What We Do

The Odour Threshold Shop (OTV) aims to make standardised reproducible odour threshold values available to the odour research and Fragrance & Flavour community.

It offers the usual Odour Threshold Value (OTV) from literature but also high-quality OTV’s measured according to standard EN13725, traceable to the European Odour Mass (EROM).


There are different qualities:

AAA  Measured according to European standard EN13725:V2

  AA Measured according to European standard EN13725:2003

    A Literature value compared to EN13725 outcomes for n-butanol and at least five additional odorants

    B Literature value compared to the EROM value for n-butanol according to EN13725

    C Legacy literature value without any traceability to standardised units

If you need an OTV for something important, insist on AA or AAA.

The OTV values can be available for free and the shop also allows you to have an OTV value measured for a reasonable cost through crowdsourcing or measured exclusively for you, ASAP, at full cost, if you are in a hurry.

Quality of OTV: A history

The measurement of odour thresholds goes back a long time. The first OTV value was published by Zwaardemaker in 1895.

In the 20th century, many researchers published OTV’s. A very complete compilation of values was prepared by Van Gemert. See our compilations page for more.

From this compilation we can see that the values vary over a wide range, depending on the method used, the panel members used, the measuring room etc. Researchers typically did their own thing, and the OTV was defined by the average of the panel used (which was then extrapolated, boldly, to ‘the population).

In the 1980’s a radical change in the definition of the OTV happened, in the NVN2820 standard method for olfactometry, published in the Netherlands. This standard aimed to make olfactometry more reproducible for application in environmental odour regulation compliance. It defined the Dutch odour unit (geureenheid) as equivalent to the olfactory stimulus of 20 ppb/v of n-butanol in neutral odourless gas.

In the subsequent European standard EN13725:2003 this approach was adopted but with a different agreed reference value of 40 ppb/v. The reference for the European odour unit was defined as the European Reference Odour Mass:

European Reference Odour Mass , erom

conventional quantity value [11] for the European odour unit, equal to a defined mass of a certified reference material. One erom is equivalent to 123 mg n‑butanol (CAS‑Nr. 71‑36‑3). Evaporated in 1 cubic metre of neutral gas this produces a concentration of 0,040 mmol/mol


In the revision of the EN13725, ongoing, a procedure for measuring the EROM for substances other than n-butanol was included.

So, in the history of the OTV there is a before and an after the definition of the odour unit. Before it was the mean value of a sample from a population (often a very small sample!). After is is a well defined unit, the ouE·m-3, traceable to the unit mass.

The result is a convergence of the values. The OTV can now be measured with a known uncertainty.

The Sensenet OTV shop aims to make more traceable OTV values available to the odour professional.

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