Pasteurization units

A stream of hot water at 85 C and a rate of I kg/s is needed for the pasteurizing unit in a milk-bottling plant. Such a stream is not readily available, and will be produced in a well-insulated mixing tank by directly injecting steam from the boiler plant at 10 bar and 200 C into city water available at 1 bar and 20 C. 

Heinz et al. (2003) focused on improving the energy efficiency of PEFs treatment for pasteurization of apple juice inoculated with E. coli by investigating the relation between the reduction achieved in the survivor count and electric field strength and treatment temperature. To evaluate the thermal load of the product the pasteurization unit and cook value, key benchmarks for the thermal load, were used to compare PEE and conventional heat treatment. 

INSERM U819 Institut Pasteur Unite Pathogenic Virale 25-28 Rue du Dr Roux 7S71A Paris Cedex 15 France... 

Mixed populations of common brewery contaminants, in beer subjected to a range of temperatures of various times, were examined for viability (Fig. 20.22). Typically with temperatures over 50 C (122°F) an increase in temperature of TC (12 6°F) accelerated the rate of cell-kill ten-fold. Thus at 60°C (140°F) the minimum time required for the population to be killed may be 5 6 min, but at 53°C (127 4°F) it would be 56 min and at 67°C (152-6 F) would be 0 56 min. One Pasteurization Unit (PU) has been defined arbitrarily for the beer as the biological destruction obtained by the holding of a beer for one minute at 60°C (140 F). The effect is a product of (/) the lethal rate (djc/d/, where x is the number of viable micro-organisms per wort volume and t is time in min) and (//) the time of application. Thus PU/min = 139 where a is the temperature (in °C) minus 60°C. Pasteurization Units have been shown to be additive in their effects in a complex treatment where temperature... 

Relationships between temperature and lethal rate or pasteurization units per minute of treatment... 

Fig. 20.23 The upper curve represents a sequence of temperatures 8- 2 5°C (46 5-144-5°F) typical of a pasteurization process. The lower curve is the corresponding number of pasteurization units delivered (ordinate 0-3-2). Total pasteurization units = 40.

It has been claimed that the lethal rate is enhanced when carbonated instead of noncarbonated beer is used. The most resistant of the normal brewery contaminants are members of the lactic acid bacteria and certain species of Saccharomyces, e.g. S. pastorianus. Special difficulties attend the pasteurization of returned beer where the level of contaminants may be very high. However since such beer may be filtered before pasteurization and is usually blended into conditioning tank at low rates, the adverse effect on flavour of using a large number of pasteurization units may be discounted. With normal beers, excessive pasteurization leads to cooked, biscuity flavours, especially when the dissolved oxygen content of the beer is high (say in excess of 0-3 mg/1). 

Fig. 9.1. Pasteurization units supplied by a eonstant temperature, according to time and tonperature (Devize and Rib6reau-Gayon, 1977)...

The number of pasteurization units required to obtain a certain level of destruction can be calculated from yeast thermoresistance criteria in a given medium. Laboratory studies anticipated that 0.05 pasteurization units would be sufficient for the destruction of yeasts in a dry wine at 12% vol.ethanol. In practice, 0.5 pasteurization units are required to sterilize such a wine. The uneven heat supplied by industrial heating equipment and the existence of particularly resistant yeast strains at the final stages of fermentation can explain this difference. Table 9.5 shows the necessary conditions for the destruction of germs according to the constitution of the wine. 

Table 9.5. Number of pasteurization units (PU) necessary to sterilize different wines (Devdze and Ribereau-Gayon, 1978)...

In practice, stability is satisfactory if the viable yeast population is less than 1 cell/ml. It might be preferable to set a lower limit (for example less than 1 cell per 100 ml) but in this case the sample would have to be filtered for the germ count. This operation can be very difficult, if not impossible—for example, with new sweet botry-tized wines. The number of pasteurization units required to sterilize a wine in terms of its constitution is given in Table 9.5. The heating time directly depends on the industrial pasteurization flow rate. From the graph in Figure 9.1, the required temperature can be predicted. 

Milk has been a source for food for humans since the beginning of recorded history. Although the use of fresh milk has increased with economic development, the majority of consumption occurs after milk has been heated, processed, or made into butter. The milk industry became a commercial enterprise when methods for preservation of fluid milk were introduced. The successful evolution of the dairy industry from small to large units of production, ie, the farm to the dairy plant, depended on sanitation of animals, products, and equipment cooling faciUties health standards for animals and workers transportation systems constmction materials for process machinery and product containers pasteurization and sterilization methods containers for distribution and refrigeration for products in stores and homes. 

The equipment needed includes a balance tank, regenerative heating unit, positive pump, plates for heating to pasteurization temperature, tube or plates for hoi ding the product for the specified time, a flow-diversion valve (FDV), and a cooling unit (Fig. 4). Often the homogenizer and booster pump also are incorporated into the HTST circuit. 

The balance or float tank collects raw milk entering the unit, receives milk returned from the flow-diversion valve that has not been adequately heated, and maintains a uniform product elevation on the pasteurizer intake. 

Booster Pump. Use of a centrifugal booster pump avoids a low intake pressure, particularly for large, high volume units. A low pressure (>26.6 kPa (200 mm Hg)) on the iatake of a timing pump can cause vaporization of the product. The booster pump is ia the circuit ahead of the timing pump and operates only when the FDV is ia forward flow, the metering pump is ia operation, and the pasteurized product is at least 7 kPa (1 psi) above the maximum pressure developed by the booster pump (Fig. 8). 

Pascal An SI unit of pressure the pressure exerted by the force of 1 newton on an area of 1 square meter, 104,635 Paschen series, 138 Pasteur, Louis, 601 Pauli exclusion principle, 141-143 Pauling, Linus, 185 Pentyl propionate, 596t Peptide linkage The—C—N—group... 

High-temperature short time (HTST) pasteurization is used in a majority of plants in the United States. HTST pasteurization is conducted at temperatures > 72 °C and holding time > 15 s in the United States (FDA, 2009). Milk may also be pasteurized using ultrahigh temperature (UHT) pasteurization. 

In a preliminary study, Tomasula et al. (2009) simulated the fluid milk process to identify energy usage and GHGs associated with HTST pasteurization and the related unit operations, such as homogenization. Physical property data for milk and cream were provided to the simulator. Packaging was not included as part of the simulation. GHGs were... 

Three typhoid vaccines are available currently for use in the United States (1) an oral live-attenuated vaccine (Vivotif Berna-TM vaccine, Swiss Serum and Vaccine Institute), (2) a parenteral heat-phenol-inactivated vaccine (Typhoid Vaccine, Wyeth-Ayerst), and (3) a parenteral capsular polysaccharide vaccine (Typhim Vi, Pasteur Merieux). Immunization is recommended only for travelers going to endemic areas such as Latin America, Asia, and Africa household contacts of a chronic carrier and laboratory personnel who frequently work with S. typhi.13... 

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