Patulin is formed by molds of the species Penicillium, Aspergillus, Byssochlamys and Paecilomyces variotii. In decayed pome patulin is produced by Penicillium expansum, there can be found up to two grams of toxin per kilogram of rotten fruit.

Legal threshold values are regulated differently in each country and are defined e.g as 50 µg/kg for apple juice, as 25 µg/kg for fruit compote, or as 10 µg/kg for maximum occurrence in infant formula.

Chemical formula for Patulin C7H6O4
Molecular Weight: 154,12 g·mol−1