Many food products made from transgenic plants undergo processing steps that make it difficult to test for GM content. Refined plant oils and soy derivates like lecithin are subjected to extreme temperatures and pressures during processing, which destroy most of the DNA needed for detection.
In years past, GMOs in the EU were governed by the novel food regulation, which set out evidence-based labelling guidelines. If no GMOs could be detected in the product, it did not legally require labelling. A new regulation (1830/2003) on the labelling and traceability of GMOs has now shifted labelling requirements to a process oriented basis. This means that products derived from GMOs must be labelled, regardless of whether or not there are GMOs detectable in the final product.
Research projects are looking for the best ways to obtain and share information on GM status along the supply chain from farmers to retailers. If implemented effectively, documentation could replace GMO testing as the main approach to monitoring GMO status, whereas analytical tests, which are relatively expensive and tedious, could be reserved for enforcement purposes.