pump; a refrigeration compressor; and a system of interconnecting pipelines and solenoid-operated valves to control the sequence and direction of flow of water to and from the process tank cavity, and first and second means to connect the apparatus to water and electricity supplies, respectively.

Description

SPECIFICATION Pastomilk -- PS 225 Model "A" General Characteristics The PS 225 model "A" is mainly conceived for those users who have only singlephase power supply and a limited power availability.

The pasteurisation of the milk must be carried out just after milking, therefore in the morning and in the evening, with intervals of several hours between the two operations. We overcame the shortage of power by storing heat and cold through two water tanks in which the heat energy necessary to the pasteurisation is stored during the period elapsing between the two subsequent pasteurisations.

Thanks to the heat energy, we obtained a sensible reduction of the installed power and consequently the possibility of using a singlephase power.

We therefore recommend the use of model "A" wherever there is shortage of power supply, such as the case of singlephase, but also in case of threephases, whenever all available power is almost saturated by users.

Putting into operation The pasteurisation of the milk is obtained by heating, pre-cooling and cooling the milk by forced circulation of water through a pump, in the liners of the pasteurisation tank. This cycle, fully recorded, takes place automatically by pushing the start button.

The heating water is taken from the hot tank The pre-cooling water is taken from the network water The cooling water is taken from the cold tank As soon as the milk reaches the established temperature, the thermostat on the heating circuit stops the pump and relative circulation of warm water.

Then the timer starts functioning. As a matter of fact for the established period, it will not allow the starting of the pre-cooling cycle. In the meantime, should the temperature of the milk decrease, the thermostat on the heating circuit will re-set the forced circulation of warm water and re-establish the temperature.

When fixed time is over, the timer will automatically start the pre-cooling cycle.

When the temperature of the milk will be decreased to the value established on the second thermostat, the cooling phase will start.

As soon as the temperature of the milk decreases to the established value, the system will keep automatically the storage temperature through a third thermostat.

The Pastomilk PS 225 Batch Pasteuriser The Pastomilk PS 225 has been developed for the pasteurisation of milk by the batch method in installations where only a single phase supply of electricity is available. The pasteuriser was supplied by the manufacturer, Cattabriga S.p.A. of Bologne, Italy, through their agents in the United Kingdom, Messrs. Cof Nardini Refrigeration Limited of Largs, Ayrshire. It was provided to permit a critical evaluation to be made to determine its suitability for the production of pasteurised milk which conforms to the statutory regulations operative in Scotland at the present time.

1. GENERAL DESCRIPTION The pasteuriser consisted of separate components -- a self standing storage unit and the jacketed process tank. The storage unit, which was 2000 mm x 1000 mm x 2115 mm high (78 in x 39 in x 83 in high) comprised: (a) the chilled water tank of approximately 1 200 (264 gallons) capacity contained the evaporator coils of the refrigeration system, and was fitted with a centrally mounted agitator; (b) the heated tank contained 600 (132 gallons) of water which was heated by one 4 kW electric immersion heater. A spare immersion heater was also fitted in the hot water tank, but was not connected. This was fitted to act as a spare, or it could be wired up to expedite the rate of heating.

During the trials only one immersion heater was used.

(c) an electric circulating pump of 0.4 kW rating, a refrigerator compressor of 1.1 kW rating and the system of interconnecting pipeline and solenoid operated valves which controlled the sequence and direction of liquid flow to and from the process tank.

The jacketed process tank was separate from the storage unit to which it was connected by two rubber hoses -- inlet and return line of the heating and cooling media - and the electric power and control cable. To the 227 (50 gall) stainless steel tank which was contained in a cabinet 865 mm x 865 mm x 1060 mm high (34 in x 34 in x 42 in high), was fitted a control panel which carried the recording thermograph, the two switches which initiated the process, the switch for the agitator of the process tank and six lamps which indicated the stage of the process. The process tank was fitted with a stainless steel lid through which was fitted a twin two bladed vertical agitator which was mounted off centre and driven by a 0.12 kW motor rotating at 1 6 r.p.m.The outlet of the tank was closed by a 12 in (38 mm) butterfly type valve. Since the rubber hoses and the electric cable connecting the service unit with the process tank were approximately 9 m (29 ft.) long, the process tank could be contained within the dairy whilst the service unit could be positioned outside the building. This would permit the process tank to be placed in the most convenient position to feed the milk bottling or packaging system. Were it to be placed at a higher level the milk could then be discharged by gravity.

2. SERVICE REQUIREMENTS The plant has been designed to require only a single phase electricity supply with which the necessary heating and cooling of the milk in the process tank is carried out. The maximum electrical loading for the equipment is 240 v 25 amp. In addition to the electricity, a water supply is necessary, not only for the cooling of the refrigeration condensor, but also as the pre-cooling treatment of the heated, held, milk. To effect this cooling satisfactorily, mains water of a minimum pressure is essential. The water is controlled at its inlet to the machine by a pressure regulator being maintained between 1 and 1.5 kg/cm2 (14.2-21.3 p.s.i.), and it is imperative that this pressure is measured when the plant is not operating.

3. OPERATION OF THE PLANT Since the heating, and also the cooling of the milk is effected by the circulation from the storage tanks contained within the storage unit, it is necessary that the unit be operated for sufficient time to ensure that the chilled water is at 1 OC (340F) and the temperature of the hot water is at 90"C (194OF).

To achieve this, the main switch of the control box of the storage unit is left switched on at all times.

When the two tanks are at the desired temperature, a light, labelled 'rating', is illuminated on the control panel which indicates that the system is then ready for processing to begin.

Milk is then added to the tank. Whilst the nominal capacity of the tank is 227 (50 gallons) it could contain 290 (64 gallons). The pasteurisation process is commenced by switching on the tank agitator, (selector switch 1) rotary switch 2 and then the push button 3. The heating of the milk is then effected by the hot water which is withdrawn from the tank by the centrifugal pump, forced through the tank jacket and then returned to the hot water tank. The direction of flow is controlled by the operation of solenoid valves D and F (diagram 1). This stage in the process is indicated by the lighting up of the lamp labelled 'heating'.

When the milk reaches the required temperature of 62.5 OC (1 450F) the pump is automatically switched off and the temperature maintained between 630C and 650C (145-1490F) during the 30 minute holding period, and this stage is shown by the 'holding' lamp being energised.

Preliminary cooling, at the end of the holding period, is by mains water and this is commenced immediately after the holding period. Water is fed from the mains to the pump from where it is forced through the jacket of the process tank, being discharged to waste by the operation of the solenoid valves C and G (diagram 1). This is indicated on the panel by the light labelled 'pre-cooling'. The cooling by mains water continues until the temperature of the milk is lowered to 280C (820F). This temperature is established by the thermostat which is fitted within the jacket of the processing tank.When the milk reaches this temperature the supply of mains water to the pump is stopped and by the operation of solenoid valves E and H (diagram 1), chilled water is withdrawn from the storage tank within the storage unit, fed to the centrifugal pump and forced through the jacket and back again to the chilled water storage tank. The chilled water continues to be circulated until the milk in the process tank is cooled to a temperature of 5--7 OC (41-450F). When this temperature is reached the pump is switched off and the warning light 'ageing' appears. The milk is automatically controlled at this temperature with the agitator operating until the system is switched off at the control panel.

4. ASSESSMENT OF HEAT TREATMENT Using the procedure described above, the plant was operated on twenty three different occasions using either milk or water. The raw milk was from a normal commercial bulk milk supply, delivered from a road tanker from farms. The hygienic quality varied widely, and is shown in the results. A sample of the raw milk was withdrawn immediately before the pasteurisation was commenced. The pasteurised milk was sampled by withdrawing a quantity from the surface of the milk in the tank with a sterile dipper, and on two occasions was also sampled from the tank outlet.

These samples were tested as below, and, where appropriate, in accordance with Milk (Special Designations) (Scotland) Order 1 965.

4.1 Total Plate Count. Total count was determined on dilutions of 1/10, 1/100, and 1/000 ml at 300C for 3 days using plate count agar.

4.2 Thermoduric Organisms. Total count after laboratory pasteurisation (630C for 30 minutes) using milk count agar.

4.3 Coliform Organisms. Presumptive test on 1/10, 1/100 and 1/1000 ml; 4.4 Phosphatase Test. The method of Aschaffenburg and Mullen was used.

4.5 Creamline. The effect of the treatment on the creaming propensities of the milk was also determined. Two hundred ml of untreated milk was held in a measuring cylinder at ambient temperature and the cream volume developed after 24 h was measured and compared with that of a similar volume of the same milk after pasteurisation held under similar conditions.

4.6 Effectiveness of Cleaning and Sterilisation Routines. Plant hygiene was assessed by swabbing selected parts of the plant and determining the total colony count using plate count agar at 300C for 3 days.

5. TEMPERATURE AND TIME OF PROCESSING The temperature of pasteurising is determined by the setting of the controls which are incorporated in the electrical equipment of the storage unit, except for the thermostat controlling the temperature to which pre-cooling is continued, which is fitted inside the jacket of the process tank. All the controls which had been previously established by the manufacturer, did not require any adjustment from batch to batch, and were not altered during the course of the trials.

5.1 Temperature -- Recording Equipment. The temperature recorder is manufactured by Spriano S.p.A., of Milan. The electrically rotated 24 hour chart has a range of 0--1000C in graduations of 20C.

The temperature sensing bulb is not immersed in the milk in the tank but is fitted within the circulating medium in the tank jacket and appears to measure the temperature of the medium returning to the storage unit. The accuracy of the temperature recording instrument was compared with that of the milk in the tank either by a thermocouple or by a mercury in glass NPL tested thermometer. It was found that there was close agreement between the temperatures shown by the three systems and the maximum variation between the recording thermometer and others was found to be less than 1 OC. A more exact comparison was difficult to measure due to the distance between graduations, particularly at the lower end of the range where they were only 1.5 mm apart.

5.2 Temperature -- Speed ofResponse. In the comparison of temperature it was noted that there was a time lag between a change of temperature shown on the recorder and that by a hand held thermometer in the milk. The lag was however uniform over the whole processing range and would not affect either the efficiency of the process nor the accuracy of the temperature recording.

5.3 Temperature -Agreement with Established Settings. The temperature at which the different stages of the process control occurred agreed with those stated by the manufacturer -- heating to 650C, pre-cooling to 280C and final cooling to 70C. The only variations occurred when the contents of the tank was 30 gallons (136 litres) or less, when the temperature rose during the holding period (See Section 9.2).

5.4 Holding. The time of holding was checked during each processing operation and was found to be 30 minutes irrespective of the volume within the processing tank.

6. CLEANING AND STERILISING 6.1 Cleaning. No difficulty was experienced in cleaning the plant at the end of each operation. A proprietary general purpose hand detergent was used at a recommended concentration of 0.5%. The residual soil was principally of a fatty nature so that a detergent with good emulsifying characteristics would be required, although the detergent used was not selected with marked emulsifying powers. The underside of the tank lid and the twin bladed paddles are two areas which require particular attention in the cleaning. The design of the plant considerably facilitates the cleaning. The lid is hinged in the middle, which permits access to the tank contents.In addition the whole lid is hinged which allows the whole of the underside to be exposed and this action also releases the paddle which is retained between a stud on the base of the tank and a slip ring on the underside of the tank lid.

It is necessary that the straight through valve be disassembled to permit satisfactory cleaning.

6.2 Sterilisation. The plant was sterilised by a solution of sodium hypochlorite containing 100 parts per million of available chlorine. This solution was applied immediately before the tank was filled with milk and all milk contacting surfaces were exposed to the solution for at least 4 minutes, when the tank was drained.

7. ELECTRICAL AND WATER REQUIREMENTS The electricity supply was through a meter which permitted the consumption to be measured.

Similarly, the water supply was metered in order to determine the water consumption.

8. RESULTS 8.1 Bacteriological analysis of Milks.

Total count Presumptive Thermoduric (per ml) coliforms count (per ml.) 72hat300C 72 hat3O0C 8.1.1 Untreated milk mean 180,000 +10-3 18,000 range (60,000-) + 10-3 15,000-33,000 (-268,000) 8.1.2 Pasteurised milk.

mean 21,000 absent range 14,000-35,000 absent 8.2 Plant Hygiene Three areas of the plant were examined for the efficiency of cleaning and sterilisation approximately one square foot of the internal surface of the process tank was swabbed; the surface of the agitator, particular attention being paid to the underside of the paddles, and the junction of the shaft with the base of the tank; the valve which was disassembled and the internal port swabbed.

The results obtained from tests taken on the trial runs when plant hygiene was assessed are given below: Total colony count Coliform organisms (in 1 ml of swab rinse) Internal tank surface (per sq. ft.) 425 absent Agitator (count per ml of swab rinse) 200 absent Valve (count per ml of swab rinse) 100 absent 8.3 Phosphatase Test. During each experimental run a sample was submitted for the phosphatase test. Ali samples passed the test.

8.4 Creamline. The effect of heat treatment on creamline development was determined by measuring the difference in volume of the visible cream layer formed on untreated and pasteurised samples of the same milk held for 24 hours at ambient temperatures. The following results were recorded: Percentage reduction in cream layer 0 1 2 3 4 5 6 Number of samples 6 15 2 1 0 0 0 RANGE 0--3% 8.5 Electricity Consumption. The electrical consumption was not only required during the batch processing but also for the recuperation of the chilled water and hot water which is retained in the storage unit. The total consumption was therefore determined by recording the reading when the 'rating' light operated before the process had been compieted. It was found that the time for the recuperation of the system was approximately three hours, after which it was possible to process another batch.

The consumption of electricity for one batch, as measured above, averaged 1 7.5 kW during the trials.

8.6 Water Consumption. The water was needed to cool the refrigerator compressor and also for the pre-cooling part of the process. This was metered, in a similar manner to that of the electricity, vide supra, and was found to average 2.7 m3 (330 gallons).

9. TEMPERATURE AND VOLUME OF MILK RELATED TO TIME OF PROCESSING Trials were also carried out to determine the effect, if any, of smaller volumes of milk and also of higher initial temperature, on the time of heating, and cooling and also on the temperature of holding.

The results are tabulated below: Relationship between milk volume, initial temperature of milk, rate of heating and cooling and temperature of holding.

A B C D E Initial temperature of milk (OC) 8 8 7 7 38 Volume of milk in tank in gallons 50 60 30 20 50 Temperature of hot water (OC) 90 90 90 90 90 Time of heating in minutes 30 40 30 1 6 1 5 Highest temperature during holding OC 63 63 65 67 63 Time of cooling (minutes) 80 90 60 15 80 Total operating time in minutes 140 160 120 60 125 The results are shown on the attached graphs.

10. DISCUSSION OF RESULTS AND OBSERVATIONS 10.1 Milk Quality. The quality of pasteurised milk produced by the Pastomilk PS225, operated as described, conformed in every respect to all statutory and commercial requirements. The quality of the untreated milk was extremely variable but milk of a satisfactory bacteriological quality was consistently obtained, even when milk of a poor hygienic standard was processed.

To determine the bactericidal effectiveness of the system, high count milk was produced by adding a small quantity - 5 (0.9 gallon) of aged milk to the fresh untreated milk contained in the process tank. The efficiency of the process was clearly demonstrated by the results of pasteurising such poor quality milk which was similar to the same milk when laboratory pasteurised.

With untreated milk of average quality no difficulty would be experienced in producing a consistently satisfactory quality of pasteurised milk. No difficulty was experienced in satisfying the phosphatase test, and ail samples passed the test.

The pasteurised milk suffered the least damage to creamline of any system of pasteurisation which has been examined at the Dairy Technology Department of the West of Scotland College of Agriculture. 87.5% of the samples examined had a creamline reduction of 1% or less when compared with the same milk before pasteurising.

10.2 Temperature and Time ofProcessing. The temperature recording equipment was shown to be accurate, sensitive and quite satisfactory. A lag in the response of the recording instrument is discussed in Section 5.2.

The process temperature was controlled by that of the recirculated hot water which was thermostatically controlled at 900C (194OF). This proved to be satisfactory, even when the process tank contained more than 227 (50 gallons). However when smaller quantities of milk were processed trial runs were carried out with 136 and 91 1 (30 and 20 gallons respectively) -- it was found that, although the circulation of the hot water ceased when the pump was switched off when the milk reached 630C (1450F), the temperature of the milk continued to rise during the holding period. This would be due to the residual heat capacity of the quiescent hot water in the jacket of the tank.When the tank contained 50 gallons or more, this heat input was adequate to maintain the holding temperature at the desired level. When the tank contained 30 gallons the highest temperature reached during the holding period was 650C (1 490F) and for 20 gallons the temperature reached was 67 OC (1 520F).

The effect was also investigated when the initial temperature of the milk corresponded to that of uncooled untreated milk, as would be delivered direct from a milking installation on a dairy farm. The initial temperature of the milk was 380C (1 000F) and it was noted that this reduced the 'come-up' time by half. Other than this, there was no change in operating times and temperatures.

10.3 Suggested Modifications. In the course of the trials it was appreciated that two minor modifications, whilst not improving the performance of the plant, which was shown to be satisfactory, could facilitate its operation and maintenance.

(a) The type of valve would not permit a pipeline to be attached to convey the milk to either a storage tank or the packaging or bottling plant. It is suggested that a valve with a threaded outlet would allow this.

(b) The maintenance of the refrigeration equipment would be eased were the controls and valves fitted towards the access hatch. Difficulty was experienced in adjusting a water valve which had been fitted towards the back of the control area when this aspect became apparent.

11. SPECIFIC APPLICATION OF EQUIPMENT This system presents a unique facility in that only a single phase electricity supply is required to permit the production of pasteurised milk of a satisfactory quality with a high degree of efficiency with the operation of the plant being completely automatic. In a farm situation it would be practicable to process milk direct from the milking installation, with no preliminary cooling. It would, however, be necessary to ensure that the chemical quality of the milk is satisfactory by mixing the morning and evening production. The system could be started before the tank is full, provided that no milk was added once the holding period was started, and this would shorten the processing time.It is preferable that batches not less than 130 (29 galls) be processed, or there may be some damage to the creamline, as a result of the elevated temperature of holding.

12. FINAL CONCLUSION The Pastomilk PS220 system provides a system of batch pasteurisation which is compact, of fully automatic operation, and which economically produces a pasteurised milk of a high quality and with no damage to the creamline. The controls are simple and the processing techniques would present no difficulty to an operator, and cleaning is easily effected using a hand detergent. Such an installation would be most suitable for the processing of quantities of milk up to approximately 680 1(1 50 gallons).

The system can also be supplied with a three phase electricity system which would permit a more compact unit, and possibly a shorter recuperation period.

CLAIMS (Filed 12 Dec 1978) 1. Apparatus for the pasteurizing of milk by the batch method and including separate tanks for the storage of water with continual heating and chilling, respectively.

2. Apparatus for the pasteurization of milk by the batch method, said apparatus comprising a process tank for the milk having a double wall defining a peripherally continual cavity; a self-standing storage unit which includes an upright heated water tank and an upright chilled water tank containing evaporator coils of a refrigeration system; two pipelines interconnecting the process tank cavity with the storage unit for supply to and return from the process tank cavity of heating and cooling water; an electrical circulating pump; a rerigeration compressor; and a system of interconnecting pipelines and solenoid-operated valves to control the sequence and direction of flow of water to and from the process tank cavity, and first and second means to connect the apparatus to water and electricity supplies, respectively.

3. Apparatus according to Claim 2, wherein the hot-water tank is fitted with an electric immersion heater.

4. Apparatus according to Claim 2, wherein the hot-water tank is supplied from a hot-water boiler.

5. Apparatus according to Claim 2, wherein the chilled-water tank is fitted with an axiallymounted agitator.

6. Apparatus according to any one of the preceding claims, wherein the process tank for the milk is fitted with an agitator which is mounted off centre.

7. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 1 of the accompanying drawings.

8. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 2 of the accompanying drawings.

9. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 3 of the accompanying drawings.

1 0. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 4 of the accompanying drawings.

11. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 5 of the accompanying drawings.

1 2. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 6 of the accompanying drawings.

1 3. Apparatus for the pasteurization of milk by the batch method and with the set-up hereinbefore described with reference to Fig. 7 of the accompanying drawings.

New claims or amendments to claims filed on 27 Nov 1 979.

Superseded claims 1 to 13.

New or amended claims: 1 to 12.

Claims (12)

1. Apparatus for the pasteurization of milk by the batch method, said apparatus comprising a process tank for the milk having a double wall defining a peripherally continual cavity; a self-standing storage unit which includes an upright heated water tank and an upright chilled water tank containing evaporator coils of a refrigeration system; two pipelines interconnecting the process tank cavity with the storage unit for supply to and return from the process tank cavity of heating and cooling water; an electrical circulating pump; a refrigeration compressor; and a system of interconnecting pipelines and solenoid-operated valves to control the sequence and direction of flow of water to and from the process tank cavity, and first and second means to connect the apparatus to water and electricity supplies, respectively.

2. Apparatus according to Claim 1 , wherein the hot-water tank is fitted with an electric immersion heater.

3. Apparatus according to Claim 1, wherein the hot-water tank is supplied from a hot-water boiler.

4. Apparatus according to Claim 1, wherein the chilled-water tank is fitted with an axiallymounted agitator.

5. Apparatus according to any one of the preceding claims, wherein the process tank for the milk is fitted with an agitator which is mounted off centre.

6. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1, and with the set-up hereinbefore described with reference to Fig. 1 of the accompanying drawings.

7. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1 and with the set-up hereinbefore described with reference to Fig. 2 of the accompanying drawings.

8. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1 and with the set-up hereinbefore described with reference to Fig. 3 of the accompanying drawings.

9. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1 and with the set-up hereinbefore described with reference to Fig. 4 of the accompanying drawings.

10. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1 and with the set-up hereinbefore described with reference to Fig. 5 of the accompanying drawings.

11. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1 and with the set-up hereinbefore described with reference to Fig. 6 of the accompanying drawings.

12. Apparatus for the pasteurization of milk by the batch method as claimed in claim 1 and with the set-up hereinbefore described with reference to Fig. 7 of the accompanying drawings.