For companies in the food sector, checking the correct temperature all along the cold chain is one of the basic measures for assuring quality and guaranteeing compliance with legal and internal standards. Because temperature fluctuations are often the cause of spoiling or impaired quality when it comes to food.
Temperature measurements
for an uninterrupted cold chain
For companies in the food sector, checking the correct temperature all along the cold chain is one of the basic measures for assuring quality and guaranteeing compliance with legal and internal standards. Because temperature fluctuations are often the cause of spoiling or impaired quality when it comes to food.
In the case of foods which cannot be stored at room temperature without potential problems, the cold chain must not be interrupted. Most products pass through many different hands on their way to the end consumer – in transport, temporary storage facilities and distribution centres. When products are handed over to another logistics service provider or to a distribution centre, the responsibility for food quality and food safety also changes again and again all along the cold chain. Failure to comply with the cold chain can lead to damage to corporate image and thus losses in turnover for the company. Temperature control therefore serves to ensure the safety and marketability of foods which are subject to the cold chain. In addition to the legal requirements and temperature limit values which are binding during the production, transport, storage and sale of foods, various temperature terms are used: storage temperature, product temperature, air temperature, core temperature and surface temperature.
What are the differences between these types of temperatures and how significant are they in terms of product quality? Furthermore: what measurement methods are there and which of them are best suited for monitoring food temperature?
We would like to examine and clarify these questions in greater detail below.
Measuring in rooms:
the challenge of stratification
| Measurements taken inside a room may be distorted by what is known as stratification around surfaces. The risk of stratification arises if the surface temperature differs a great deal from the air temperature.
To avoid measurement errors of this kind, a minimum distance from surfaces should be adhered to. This minimum distance has been reached when no further changes in the readings occur in spite of the distance being altered. The measuring location for every measurement should therefore be chosen with care and an appropriate measuring distance adhered to. This also applies to conditioned air inlets from heating or refrigerating equipment. This kind of stratification can also occur in static air between the floor and ceiling, for example in big store rooms. Control measurements should therefore be taken at the points which have been found to be representative from a survey of the indoor climate. |
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Humidity and temperature behaviour on surfaces. |
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Air and product temperature:
what really is the difference?
In terms of temperature control, a distinction needs to be made between the following types of temperature: the air temperature indicates how cold the air in the refrigeration facility is. The temperature of the cold air enables us to conclude that the refrigeration facility is achieving the correct cooling capacity. However, the air temperature which is determined cannot be equated with the so-called product temperature. The product temperature is predominantly determined by the air temperature.
However, the reaction to fluctuations in the air temperature is dependent on the type of food or packaging or on the condition or degree of processing (pre-cooked, raw, frozen) of the food. The product temperature of a completely frozen chicken is relatively constant, even when there are considerable fluctuations in the air temperature, whereas the temperature of 100 g of fresh minced meat adjusts significantly more quickly to the change in air temperature. This means that the actual product temperature may differ from the air temperature within the refrigeration facility.
Negative influencing factors (e.g. the radiant heat of the refrigeration unit, frequent door opening or loading errors) cause increased cold air temperatures, often not noticed by staff. Temperature probes and displays permanently installed by the manufacturer of the refrigeration unit can nevertheless indicate air temperatures within the specified limit values, because the temperature probes are placed in the air outlet area (that is in the cold areas of the refrigeration facility). This means it is particularly important to take the different temperature zones within a refrigeration facility into account when measuring. If this is not done, the air temperature measured and documented by the installed probes is not really correct.
The product temperature is the temperature of the product and can be determined either as a surface or core temperature. It is measured on the surface (surface temperature) or in the core (core temperature) of the food. The product temperature is a crucial factor in terms of compliance with product-specific characteristics through to the expiry of the best before or use by dates.
Two measuring methods:
Spot check or recording
In terms of temperature control, we differentiate between two types of monitoring:
Spot check measurementIs carried out with portable (mobile) temperature measuring instruments, which are either pure measuring instruments (which merely display the measurement value), or storage thermometers which save the measured data in an internal memory or send them to a data store wirelessly. |
Continuous data recordingThis involves a measuring instrument with a memory remaining with the goods (or in their proximity, e.g. the refrigerated room) and recording and storing values at regular intervals (measuring intervals). Depending on the type of data logger, the data are either stored in an internal memory and read out manually (offline data logger) or sent to a data store wirelessly (WLAN data logger). |
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Portable measuring instruments:
which one meets your needs?
Portable temperature measuring instruments are available in various designs and with different probes.
Instruments with a
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Instruments with a
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Instruments with
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Non-contact measurement:
what do I need to keep in mind?
There are instruments which measure the temperature without direct contact with the food: infrared measuring instruments. They are suitable for obtaining a rapid overview of the temperature of the products.
This so-called non-destructive measurement enables the temperature to be determined without the instrument coming into contact with the product.
The measuring instrument:Measure with a clean lens. Acclimatize the measuring instrument to the ambient temperature. |
The measurement surface:Measure clean surfaces. Measure packaged foods at points where the product and the packaging are in direct contact. |
The measuring distanceThe closer the better. |
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Ideal for continuous recording of measuring values:
mobile or stationary data loggers.
Data loggers are instruments for continuous data recording which store measured data in an internal memory or send them wirelessly to a storage unit.
Mobile data loggers• Mobile data loggers for accompanying goods: measurement in the products’ immediate vicinity • No direct contact with the goods: placement of the data logger for example in the package or between Important: data loggers for refrigerated and deep-frozen foods must comply with the EN 12830 standard in the EU. |
Stationary data loggers• Stationary data loggers: placement for example in the refrigerated area of a vehicle, in a transport box or in the storage room |
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When using handheld measuring instruments:
how do I measure correctly?
The most accurate measurement is always a core temperature measurement, i.e. a penetration probe measures the temperature in the interior of the refrigerated goods. However, this means damaging the packaging for many products. In order to avoid this, a three-stage process has been established in practice:
1. Firstly, the surface, for instance of yoghurt pots, is scanned using an infrared measuring instrument to get a quick overview of the temperature of the products. If the temperature is clearly within the “green range”, the test is finished. Example: the yoghurt pots have a temperature of +5°C (target: max. +8°C).
2. Is the temperature of some yoghurt pots over +8°C? Then a contact probe is inserted between two yoghurt pots and a measurement taken. This measurement also enables non-destructive temperature checking.
3. Is the temperature still too high? Then a penetration measurement is finally carried out on one or more pots. The probe is inserted through the lid into the foodstuff and thus measures the correct core temperature.
In order to carry out this three-stage process quickly with one temperature measuring instrument, it is best to use a combination instrument that has both an infrared and a penetration probe, e.g. the testo 104-IR. You will find more information about this at:
https://www.testo.com/en-ZA/testo-104-ir/p/0560-1040
What else you should keep in mind for measuring instruments |
Measuring instruments which are used to determine the temperature of foods must be calibrated regularly. A recalibration is recommended when there are larger discrepancies. Calibration means comparing the measuring instrument with a reference instrument which is traceable to a national standard. There are special service providers for this, such as Testo South Africa. You can find out more at:
https://www.testo.com/en-ZA/services/calibrations
In addition to the directives and regulations for food producers, suppliers and retailers, there are also stipulations for measuring instrument manufacturers which precisely regulate the technical characteristics or minimum requirements for measuring instruments and data loggers. This is necessary in order to achieve standardized regulations regarding discrepancies in measurements, recording periods, protection against dirt and water, etc. Users should make sure that their instruments comply with the relevant standards (e.g. DIN EN 12830, EN ISO 13485, DIN EN 13486) and that what is known as a type test (approval) has been carried out by the manufacturer.
When using data loggers:
what is it best to measure and where?
(Deep) FreezersIt is above all the air temperature which is checked in freezers and deep freezers. If these are controlled using spot check measurement, this should be determined using a suitable air probe, preferably in the vicinity of the air recirculation. This is where the air is warmest in the (deep) freezer. If the appropriate temperature is measured here, the freezer can be assumed to be working properly. In order to check whether the cooling capacity is sufficient and to ensure the correct product temperature, a further check of the surface temperature of the refrigerated goods is recommended using an infrared thermometer. The use of data loggers with several input channels is recommended for the long-term temperature monitoring of (deep) freezers: one probe measures the air temperature at ground level, another at the maximum load line and a third at the air recirculation. |
Refrigerated or deep freeze roomsLong-term temperature monitoring is obligatory for all refrigerated and deep-freeze storage areas which are larger than 10 m3. A data logger can be used for this. A suitable measuring interval is 15 minutes (e.g. according to EN 12830). The optimum temperature range for the relevant area can be monitored by means of limit values. Depending on the design of the data logger, the stored temperature data can then be read out either manually or automatically. WiFi data loggers minimize the manual effort involved in temperature monitoring. These automatically send the measured data to a data store where they can then be easily accessed via PC, tablet and smartphone. Where there are violations of limit values, there is also an alarm notification to enable corrective action to be taken as quickly as possible. Temperature mapping is recommended to ensure optimum placement of the data loggers at the critical points of the refrigerated rooms and store rooms. There are special service providers for this as well. |
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For more information contact:
Testo South Africa (Pty) Ltd
1 Glen Eagles Office Park
Cnr. Braambos & Monument Rd.
Glen Marais 1619
Kempton Park, South Africa
Contact number : +27 11 380 8060
Email : info@testo.co.za
