In this section, we are happy to share our knowledge in the particular field of heat treatments, which we apply on a daily basis.
Here are some definitions concerning our core business:
To be fully operational, a Deflection sensor must be able to be installed on all sides of the packaging, without exerting mechanical stress (a spring system is to be avoided) and have a wide measuring range.
The Delta P calculation represents the pressure stress mechanically supported by the walls of a package during a heat treatment, according to the formula:
Delta P = Pressure in the packaging – retort pressure
Delta P = Internal Pressure – External Pressure
The variation of delta P comes from several parameters:
• the variation of the external pressure (pressure schedule)
• the variation of the temperature, which induces a variation of the internal pressure by expansion, vaporization (in the heating phase) or condensation / retraction (in the cooling phase).
Notes on Delta P behavior:
• For rigid packaging (jar or small diameter metal box), a decrease in the amount of gas initially enclosed in the packaging will increase the final value of the Delta P in case of heating.
• For semi-rigid or flexible packaging (large diameter metal box or plastic container), reducing the amount of gas initially enclosed in the packaging will decrease the final value of the Delta P in case of heating.
• Warning: for a flexible packaging (plastic container), the Delta P loses its relevance. In fact, it would take a very large deformation of the heated packaging to perceive a variation of pressure. In general, the packaging is denatured before displaying a significant variation of the Delta P. The exploitable indicator is then Delta D (packaging Deformation)
As with domestic microwave ovens, the presence of metal can generate destructive electric arc, especially for electronic equipment. Introducing an on-board sensor, containing metallic components, in order to take a temperature measurement therefore looks like a challenge.
Until recently, the only way to measure temperature was to use fiber optic probes. This device offers precise measurements but is difficult to accommodate continuous equipment and is always a delicate implementation. Its use is generally limited to development services, especially as its cost remains high.
After a significant development on the extreme miniaturization of on-board electronics and the geometry of protective boxes, AXITHERM is proud to offer you recorders compatible with all microwave processes today. The range of AXImiWave sensors makes it possible to cover all the control and development needs for products treated by microwave, conventional heating or combined system.
Axitherm offers an original schedule construction approach, the so-called OTTA method, which best preserves the organoleptic and nutritional qualities of the recipe. It should also be noted that this approach maintains the entire production capacity of the retort.
To exploit the data transmission by radio in an retort, a cooking cell, or any other metallic and closed equipment, 2 methods are then possible: 1- Radio transmission inside the enclosure, then wired via the receiving antenna, the cable of which will pass through the metallic wall. The receiver is thus placed outside the equipment and can directly attack a display, a computer or a network. 2- Wired data transmission from inside to outside the enclosure, then a radio relay to the distant operating point (display, computer, network, ...).
The first method is attractive because it makes it possible to instrument retort with automatic loading, but has some limitations:
- high additional cost compared to wired sensors
- significant limitation of the number of sensors used simultaneously in the instrumented enclosure
- risk of communication breakdowns with rotary retort due to many metallic parts inside
The second method requires human intervention to connect the probe after charging but also has its advantages:
- no additional cost compared to fully wired probes
- up to 6 probes used simultaneously in the instrumented enclosure
- possibility of working in supervision on several enclosures
- no risk of communication breakdown.
AXITHERM offers you the 2 equipments to best meet your working methods.
- for temperature measurement in a rotary retort, the accuracy observed with wired thermocouple probe using a rotary connector is extremely questionable (possible drift of several degrees), so we recommend wired PT100 probes or miniature temperature loggers or radio principles described above
- if real time is not essential, miniature temperature loggers are undoubtedly the most economical, precise, reliable and practical equipment to install simply because they do not need to get through to packaging unlike to the other 2 technologies.
In industrial reality, it must be recognized that this is only rarely the case; that schedule X rarely lasts the same duration when the retort is full or partially loaded.
The art of the programmer is to ensure that the schedule is always identical with the desired Fo / PU and the desired packaging aspect. The program which is nothing else a matrix of figures (time, temperature, pressure and sometimes speed of rotation, heating or pressure variation) translates the temperature and pressure profile expected from the retort. Profiles which will only be produced if they are in agreement with the performance of the equipment, energy networks and industrial filling dispersions (packaging and retort). Not so simple! When validating a schedule, it is therefore essential to carry out the temperature control in the most unfavourable conditions because the results will often be different from the standard case. We then see that the retort under partial load is commonly much more critical than under full load contrary to what is imagined. Important note: Most modern retorts have several parameters to manage pressure and temperature controls. These parameters are implemented by the installer and their function is to standardize the behaviour of the different retorts in presence (layout in relation to energy networks, load, design differences, etc.). Here, we understand that the quality of this setting is essential to ensure that the same schedule will give the same result on all retorts. Conversely, an obsolete or incorrectly calibrated setting will generate significant differences between retorts and therefore a dispersion of quality and Fo/PU.
This term is sometimes used to include the various studies and possible measures to control a heat treatment which are:
-The Thermal Mapping in open or closed enclosures (cell, tunnel, oven, sterilizer, retort …)
-The Heat Penetration in a packaged or unpackaged product
-The Schedule Validation to confirm the correct writing of the schedule.
It is therefore necessary to specify its nature. We use the above terminology to avoid confusion.
The goal of this Thermal Mapping is to locate the hot spot and cold spot of the equipment. To do this, we follow the temperatures in the enclosure at different hights. The distribution of the logger is established so as to study the entire volume of the charge treated. It is recommended to have a minimum of 3 loggers per basket. It allows the automatism to be studied completely (Controller setting) as well as ensuring compatibility between the product loading plan and the performance of the retort.
– depending on the design of the equipment, the study must be carried out with a partial load or following a load break (continuous sterilizer). These conditions can exacerbate the cold spot as well as the hot spot.
– although this mapping offers interesting results, it is recommended to validate them on several packaging sizes before being able to generalize. Indeed, the position of the retort cold spot can change with a modification of the loading plan, a new packaging geometry, a new schedule or even an adjustment of the rotation speed
The final objective of a Termal Mapping is to obtain a spatial representation of the temperature dispersion prevailing in the chamber to compare them with a previously defined acceptance grid. The first expected response from a Thermal Mapping is therefore approval to put the studied equipment into operation.
Our experience has shown us that a thermal mapping could result in a delicate observation: the acceptance criteria are not met!
“Thermal Mapping in Retort” is an exclusive developed by AXITHERM to avoid being blocked by this distressing finding.
The information obtained makes it possible to describe not only the uniformity in temperature of the enclosure, but also in heat transfer; that is, the ability of the equipment to heat and cool the load evenly. Explanation: air, steam, water or a mixture of these elements brought to a given temperature will not provide the same energy to the product. In the case of a mixture (air / steam or water / air / steam), the variation of the different proportions of the mixture induces significant fluctuations in the heat transfer potential. So, if the proportions of the mixture change with the position in the load (very frequent case), the heat transfer potential will also change. These differences in heat transfer potential directly impact the dispersion of PU and Fo. This is particularly true for small packages or products with convective heating. This dispersion is inherent in the packaging / processing equipment / schedule combination.
The level of precision of the Heat Penetration makes it possible to qualify the reproducibility of the cycles and to define the operating limits of the devices with regard to the products treated. When it is carried out on actual recipe, it also specifies the following information: • the minimum Fo or PU and its location => essential for the bacteriological validation of the schedule . • the maximum Fo or PU and its location => advantageous for validating the organoleptic acceptance of the product and making it possible to fix claims, in particular on the nutritional qualities of foods • the difference between minimum and maximum Fo or PU => assessment of the overall control of the process (filling, closing dispersions, integration of waiting time, construction of the schedule, ...)
This study is cumbersome to set up but offers the advantage of calibrating bacteriological results with your method and measuring instruments. It is therefore essential information to calmly develop new recipes and the basis for optimizing your schedules.
Here, the values of Tref and Z are adapted to the microorganism that we particularly wish to study. There are thus a large number of possible PU calculations depending on the Tref and Z values used. The couple Tref = 70 and Z = 10 ° C is very common; the target PU is generally 1000 minutes for a DLC of 42 days. It is important to specify the values of Tref and Z as soon as one makes comparisons under penalty of gross errors.
The values Tref = 121.1 ° C and Z = 10 ° C are imposed for the calculation of Fo; they correspond to a reference germ: Clostridium Botulinum. By extension, we can say that: 1 minute spent at 121.1 ° C gives 1 point of Fo. Each product to be treated has a specific microbial load, varied in gender and number. It is therefore advisable to apply a suitable minimum Fo in order to guarantee industrial sterility (Fo = 3 is used as a minimum value by the FDA). Conversely, the organoleptic qualities of a produce are often degraded by an excess of heat and therefore of Fo. Mastering the quality of raw materials is therefore essential to guarantee the stability of products sensitive to cooking phenomena. The accuracy of the Fo calculation is directly linked to that of the temperature measurement, from which it derives. The errors of temperature measurements have mainly 3 origins:
• positioning of the logger (error in tens of ° C = cold spot error)
• geometry / dimension of the probe (error in ° C = unsuitable control equipment)
• probe accuracy (error in tenths of ° C = expired calibration)
Note that the impact of the metrological quality of the probe is practically negligible compared to the impact of its dimensions or its positioning. The profession recommends using calibrated probes (at least once a year), with a maximum dispersion of ± 0.25 ° C for temperatures above 100 ° C. Instructs the user to check the location of the real cold spot (and not assumed) and the ability of its instrumentation to make a usable measurement (not so simple!)
Notion of minimum Fo and target Fo:
The minimum Fo is the result of the Fo calculation obtained by combining the various factors unfavorable to the sterilization process, namely:
• conditions for filling the product in the packaging: temperature, weight, pressure, gas volume
• loading conditions: compacted layers, cold spot of the autoclave
• autoclaving conditions: critical load, critical maintenance of the retort and critical operation of the workshop capacity
The minimum Fo thus calculated must satisfy the level of destruction required, also called target Fo. Thus, the stability of the product is guaranteed and responds to the term "canned food". If the minimum Fo is lower than the target Fo, an increase in treatment time or temperature is usually used to raise it. However, as we often practice at AXITHERM, it is possible to obtain the same result by reducing the dispersions of Fo (= increase value of minimum Fo) by adapting the sterilization schedule. This method called OTTA makes it possible to avoid lengthening cycle time and overcooking strong >.