CPP Low Water Activity Food Pasteurization
The “Controlled Pasteurization Process” pasteurization system (CPP) is a pasteurizer that can be used to pasteurize (in-shell, raw & salted/roasted) tree nuts, peanuts, seeds, flour, grain, herbs and spices. The system can be installed in line with existing (continuous belt) roasters.Advantages of the CPP system:
• Guaranteed 5 log reduction
• In line, fully automated process
• No discernible change to organoleptic properties
• Chemical free natural and safe process
• Complies with organic standards
• Final moisture content standardization
• Exterminates infestations
• Capacities range from 500 up to 40,000 lbs/hr
• Easy change over between different products
• Very low operational costs
• Also suitable for granular and powdered products
Pasteurization in an equilibrium
Water activity influences pasteurization kinetics and heat resistance of microorganisms. Several scientific research works investigated the influence of substrate water activity on inactivation of bacteria with dry heat. Chiewchan (2007) reported an increasing heat resistance of Salmonella at decreasing water activities. This effect was even more pronounced when the bacteria were fixated to the surface of a rawhide product and dry heat was directly applied to the rawhide.
With actual pasteurization systems the application of steam is used. At normal pressure (i.e. 100ºC), inactivation of Salmonella will be log 2.05 – 3.83 after 35s by steam treatment. By increasing the treatment time up to 65s, the log reduction increases further to 4.00 – 5.72, but the moisture uptake progressed considerably, so the treatment duration has to be limited to 35s. However, this indicates that the application of humid heat improves heat inactivation considerably due to several reasons: First, the heat capacity of water vapor is very high and even exceeds the heat capacity of water at the same temperature; Secondly, if the surface temperature is below dew point temperature of the atmosphere, water vapor condenses on the product surface and penetrates in cavities and crevices. Finally, surface condensation increases water activity on the surface and therefore reduces heat resistance of microorganisms.
Consequently, an ideal pasteurization process for spices, grain, flour, seeds and nuts includes the application of moist heat under conditions, at which the condensation of moisture on the surface is limited to an extent, at which a high water activity is established and a sufficient heat transfer is realized to achieve the necessary microbiological inactivation. Such conditions can be realized when:
1. The product surface temperature is slightly below the evaporation temperature at the beginning of the thermal inactivation phase, so only little moisture condenses on the product surface increasing the product temperature quickly to the evaporation temperature.
2. The conditions at evaporation temperature are maintained for an effectual duration. At evaporation conditions, no additional moisture condenses on the surface, and virtually no surface moisture is lost due to evaporation. Therefore, ideal inactivation conditions at high water activity are maintained.
3. Finally, after the humid atmosphere treatment is finished, excess moisture is removed from the surface in order to re-establish the native state of the product.
Product flavor and properties are susceptive to changes when heated to increased temperatures. Therefore, it is essential to carry out such treatment at reduced pressure in order to reduce evaporation temperature. Furthermore, in order to avoid excessive moisture condensation on the product surface during the pasteurization treatment, it is essential to preheat the product to a temperature slightly below evaporation of the system.
The CPP pasteurizer consists of a pressure vessel with a central mixing system. The pressure vessel has to be insulated to avoid energy loss and condensation during the pasteurizing process.
First, the product is preheated in a separate process. Then the product is filled into the vessel, equilibrated and pasteurized in a humid atmosphere. After pasteurization, small quantities of residual moisture are removed in a vacuum at the same temperature. Finally, the product is cooled and packed or further processed.