v> To provide the proper conditions for silage or haylage storage in agriculture it is necessary to regularly  monitor the formation of certain organic acids in it. For example, the formation of butyric acid can indicate  spoiling of material. Formic or propionic acids can be artificially added to increase the nutritional quality.  The same materials and some other biodegradable waists (agricultural residues, sewage sludge, etc.) are  also used in biogas plants, where the fermentation process must be carefully monitored, in particular, by  the determining the certain organic acids.