Steam sterilization is the main form of canned high temperature sterilization. With the continuous popularization of automatic sterilization pots, many sterilization technicians only know the operation equipment, but they do not necessarily understand the original method and final purpose of each step of steam sterilization. It is only necessary to master the original steam sterilization method steps, and it is possible for the sterilization technician to correctly evaluate whether the sterilization program setting is scientific and reasonable.
1, start sterilization
After all the exhaust valves and the vent valve are fully opened, steam is introduced. All bleed valves should always be open during the entire sterilization period .
2, exhaust
After steaming, the exhaust valve must be opened until the specified time and temperature are reached to ensure that all air in the sterilizer is drained. If the exhaust is not complete; there is still air left in each area of ​​the canned food in the sterilization pot, which will result in insufficient sterilization.
During the venting process, the drain valve at the bottom of the sterilizing pot should be opened from time to time in order to discharge the condensed water accumulated in the initial stage of the exhaust gas or the remaining cold water . The purpose of opening the drain valve is not to vent. Unless there is a special regulation in the exhaust method, the drain valve at the bottom of the pot should be closed after the water is discharged, without obstructing the exhaust.
The exhaust must use an accurate timepiece or timer to calculate the exhaust time, but not the recorder's chart. The exhaust temperature should be measured in accordance with the glass mercury thermometer display. When the exhaust temperature and exhaust time both meet or exceed the specified limits, the exhaust valve can be closed and the temperature and time must be recorded. The exhausting method and technical requirements for various standard constructed sterilization pots are described in 2.2.10 "Exhaust Specifications" in the first chapter of this book.
3, heating time
The temperature rise time refers to the stage from the entry of the steam until the sterilization temperature is reached, and can be maintained until the start of sterilization, including the exhaust time. If a steam bypass is used, the bypass valve should be gradually closed after the sterilization temperature is reached to prevent a sudden drop in temperature.
The proofreading temperature recorder is the same as the glass mercury thermometer. When the sterilization temperature is stable, these readings must be recorded.
4, sterilization timing
The sterilization time can only be calculated after the sterilization pot has been fully vented and the mercury thermometer has reached and stabilized at the sterilization temperature. The sterilization temperature can only be represented by a mercury thermometer, not a pressure gauge. Sterilization time should be timed with an accurate clock or timer, and no watch or other recorder chart can be used.
5, the end of sterilization
Check the following items before turning off the steam:
(1) Check with a clock or an accurate timer to determine if the specified sterilization time has been reached.
(2) Check the recorder chart to see if the specified sterilization time is recorded.
(3) Check the recorder chart to see if there is any temperature fluctuation below the specified sterilization temperature.
(4) Check the mercury thermometer to see if it indicates the specified sterilization temperature.
If any dissatisfaction is found in the above inspection, appropriate measures should be taken to ensure complete sterilization.
If you are satisfied with the above checks, you can turn off the steam.
6, cooling and storage
When the can is cooled, the duration of the water cooling phase should be sufficient to reduce the average temperature of the can contents to about 38 ° C, but the degree of water cooling should not be excessive and cause the surface of the can to rust. In a humid environment, if the water is cooled to about 38 ° C, it may cause the surface of the can to rust. In this case, the can should be mechanically dried, or the water can be stopped when the temperature of the contents of the can reaches a temperature of about 49 ° C, and then cooled with sufficient air before the can is placed in storage. If the actual temperature of the contents of the can is above 38 ° C, the cans are densely stacked together or placed in the box, because the slow cooling will cause canned spoilage caused by thermophilic bacteria, and due to heat Damage to product quality.
The cooling of the cans can be different depending on the tank type and the sterilizer structure and other factors. If recirculating cold water is used or cooled in a sink, the cooling water must be chlorinated or otherwise disinfected and the residual amount of disinfectant measured at the drain of the cooling system.
In order to prevent deformation and sag of the bottom cover of some cans, pressurized cooling is required . For a special can container, a detailed and appropriate cooling method can be studied with an empty can manufacturer.
Before the overflow valve, drain valve or exhaust valve is opened, the pressure of the sterilizing pot has dropped to zero. If water is injected into the sterilizing pot, the steam will condense due to the water, which will cause a vacuum in the sterilizing pot, resulting in a vacuum. Deformation of the can or damage to the sterilization pot.
6.1 Cooling in the pool
(1) Open the overflow valve, drain valve or exhaust valve to eliminate the steam in the sterilizer and reduce the pressure to zero.
(2) Slowly open the inlet valve at the top and spray water to the can for about one minute to remove some heat.
(3) Lift the sterilization basket from the sterilization pot to the cooling pool.
This method is suitable for vertical sterilization pots. The great advantage of using a cooling pool is that the sterilizer is reused as soon as possible. Usually the cooling pool is not used with a horizontal sterilizer.
6.2 Normal pressure cooling in the sterilization pot
(1) Open the overflow valve, drain valve or exhaust valve to remove all the steam in the sterilizer and reduce the pressure to zero.
(2) When the pressure drops to zero, close the drain valve, but do not close the overflow valve or the exhaust valve, then slowly open the top inlet valve and fill the sterilizer with water.
(3) When the sterilizer is filled with water, close the inlet valve at the top and then open the inlet valve at the bottom. At this point the water flows from the bottom to the top and is discharged through the overflow tube. After cooling for a few minutes in this way, close the bottom inlet valve and open the drain valve and the top inlet valve to allow the water to flow in the opposite direction. If the retort is not equipped with an overflow tube, let the water enter the sterilizing pot from the top and drain it from the drain (but keep the water in the sterilizer), so that even cooling can be obtained. The length of time required to complete the cooling process depends on factors such as water temperature, tank type, and type of canned product.
6.3 Pressure cooling with steam and water
This cooling method is to pass steam to the top of the sterilizing pot to maintain the pressure, and let the cold water slowly flow from under the hot water layer to the bottom of the sterilizing pot, thus preventing the steam from being condensed into condensed water. The hot water layer is obtained by connecting the steam pipe to the inlet pipe at the bottom and heating the cold water introduced first for a minute. The cooling procedure can be carried out as follows:
(1) After the sterilization is finished, close the vent valve, close the inlet valve at the bottom, and open the inlet valve at the top to make the pressure in the sterilizer exceed the pressure at the time of sterilization by about 0.14kg/cm2 (0.014Mpa).
(2) Open the inlet valve connected to the bottom inlet pipe, and then slowly open the inlet valve at the bottom so that hot water can be injected into the sterilization pot.
(3) Continue to pass steam and water until about one quarter of the sterilizer is filled with hot water, then turn off the steam and pass cold water under the hot water layer.
(4) When injecting cold water into the sterilization pot, slowly turn off the inlet valve at the top, but keep the pressure in the sterilization pot stable.
(5) The pressure in the sterilizer is maintained at or slightly greater than the pressure at the time of sterilization until the sterilizer is almost filled with water and immersed in the can.
(6) Zui is good to install a small faucet near the top of the sterilizer to know when to reach the water level. When the water level is close to the top, slowly open the overflow valve or drain valve and start to close the small inlet valve, taking care to keep the pressure in the sterilizer on the specified standard. If the sterilizing pot is filled with water at a high inlet pressure and is not drained and drained in time, the pressure of the sterilizing pot will quickly rise to the water pressure, which will cause damage to the can and the sterilizing pot.
(7) Appropriately balance the bottom water inlet and the upper overflow drain to maintain the sterilizer at a specified pressure until all the cans are sufficiently cooled to avoid deformation and lobes of the can lid.
(8) Continue to open the large overflow drain valve and gradually reduce the pressure.
(9) Then enter the cold water from the bottom and drain through the overflow pipe; after a few minutes, in turn, the water is drained from the top and drained from the lower drain pipe. At this time, the sterilizer is filled with water, and the counterflow can be canned. Cooling more evenly.
6.4 Pressurization with air and water
(1) After the sterilization is completed, close all the vent valves and open the compressed air valve so that the pressure in the sterilizer exceeds the pressure at the time of sterilization by about 0.14 kg/cm2 (0.014 MPa).
(2) Turn off the steam.
(3) Slowly pass cold water to the top or bottom of the sterilization pot and use compressed air to maintain the pressure in the sterilization pot.
(4) Zui is good to install a small faucet near the top of the sterilizer to keep abreast of the time when the water level reaches this height. As the water level approaches the top, gradually open the overflow or drain valve, close the air valve, and adjust the inlet valve to maintain the sterilizer pressure at the specified level. If the sterilizer enters the water with high water pressure and does not discharge a part of the water in time, the pressure in the sterilizer will rise rapidly to the pressure of the inlet pipe, which will cause damage to the can and the sterilizer. .
(5) Properly balance the influent and draining to maintain the sterilizing pot at the specified pressure until all the cans are sufficiently cooled to avoid deformation or lobes of the can bottom cover.
(6) Open a large relief valve or drain valve to gradually release the pressure.
(7) Regardless of the water entering from the top or from the bottom, the drainage position is opposite to the inlet position, and this countercurrent helps the can to cool more evenly.
6.5 air cooling
If the water-cooling equipment has limited capacity or if there is a shortage of water supply, then air cooling must be used. The cans are stacked in a single row, allowing the air to circulate freely between rows and rows. The arrangement of the cans per stack should be in the ventilation section of the warehouse, and carefully eliminate some of the factors affecting the circulation of air, which will help prevent the heat and addiction of the cans. Hot bacteria are spoiled. When using air cooling, it is necessary to prevent the can from coming into contact with contaminated ground.
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