TECHNICAL NOTE

DEVELOPMENT OF A MOBILE JUICE AND WINE PASTEURIZER

E. M. Lauro and T. Fuleki

Horticultural Research Institute of Ontario, Ministry of Agriculture and Food,Vineland Station, Ontario LOR 2E0

Received 13 February 1985, accepted 8 April 1986

Lauro, E. M. and T. Fuleki. 1987. Developmentof a mobilejuice and wine pasteurizer. Can. Agric. Eng. 29: 85-87.

A laboratory-scale pasteurization system has been developed for the rapid heating and cooling of liquid products such asjuice and wine. The equipment was built with commercially available components and provides fast and accuratepasteurization of small samples (23 L). The system may be operated in two modes; product heated from 0 to 85°C at 4 L/min for hot bottling, and product heated to 85°C then cooled to 20°C at 5 L/min for flash pasteurization.

INTRODUCTION

The purpose of heat processing is todestroy microorganisms; the destruction ofall microorganisms present is called sterilization. This is usally accomplished attemperatures above 100°C. "Pasteurization" means heating at temperatures below100°C and the primary purpose of thisheating is to destroy microorganisms thatare relatively heat sensitive such asnon-spore-bearing bacteria, yeasts andmoulds. The percentage of microorganisms killed is dependent on factorssuch as product type, pasteurization temperature, and duration of heating. The second purpose of this heat treatment is todeactivate enzymes. If this treatment is notdone adequately, there could be signs ofenzymatic spoilage in a microbiologicallystable product. The overall objective ofpasteurization is to ensure that the qualityof the product will remain acceptable aftera lengthy storage.

Continuous processing is superior tobatch processing because it is easier toobtain uniform heating of a liquid productand it is better suited for the requirementsof bottling. This type of system also allowsthe product to be rapidly cooled immediately after pasteurization if hot bottling isnot required. This heating and quick cooling is referred to as flash pasteurization.For these reasons the juice and wine industries favor continuous pasteurizationsystems.

At the Horticultural Research Institute

of Ontario, several small batches of experimental juices and wines had to be preserved for future evaluation. To accom

plish this, a laboratory-scale continuousflow pasteurizer (Fig. 1)was developed forflash pasteurization and hot bottling.

SYSTEM DESIGN

A system schematic diagram of theVineland Mobile Pasteurizing System isshown in Fig. 2. The heart of the system isan Alpha Laval model P20 plate heatexchanger. The product is heated by circulating hot water through the plates of theheat exchanger in a counter-current manner.

Heating SystemHot water was chosen as the heating

medium in the heat exchanger because anelectric heating coil can be used in the casewhere steam is not available. The essential

components of the system are the hot watertank, water pump, and flow control valve.

The hot water is heated by injecting

Figure 1. Mobile juice and wine pasteurizer used for hot bottling and flash pasteurization.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. I, WINTER, 1987 85

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Figure 2. Schematic diagram of pasteurization system. A, stainless steel water reservoir; B, hotwater thermostat; C, steam solenoid valve; D, hot water pump; E, heat exchanger;F, water temperature sensor; G, temperature gauge; H, flow control valve; I, producttemperature sensor; J, temperature controller-recorder; K, air cylinder; L, water reliefvalve; M, product pump.

to temp.

recorder

heated ~juice 85X

PLATE

HEAT

EXCHANGER

bypass tocoolingsection

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temp, sensor tube0

^| relief valve (p)

3-way bottlingvalve @

Figure 3. Schematic diagram of plate heat exchanger and product flowpaths. The heated productis either removed through the bottling valve (N) or bypassed to the cooling sectionthrough valve (Q) to complete the flash pasteurization process.

steam into a coil located inside a 45-L

stainless steel hot water reservoir (A)(Fig. 2). The operating temperature ismaintained by means of an adjustablethermostat (B) that operates a two-way

solenoid valve (C). This valve regulates theflow of low-pressure steam into the coil.When the water reaches its operating temperature, an Armstrong model 4260 centrifugal pump (D) is turned on to circulate

the water through the heat exchanger (E).The water temperature is measured with atemperature sensor (F) as water flowsthrough the system. This temperature ispresented on a panel mounted gauge (G).The flow of hot water is regulated by meansof a Jordan Mark 70 automatic flow control

valve (H). A remote sensor (I) located inthe product outlet line of the heatexchanger senses the temperature of theproduct and transmits it to a PartflowModel RFA temperature controller-recorder (J). This pneumatic controlleractivates the air-powered flow-controlvalve (H) thus regulating the flow of hotwater through the system to match the heatdemand. Compressed air is supplied to thecontroller from a compressed air cylinder(K) equipped with a pressure regulator.The hot water system is provided with arelief valve (L) that protects the heatexchanger from excessive pressures. Themaximum water flow rate can be control

led by means of a ball valve (S) (Fig. 2).For both hot bottling and flash pasteurization the hot water flow rate was set at9 L/min.

Heat ExchangerThe heating surface of the heat

exchanger consists of corrugated stainlesssteel plates clamped together in a frameand sealed at the edges with rubber gaskets. The plates are provided with cornerports arranged so that the two fluids flow inalternate interplate channels, in a counter-current direction.

Maximum working temperature for theheat exchanger is 98°C and its maximumworking pressure is 414 kPa. Maximumallowable flow rates in the heat exchangerare 50 L/min for the heating and coolingmedium and 8 L/min for the wine or juiceproduct. The heat exchanger surface areais 5.25 m2 with a heat transfer coefficientof5.83kW/m2°C.

Product Flow

Adjustable flow of the product isachieved by means of a Waukesha model3DO stainless steel variable speed pump(M) (Fig. 2). This rotor-type sanitarypump has a volumetric displacement of34 mL/revolution and a port size of2.54 cm. Its speed range is 50-500 rpmwith pressures up to 1034 kPa. Speed variation is accomplished using a " V" belt anddual variable pitch pulleys mounted onparallel shafts. Also included in the driveis a helical gear reducer. The flow from therotor pump can be varied by manuallyaltering the pulley diameters on the variable speed drive. Product flows can rangefrom 1L/min to 12L/min. The pump was

86 CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

set to deliver 4 L/min for hot bottling and5 L/min for flash pasteurization.

The product is pumped through a flexible food grade hose to the inlet of the heatexchanger where it is heated to 85°C. During hot bottling the heated product isremoved through a three-way bottlingvalve (N) (Fig. 3). A digital thermometerprobe (O) is inserted in the hot productflow line and provides a visual check of thetemperature.

A relief valve (P) is installed in theproduct flow line to protect the heatexchanger from exceeding its maximumoperating pressure. Also provided in theproduct line is a by-pass valve (Q) thatallows the product to circulate through thecooling section of the exchanger. Productis cooled in the cooling section of the plateheat exchanger by circulating cold tapwater through alternate interplate channels. In this way, rapid cooling of the product to 20°C is achieved. A three-way valve(R) (Fig. 2) is used to flush the heatexchanger with tap water once the productflow has stopped.

PERFORMANCE

Initial problems were encountered withthe pasteurizerdue to rust formation in the

hotwatersystem. This problemwassolvedby substituting steel lineswithcopperpipeand replacing the cast iron pump with abronze centrifugal pump. During preliminary tests with the pasteurizer, theproduct pump would lose its prime andallow the juice to be overheated. This overheating of the product produced foulingand poor heat transfer inside the heatexchanger. As a solution, the plates in theheat exchanger were cleaned and a three-way valve installed so that the productcould be flushed out with tap water. Subsequent tests proved that the system effectively pasteurized fruit juices and wines.

The hot water reservoir size was ideal

for the heating requirements of this low-capacity pasteurization system. Higher orlower pasteurization temperatures could beachieved by adjusting the temperature andflow rate of the heating medium.

DISCUSSION

The pasteurizer was designed and builtto pasteurize samples of grape juice. Thisjuice is pumped out of 25-L bottles,through the pasteurizer, and then into700-mL bottles. This unit was developedin 1982, and tested over a period of 2 yr atthe Horticultural Products Laboratory of

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

our Institute. There was no evidence of

spoilage in the juice after 2 yr of storage.Although the system is only laboratory

size, its capacity can be increased for commercial application by increasing thenumber of plates on the heat exchanger,and by increasing the capacity of the hotwater and product flow pumps. All sensorsand instrumentation controls would

remain essentially the same.

CONCLUSION

This small-scale pasteurizer has provedto work effectively for the pasteurizationof liquid products at a temperature of 85°Cand at a flow rate of 4 L/min. The mobileunit offers a low-cost solution for pasteurization of pumpable products andserves as a test model for a commercial

unit. Tests with the pasteurizer will continue so that further information on its

effectiveness can be obtained.

ACKNOWLEDGMENT

We wish to thank Peter Devlin, Alpha-LavalLtd., for technical advice; Jim Juhlke,H.R.I.O., for his assistance in the constructionof the pasteurizer; and Rod Palabay for his helpin testing the unit.

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