High pressure processing 435 long exposure times. As a consequence, to achieve sterility with minimal impact on nutrition value, flavour, texture and colour, high pressure processing using multiple high pressure pulses and achieving an end temperature above 105oC under pressure for a short time has been proposed(Meyer et al, 2000; Krebbers etal,2001) 21.3 High pressure technology and equipment for the food industry High pressure technology has been used in the industrial production process of ceramics, metals and composites in the last three decennia. As a result, today, high pressure equipment is available for a broad range of process con- ditions, i.e. pressures up to 1000MPa, temperatures up to 2200C, volumes up to several cubic meters and cycling times between a few seconds and several Since high pressure technology offers advantages in retaining food quality attributes, it has recently been the subject of considerable interest in the food industry as a non-thermal unit operation. High pressure equipment with pressure levels up to 800 MPa and temperatures in the range of 5 to 90C(on average)for times up to 30 minutes or longer is currently available to the food industry The actual high pressure treatment is a batch process. In practice, high pres- Ire technology subjects liquid or solid foods, with or without packaging, to pres- sures between 50 and 1000 MPa. According to Pascals principle, high pressure acts instantaneously and uniformly throughout a mass of food and is independent of the size and shape of food products. During compression, a temperature increase or adiabatic heating occurs and its extent is influenced by the rate of pressurisation, the food composition and the( thermo)physical properties of the pressure transfer medium. The temperature in the vessel tends to equilibrate towards the surrounding temperature during the holding period. During pressure release(decompression), a temperature decrease or adiabatic cooling takes place In high pressure processing, heat cannot be transferred as instantaneously and uniformly as pressure so that temperature distribution in the vessel might become crucial. During the high pressure treatment, other process parameters such as treatment time, pressurisation/decompression rate and the number of pulses have to be considered as critical L. Two types of high pressure equipment can be used in food processing: con- entional batch systems and semi-continuous systems. In the conventional batch systems, both liquid and solid pre-packed foods can be processed whereas only pumpable food products such as fruit juice can be treated in semi-continuous systems. Typical equipment for batch high pressure processing consists of a cylin drical steel vessel of high tensile strength, two end closures, a means for restrain ing the end closures(e g a closing yoke to cope with high axial forces, thread pins),(direct or indirect) compression pumps and necessary pressure controls andlong exposure times. As a consequence, to achieve sterility with minimal impact on nutrition value, flavour, texture and colour, high pressure processing using multiple high pressure pulses and achieving an end temperature above 105°C under pressure for a short time has been proposed (Meyer et al, 2000; Krebbers et al, 2001). 21.3 High pressure technology and equipment for the food industry High pressure technology has been used in the industrial production process of ceramics, metals and composites in the last three decennia. As a result, today, high pressure equipment is available for a broad range of process con￾ditions, i.e. pressures up to 1000 MPa, temperatures up to 2200°C, volumes up to several cubic meters and cycling times between a few seconds and several weeks. Since high pressure technology offers advantages in retaining food quality attributes, it has recently been the subject of considerable interest in the food industry as a non-thermal unit operation. High pressure equipment with pressure levels up to 800 MPa and temperatures in the range of 5 to 90°C (on average) for times up to 30 minutes or longer is currently available to the food industry. The actual high pressure treatment is a batch process. In practice, high pres￾sure technology subjects liquid or solid foods, with or without packaging, to pres￾sures between 50 and 1000 MPa. According to Pascal’s principle, high pressure acts instantaneously and uniformly throughout a mass of food and is independent of the size and shape of food products. During compression, a temperature increase or adiabatic heating occurs and its extent is influenced by the rate of pressurisation, the food composition and the (thermo)physical properties of the pressure transfer medium. The temperature in the vessel tends to equilibrate towards the surrounding temperature during the holding period. During pressure release (decompression), a temperature decrease or adiabatic cooling takes place. In high pressure processing, heat cannot be transferred as instantaneously and uniformly as pressure so that temperature distribution in the vessel might become crucial. During the high pressure treatment, other process parameters such as treatment time, pressurisation/decompression rate and the number of pulses have to be considered as critical. Two types of high pressure equipment can be used in food processing: con￾ventional batch systems and semi-continuous systems. In the conventional batch systems, both liquid and solid pre-packed foods can be processed whereas only pumpable food products such as fruit juice can be treated in semi-continuous systems. Typical equipment for batch high pressure processing consists of a cylin￾drical steel vessel of high tensile strength, two end closures, a means for restrain￾ing the end closures (e.g. a closing yoke to cope with high axial forces, threads, pins), (direct or indirect) compression pumps and necessary pressure controls and High pressure processing 435