Creating a rancidity index table and assigning a rancidity index value to an absorption or reflection spectrum of oilseeds, nuts and seeds (2) comprises: – irradiating a sample of an oilseed, nut or a seed (2) with a light source (3), – projecting the reflected and/or transmitted light onto a photosensor (4), – capturing the absorption or reflection spectrum by the photosensor (4), – extracting contents of the sample by determining volatile compounds, – separating volatile components of the sample by means of gas chromatography, – identifying separated volatile components by mass-spectroscopic detection of relevant constituents, – determining a rancidity index value of the sample from identified volatile components of the sample, – assigning the captured absorption or reflection spectrum of the sample to the rancidity index value, – repeating the preceding steps for a representative number of samples and forming a rancidity table from the established rancidity index values and associated abs
