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Infosite for the treatment of food

Smoking and cooking of food is a necessary part of the processing. Why, how does this work best and what are the underlying calculations? Here we explain what C and F values mean, how cooking has changed over the years and how we are developing it further.

Why are meat and sausages cooked?

Meat and sausage products are primarily cooked so that they have a longer shelf life. Small quantities can be treated in boiling kettles, i.e. hot water. For large quantities, cooking chambers with saturated steam are usually used. Trolleys specially manufactured for this purpose are filled with the products and pushed into the cooking chamber. The door is closed and a program is started.

However, the quality of the products can be affected in various ways. A product can become too hot or the products are too long inside because the contact thermometer does not function reliably. This can also happen with mobile cooking chambers – but the effects are greater there because more products are treated.

Over the decades, controls improved with reliable watches and better temperature controls. Recently, more and more attention has been paid to precise control of the core temperature. Unnecessary cooking leads to high weight losses and a perfect core temperature significantly improves durability. For this reason, core temperature rules attempt to achieve the shortest cooking time with the lowest prescribed core temperature. This ensures optimum shelf life.

How the cooking process determines shelf life

In the manufacture of preserved foods, the use of high temperatures reduces the number of microorganisms responsible for the spoilage of the product.

Because of this method of preservation, it is also known that it is not only the height of the temperature that is important. It is much more important to know how long a temperature has an effect on the product. The efficiency of these two influences, the level of the temperature and the exposure time, are expressed in the so-called F value.

The importance of this value has been recognised in the sterilisation of canned food. Modern production methods cannot be imagined without the F-value. The same applies to the normal cooking process, which takes place below 95 degrees Celsius. However, this is pasteurisation: the microorganisms to be killed are not spores, but D-streptococci. These are the most resistant in this temperature range.

Research work in this field of pasteurisation makes it possible to use the correct F-value here as well and to cook for a correspondingly long time on the basis of experience.

F-Value...

… is composed of a ratio of two numbers: On the one hand, the height of the temperature in the chamber. On the other hand, the duration (time) of exposure to the product of this temperature.

(F = D (\log N_0 – \log N))

What happens with the F-value?

The microorganisms on which the calculations are based, in particular the D-Streptococci, are killed from a temperature of 55 degrees Celsius. This means that the total number of germs is reduced from a temperature above 55 degrees Celsius. Depending on the level of this temperature achieved, a corresponding F value is achieved per unit of time of one minute. The following values are important for the F-value of pasteurisation:

Anfangsmesswert55 Grad Celsius
Bezugstemperatur70 Grad Celsius
Wert1 (Wert für die Zeit-Temperatur-Abhängigkeit der Keimabtötung)

With this basis and the formulas generally known for calculation (F = D (\log N_0 – \log N)), the F values listed below are used to determine the total value.

Grad CelsiusF-WertGrad CelsiusF-Wert
550,032763,981
560,040775,012
570,050786,310
580,063797,943
590,0798010,000
600,1008112,589
610,1298215,849
620,1588319,953
630,2008425,119
640,2518531,623
650,3168639,811
660,3988750,119
670,5018863,096
680,6318979,433
690,79490100,000
701,00091125,893
711,59092158,489
721,58593199,526
731,99594251,189
742,51295316,228
753,163

We therefore find that with every temperature increase of 10 degrees Celsius, the corresponding F-value also increases tenfold. The relationship between temperature and time is also evident. For example, if a product had a temperature of 63 degrees Celsius for five minutes, this would give an F-value of 1,000. A temperature of 70 degrees Celsius needs only one minute for the same F-value.

What is the final F-value to be achieved by the cooking process?

A recommendation about the F-value to be achieved indicates that it should be 40.
This recommendation is based on the following values:

beginning bacteria count before cooking:10E7 total bacteria per gram

End bacterial count after cooking:10E-3 Total bacteria per gram

In practice, this reduction in the germ count means that 99 out of 100 products are germ-free and that one piece still has one germ.

How to calculate the F-value

Two methods allow you to obtain an end F value. The first option requires that the core temperature be plotted as a curve using a temperature recorder. This curve is subdivided into minute intervals in the range above 55 degrees Celsius. The entire temperature curve, which is over 55 degrees, is decisive. This also includes the time until the temperature falls below 55 degrees again when cooling down. Each time period is now assigned the F-value corresponding to the temperature value and added continuously. The addition results in the final F-value. This method is only used if you want to check a cooking process in its sequence.

A second possibility arises with the use of microprocessors. These devices register the temperature curve via a core temperature sensor during the cooking process and independently calculate the achieved F-value. In addition, with these controls it is also possible to control a final F-value and abort the cooking process on the basis of this criterion. This type of F-value cooking is standard with our controllers.

Why by F-value and not by core temperature?

Since the cooking according to the core temperature is already known and it seems much more complicated to record the F-value, this question is understandable.

In our opinion, the determination of a certain final core temperature value, as is done in many places today, does not make sense throughout. Due to the wide range of products, the different calibres, the different product dimensions, the varying product weights and not least the different thermal conductivity values, the same core temperatures produce different results with regard to shelf life and the killing of microorganisms.

With the experience of canning it is obvious that the F-value is the decisive factor. The problem is that different final core temperature values would have to be used for each calibre, each dimension, each weight, etc. in order to achieve the same F-values. This is almost impossible even with today’s controls.

The C-Value...

… describes the surface boiling damage of a product. If the temperature at the surface of a product is higher than the core temperature, this has a negative effect on the natural quality such as jelly heel or vitamin degradation. This C-value is calculated on the basis of a temperature curve.

Why do people talk more and more about cooking damage during the cooking process?

The increase in core temperature is much slower compared to room temperature. This can be explained by the different thermal conductivity values of the room air and the product. It is therefore rather suboptimal to run a cooking process with a single temperature value for the room temperature if the core temperature shows a very slow increase.

In other words, it has disadvantages if an ambient temperature of 75 degrees is maintained at an initial core temperature of 12 degrees Celsius, if no drastically faster increase in the core temperature is achieved than with clearly lower values. On the one hand, this is energy-technically inefficient, and the harmful influence of the high ambient temperatures on the food to be cooked can be just as problematic. These influences affect, among other things, the natural quality, such as jelly sales or vitamin degradation. These effects, summarized under the term “cooking damage”, are expressed in a specially created comparative value, the C value.

This C-value is also calculated based on a temperature curve. The room temperature is used for this purpose. The calculation is done analogously to the F-value, also from and up to 55 degrees Celsius, but with other individual values, as shown in the table below.

Each time after this temperature has been reached, a corresponding C value is obtained per unit time of one minute. The C value for the cooking damage is based on the following values:

Anfangsmesswert55 Grad Celsius
Bezugstemperatur100 Grad Celsius
Wert38 (Wert für die Zeit-Temperatur-Abhängigkeit der Garung)

Grad CelsiusC-WertGrad CelsiusC-Wert
550,065810,316
560,070820,335
570,074830,357
580,078840,379
590,083850,403
600,089860,428
610,094870,455
620,100880,483
630,106890,513
640,113900,546
650,120910,580
660,127920,616
670,135930,654
680,144940,695
690,153950,739
700,162960,785
710,173970,834
720,183980,886
730,195990,941
740,2071001,000
750,220
760,234
770,248
780,264
790,280
800,298

The C values, unlike the F values, only increase tenfold every 38 degrees.

Ebenso, the table shows that it is not ideal to work with unnecessarily high temperatures with regard to cooking damage. If we assume, for example, that a product is to be brought to 65 degrees Celsius and this is achieved in 10 hours, whether we work at 78 degrees or 70 degrees room temperature, the following two C-values result:

in comparison

At 10 hours with 70 degrees Celsius = 600 x 0,162 = C 97,2

At 10 hours with 78 degrees Celsius = 600 x 0,264 = C 158,4

Which final C-value is the best?

The optimal C-value cannot be quantified directly like the F-value. Rather, the cooking process should be designed so that the C-value is as low as possible. Based on the various considerations, it can be stated that a cooking process fulfils the following criteria:

Erreichen eines idealen End-F-Wertes
Energietechnisch muss die Raumtemperatur laufend auf die absolut minimal notwendige Höhe angepasst werden.
Mit einem möglichst tiefen C-Wert Kochschädigungen vermeiden.

Why optimize cooking?

Optimized cooking means, during the available time, using as little energy as possible with a low chamber temperature to achieve the lowest possible C-value and an optimal F-value. Under these conditions, unnecessary weight loss, surface damage, protein leakage and bacteriological cooking are avoided.

How it started

A first step, and thus an essential beginning, is that cooking processes are either monitored with a recording device or directly via an appropriately equipped computer control system. If a recording device is available, it is possible to record the temperature curves for the core temperature and the room temperature and thus draw conclusions about the currently achieved F and C values. The step cooking program already brings some good success with regard to the C-values.

Stufenkochprozess Grafik klassisch alte Art zum Kochen

Delta-Cooking

This is the further development of the step cooking program. “Delta” stands for difference and “T” for temperature. This means that a cooking program is carried out with a temperature difference. But which temperature difference is meant? We speak of the difference between the core temperature and the treatment temperature (chamber temperature). However, there is no agreement among experts on the size of the difference. For good reason. Here again the criteria already mentioned such as product dimensions, calibre and thermal conductivity play an important role. Some prefer a Delta-T of 15 degrees Celsius, others of 20 degrees or 25 degrees. Therefore, a Delta cooking program is only good if this Delta-T can be set differently from program to program, i.e. arbitrarily.

The sequence of a Delta-T cooking program is simple for most variants:

– A batch of ham should be cooked to a core temperature of 68 degrees Celsius. A cooking program with a Delta-T of 25 degrees Celsius is available. The maximum upper treatment temperature is 75 degrees Celsius. The initial core temperature is 12 degrees Celsius.
– After starting this program, the controller will maintain the treatment temperature in the plant at a constant 25 degrees above the measured core temperature. At the beginning a room temperature of 37 degrees is required. The Delta-T of 25 degrees is no longer maintained from the time when the core temperature plus 25 degrees results in more than 75 degrees. From this point on, the maximum treatment temperature is 75 degrees.
– This type of delta cooking brings a noticeable improvement in terms of cooking damage and energy consumption compared with normal stationary cooking or step cooking programs.

The problem of Delta-T cooking: Depending on the product, product dimensions, caliber and thermal conductivity value, the cooking process takes different lengths of time. This time span cannot be determined with these simple programs. The expected F-value is also not known because the core temperature is uncontrolled.

Delta-T Kochen normale Art zu kochen Produkt

E&B cooking comes after Delta cooking

Here comes the innovation from E&B smoking technologies: It is based on Delta-T cooking, but thinks ahead. In order to control the course of the core temperature curve as accurately as possible, the Delta cooking program must have a different structure. In the programming, the program requires three criteria with which the computer can intervene in the process at any time. For this purpose, an initial and a target value are required for the treatment and core temperature, and the process duration is also specified. The computer uses this data to calculate the desired program sequence. Based on the initial values, the Delta-T is determined for the respective program, i.e. always exactly as large as the user needs. The target values are used to calculate the rectilinear temperature curve for the target value of the core temperature and the parallel room temperature, which only serves as a maximum limitation.

We call this Dynamic Differential Temperature Cooking.

When this program is running, the control system configures the cooking process so that the actual value of the core temperature is as close as possible to the calculated setpoint. This means that the heating is only used if this is necessary due to a too low core temperature. Since the core temperature rise is known to be very slow, the heating power is used in the delta cooking phase in a clocked manner in order to really consume just as much energy as is necessary.

As this program calculates and also controls a straight line for the course of the core temperature from the start value to the target value, an expected F value can already be calculated during creation. This provides the user with a very high level of production reliability and consistency in quality. Compared to step cooking or Delta-T cooking, it is possible to have lower energy consumption and less weight loss.

EB Kochen dynamisches Differenztemperaturkochen Grafik

Conclusion

Finally, it can be safely said that the supposedly very simple cooking process holds a great variety of interesting aspects. Rethinking your own product range is worthwhile in any case, as there are optimization possibilities in practically every business which, it should be noted, improve the ever smaller margins.