Officials at the Kartellamt in Bonn squeezed €13.2 million ($15.8 million) from two businesses, Böhmer and Kuhn, which collaborated to fix prices for potatoes and onions in their contracts with retail group Metro.
The figures the firms cooked up meant that “price competition between the two main suppliers of the Metro group was effectively eliminated,” competition watchdog chief Andreas Mundt said in a statement.
Authorities only sniffed out the unsavoury scheme when another firm in the sector reported the collusion in exchange for leniency.
Germany's food sector is no stranger to scandal, as sausage makers and brewers alike have suffered fines after being caught collaborating to skim off extra profits in recent years.
Supervisors have also fined truckmakers who hitched their prices together in a cartel of their own.