Ngoài sự cần thiết cho container xuất hiện đầy đủ, headspace là cần thiết để mở rộng nhiệt, gây ra bằng cách đốt các sản phẩm từ làm đầy nhiệt độ để xử lý nhiệt độ, không kết quả trong một xây dựng quá nhiều áp lực và thiệt hại với con dấu kín. Trong những trường hợp bình thường seams chịu được các chủng được tạo ra bởi áp lực nội bộ, Tuy nhiên, trong trường hợp cực kỳ, điều này gây ra biến dạng vĩnh viễn (được gọi là peaking. hoặc sự oằn) có thể kết thúc. Đạt đỉnh điểm là không thể chấp nhận, vì nó mang với nó một nguy cơ liên quan các đường may trong vùng lân cận thiệt hại sẽ rò rỉ và cho phép xâm nhập của chất gây ô nhiễm, đặc biệt là trong quá trình làm mát khi các lon vẽ chân không. (Áp lực quá mức xây dựng trong thùng chứa bằng kính trong tiến bộ nhiệt sẽ thường đánh bật nắp.) Kể từ khi đạt đỉnh điểm là một hệ quả của quá nhiều áp lực nội bộ thuộc có thể, nó có thể được ngăn chặn bằng cách kiểm soát một số yếu tố khác hơn là headspace, này bao gồm: điền vào nhiệt độ; cao hơn nhiệt độ làm, càng ít áp lực tạo ra bằng cách đốt các nội dung để xử lý nhiệt độ. Như một consequence của bể điền một hình thức chân không trong container sau khi xử lý nhiệt và làm mát; Máy hút đóng cửa; lon và bình thủy tinh có thể đóng cửa dưới chân không có tác dụng chống lại sự gia tăng áp lực gây ra bằng cách đốt các sản phẩm trong một hộp kín. chân không đóng cửa là đạt được bằng cơ khí di tản container headspace khí ngay trước khi niêm phong, hoặc bởi đóng, dòng chảy hơi một quá trình trong đó hơi nước nóng siêu đỏ ửng trên đầu trang của container ngay lập tức trước khi có thể đóng cửa cuối hoặc chai được bịt kín tại chỗ.3.5 SealingTechniques for formation and the evaluation of the hermetic seals with metal cans, glass containers and laminated systems are described in Chapter 2. Central to the success of the entire fish canning industry is the ability of canners to form hermetically sealed containers whether they be made of metal, glass or laminates of plastic and/or plastic and foil. Failure in this critical operation will mean that product safety and shelf stability is at risk. Given the potentially serious implications of seal failure and post-process contamination, manufacturers must be sure that their operations are strictly monitored at regular intervals throughout the entire production. Once sealing machines have been adjusted, suitably trained personnel must confirm their: satisfactory performance by examination of sealed containers. There is ah abundance of literature available from packaging material and sealing machine suppliers recommending methods of seal formation and criteria for their evaluation. In several countries regulatory authorities have published procedures for the evaluation of seal adequacy; the purpose of this is to ensure that not only local manufacturers have guidelines to follow, but also so that foreign manufacturers can comply with the requirements of the country to which they are exporting.Since formation of sound hermetic seals is critical, it is essential that records confirming compliance with GMP guidelines are completed during production, and maintained after release of the product. If in the event of a product recall there are no permanent records, manufacturers run the considerable risk of being unable to demonstrate that their operations were in control, and that due care was taken to assure the safety of the finished product.It is important that sealed containers be indelibly coded with details of the production date and time, product codes, the manufacturing plant. and any other information that is necessary to identify the origin and nature of the product.3.6 RetortingProcedures for developing and controlling delivery of thermal process schedules are outlined in Chapter 1, and descriptions of available retorting systems are in Chapter 5. However, no matter how well the scheduled process has been formulated, nor how great the capital expenditure for buying top quality equipment, these efforts will be wasted if there is human error in delivery of the process.3.6.1 Retort operating procedures for CansIn order to reduce the risks of operational errors, it is customary to adopt standard procedures for retort operation. In some countries the regulatory authorities require that supervisors of retort operations in those plants manufacturing low-acid canned foods shall have successfully completed a specialized training course in the principles of thermal process control. One of the objectives of these courses is to provide retort supervisors with standard operating procedures which will reduce the risk of error being made through ignorance or carelessness.As a guide, and as a means of standardising procedures, it is recommended that retort operations be classified according to the five sequential steps shown in Table 6. Also shown is a checklist of key points for each stage in the retorting procedure. The five stages of retorting are intended to apply specifically for processing cans (loaded in retort baskets) in steam and pressure cooling in conventional retorts; the sequence will need to be adapted if processing glass (see sections 3.6.2 and 5.3.7) or if processing cans in crateless retorts (see section 5.3.6). As discussed previously, GMP regulations require that the retort operator must record on the retort log sheet (see Figure 5) all processing details for each batch processed.
Table 6 The five stages of retorting a/ and key point checklist
Stage Checklist
1. Preparation and loading: Is the retort drained?
Are all containers removed?
Are air and water injects closed?
Are cans loaded and the process commenced within one hour of filling?
Are heat Sensitive indicators attached to retort baskets?
2. Venting: Is all the air removed?
Does indicating thermometer register retort temperature of > 103 °C?
3. Come-up: Is it > 10 min for fully laden retort?
4. Processing: Is retort at scheduled operating; temperature for the scheduled process time?
Is process timing, commenced when retort reaches operating temperature?
If there are any deviations from the scheduled process are containers from the batch isolated?
Is there agreement between scheduled process time and thermograph record of process tittle?
Are bleeders open during the process?
Is condensate drain open and operating?
5. Cooling: Is steam removed from retort before cooling water enters?
Does the cooling water fill the retort within 10 min?
Is the retort pressure cooled to prevent cans peaking?
Is the pressure cooling controlled to prevent panelling?
Is the cooling water of suitable micro-biological quality? b/
Is cooling water chlorinated so that there is a detectable level of free available chlorine at the completion of cooling?
Are cans rapidly cooled to centre temperatures > 40 °C?
Are there procedures to preclude manual handing; of wet containers?
a/ These guidelines are based on the operation of a static batch retort in which heating is with saturated steam and cooling is with an over-riding air pressure
b/ As a guide, suitable retort cooling water win have no detectable coliforms in 100 ml samples taken monthly, and have a total aerobic colony count of < 100 organisms/ml for samples taken weekly
3.6.2 Retort operating procedures for glass
Although many of the key points identified in Table 6 will apply equally to processing cans and to processing glass in water, it is important to make clear the distinction between the two systems. The two features about retorting glass that make the operation different from that for cans are the use of water as the heating medium and the need for over pressure. It is common practice when using vertical retorts to lower the baskets into pre-heated water. Pre-heating the water reduces the time required to bring the entire system up to operating temperature, and it also prevents thermal shock breakage that could follow if hot filled jars were immersed in cold water. The temperature of the water must be strictly controlled so that it does not exceed that of the product, otherwise the partial vacuum holding the cap in place may be lost, or sufficiently reduced for the seal to loosen or vent: if struck. Another reason for controlling the water temperature is that if permitted to fall, it will cause a drop in the initial product temperature and possibly lead to underprocessing.
In horizontal retorts, because the baskets cannot be added directly into pre-heated water, it is necessary to load the retorts while empty and then add the water. If possible the water should be pre-heated so that it: is added at approximately the same temperature as the product.
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