An Ode to Odour: DEKRA Offers Odour Measurements Across Germany
Jul 20, 2026CorporateStephan Mahlberg, Technical Manager of the Air Quality Monitoring Station at DEKRA and his team measure odors from industry, commerce and agriculture across Germany – from coffee roasters to sewage treatment works and composting plants. We accompanied the odor assessors in green on an on-site assignment.
Odour Nuisance Has Many Causes
It takes more than just a wrinkled nose to get DEKRA’s odour assessors out on a call. In most cases, the request comes directly from the plant operator. The reasons for this include regulatory conditions imposed by the authorities, mandated inspections, acceptance tests or an increase in complaints from neighbors. “However, it also happens that, for example, restaurant owners proactively approach our air quality monitoring center to avoid conflicts over odour nuisance,” explains Mahlberg on his way to his next assignment. The DEKRA team was commissioned to determine the odour levels at a composting plant near Stuttgart.
From Enquiry to Objective – The Range of Odour Measurements Is Diverse
The procedure for odour measurements varies depending on the location, type of facility and objective. If the facility is unfamiliar, a site inspection is carried out before sampling: How many measurement points are required? How can the measurement points be accessed? And what is the facility’s typical operating capacity?
Parameters of this kind form – as is the case with today’s operation – the basis for a specific measurement plan. Composting plants are a classic application for DEKRA’s odour assessors: here, a limit of 500 European odour units per cubic meter (ouE/m³) is often set as emission limit value at the biofilter – an open filter bed made of wood chips, in which micro-organisms purify the exhaust air flowing through it. “The higher the units, the more intensely we generally perceive odours,” explains Mahlberg. By now, a resinous, organic scent tells us that we are getting closer to our destination.
Biofilters in Focus – How Odour Measurements Work in Composting Plants
“In summery temperatures like today’s, we particularly enjoy working outdoors,” says Mahlberg as we carry the equipment from the car to the measuring point. For the measurement itself, however, the weather is of secondary importance: the odour assessors record the exhaust air conditions at the biofilter and the weather conditions accurately so that the measurement can be better understood later. It is crucial that the plant is operating under typical operating conditions. “Only when that is the case does the sampling begin,” adds his colleague Beate Kyriazis, deputy technical manager for the air quality monitoring station at DEKRA. The biofilter is quickly located, and the work steps are perfectly synchronized: DEKRA’s odour assessors divide the layer of wood chips into several grid sections so that they can examine the biofilter thoroughly.
Next, the one-square-meter sampling hood is brought into use. This tapers upwards in a funnel shape and is fitted with a small exhaust flue and an opening for sample collection. The team on site places the hood over the wood chip bed and measures the airflow velocity through the hood at various points on the biofilter‘s surface. “This allows us to determine whether the biofilter in the relevant section is actually well ventilated,” says the odour expert. The assessors then connect the exhaust chimney to a PTFE hose, which in turn leads to the sampler containing the prepared sample bag. As soon as the pump starts, a vacuum is created in the tube and the bag slowly fills with air.
Nationwide Odour Measurement: Six Hours Between Sampling and Analysis
A single sampling takes half an hour. The DEKRA team moves the hood at a steady pace across several fields on the biofilter until a mixed sample is obtained. Finally, the filled sample bag is sealed, labelled and stored away in a light-protected location. The team repeats this procedure three times in the cleaned exhaust air, where the cleaned air emerges from the biofilter. At the same time, three samples are taken from the raw gas – directly in the duct upstream of the biofilter. The six samples in total form the basis for the subsequent odour assessment.
Due to its geographical proximity, this assessment is currently carried out at a DEKRA laboratory in Stuttgart. DEKRA also operates an odour laboratory in Braunschweig, which is particularly well-suited for sampling in central and northern Germany.
It is crucial that no more than six hours elapse before our test manager and members of the odour panel evaluate the samples in an odour-neutral, well-ventilated room.
Beate Kyriazis, Deputy Technical Manager of the Air Quality Monitoring Station at DEKRA
The Olfactometer and its Role in Odour Measurements
The olfactometer – an unassuming, box-shaped device – distributes the sample air to the respective test stations. To determine a meaningful average value, four panellists are always present for each odour assessment. Before the odour measurement, they assess the reference substance n-butanol, to ensure that their sense of smell falls within the normal sensitivity range. But be warned: anyone who reacts too sensitively or insensitively is not suitable for the test series.
During the actual measurement – olfactometry – the olfactometer mixes the air from the sample bags with purified, odourless air and presents it to the panel in gradually increasing dilution levels. To an outsider, this looks rather unspectacular: the panellists sit in front of small sniffing ports and inhale on a signal. As soon as they detect an odour, they press a button.
For DEKRA, the assignment concludes with comprehensive documentation and a detailed report. “Ultimately, it is the relevant regulatory authority that decides how the results of measurements ordered by the authorities are to be assessed,” explains Mahlberg. After a day’s work filled with strong odours, he is particularly looking forward to the familiar scent of his own home.
As an accredited measurement body, DEKRA is a comprehensive partner for air quality measurements in industry, commerce and local authorities. In addition to olfactometry, DEKRA offers immission and emission measurements, as well as functional testing and calibration of measurement and monitoring equipment. In addition, DEKRA carries out immission forecasts and dispersion calculations, determines chimney heights and provides real-time air quality monitoring. In this way, DEKRA supports operators and authorities in complying with legal requirements and reliably assessing air-related risks.