Most of the growth and mycotoxin production of the storage molds takes place after the harvesting, but the mold comes into contact with plants already in the field or at harvesting.. The most important storage fungi species originate from genuses Aspergillus and Penicillium. The major two species from Aspergillus genus are A. flavus and A. parasiticus. Both can produce AFB1 and AFB2. A. ochraceus, A. westerdijkiae, A. steynii, A. carbonarius and A. niger are also known as storage fundi. They all can produce ochratoxins, but we rarely find them on grains. The only known ochratoxin producing species from Penicillium genus are P. verrucosum and P. nordicum. P. verrucosum is more common from the two and we typically find it on grains. Mycotoxin production isn’t essential. It starts when fungi are in stress. Mycotoxins can harm human and animal health. Some of them are cancerogenic. The most important mycotoxins found on grains and grain products are aflatoxins and ochratoxins. The major strategy for reducing fungal growth and mycotoxin production is providing adequate storage facilities. Controlling temperature and humidity is necessary. An useful measure for providing pristine food and feed is rinsing the grains surface and sorting foreign particles, moldy or damaged grains from healthy looking grain mass.