Product pasteurisation consists in micro-organisms inactivation by means of heating. This kind of process is called "exponential". It progressively reduces their number as temperature and holding time raise. Keeping the product at a given temperature is achieved through the holding pipe, a very long tubular duct where heated liquid flows and keeps the high temperature for 210 seconds. After bacteria has been inactivated by heat, it is very important to immediately chill the product at +3/4°C. in order to slow down the reproducing activity of the very few left bacteria colonies.


Modern pasteurization happens in “continuous flow” which means that the product never stops during heat treatment from entrance to outlet of the plant. Proper positive pumps will assure that the flow is kept smooth and constant during the complete production batch.
A previous technology, still used today in low-quality or mini size plants, consist in heating up the raw liquid egg placed inside a storage tank and then cool it down while still in the same tank. This method, called “batch pasteurization” is very economical because it does not require expensive piping, pumps and heat exchangers. All process happens inside a special tank whose walls and bottom can be heated or cooled down with proper water recirculation. The main problem related to this technology is quite easy to understand. Heating up and cooling down a big amount of product standing inside a big tank requires a lot of time. Therefore there will be a long time during the process where the liquid will be slowly warming up from 30° to 64° C and then back to 4°C. The longer the product is exposed to the “perfect” incubation tempeature (35-37°C), the more the bacteria will reproduce. So before “inactivating” the bacteria the process strongly promotes their reproduction and, on the same way, after “inactivation”, the few bacteria left will get a very good chances to reproduce before reaching the safe temperature of +4°C. So the final product coming out from such technology can only have higher bacterial charge compared to continuos flow pasteurization.


In a “continuos flow” system, the needed heating of the product is achieved through a plate or tubolar heat exchanger. Hot water is produced by an external boiler, its temperature is finely adjusted to a precision up to 0,2°C and then sent to the heat exchanger. If it is a plate heat exchanger, on one side of the plates hot water will flow and on the opposite side the raw egg. The two liquids will be exchanging their tempeature and the egg will be warmed up to +64°C temperature. After heating the product will flow for a minimum time of 210 seconds inside the “holding pipe” to allow the bacteria get inactivated. After this time the product returns to the heat exchanger where chilled water is quickly bringing its tempeature down to +4°C. Heating up and cooling down process will take less than one minute, that’s why there is no time for the bacteria to restart reproduction.

Normally to reduce environmental impact and energy costs, the heat exchanger is equipped with an independend section for heat recovery. The principle is to use part of the heat coming from the pasteurized product to pre-heat the incoming raw egg and viceversa for the pasteurized one which must be pre-cooled before the chilling section.


An automatic safety system, in conformity with European rules, deviates and recycles pasteurised product back to the starting point, in case its output temperature is lower than safety temperature set. For this reason the water temperature and product-in-pasteurization temperatures are monitored and recorded constantly and in real time during the whole process.

A pasteurisation process properly completed at correct temperatures allows to remove more than 99,99% of the total bacterial load and 100% of pathogenous bacteria possibly present at the very beginning. Obviously, the end-product quality is strictly linked to the starting quality of the shell egg and the general way to handle each single process inside the facility.

Because of the fact that the egg proteins start to denaturate and coaugulate at very low temperatures (around 66°C), the tempeature cannot be raised more, unless by using tubolar heat exchangers at very high pressures. Not all the bacteria can be inactivated at these temperatures, only thermophilis bacteria and some common salmonellae for sure will be inactivated at 64°C, other bacteria present in the raw liquid could resist and still be present in the end product. Entherobacteriacee, Coliforms, Staphilococci and other pathogenous can seriously harm the health of the consumers if not properly monitored. This point is very important to understand how critical is to adopt very strict hygienic parameters and actions throughout the whole process inside the factory. It will be not only the good quality of the machines but also the starting quality of the raw materials, the proper behaviour of the operators, the respect of the strictest rules of hygiene, the implementation serious HACCP plans which will alltogether assure that the final quality of the product is perfect.