Grains are sold as a bulk commodity. The sale typically takes place at a "grain elevator" where the grain is dumped into a shared storage pool by the truckload.

I'm not sure how anything about brands could apply. Any "brand" ends at the grate where you dump the grain.

Similar with other ag products. Remember how we just had that E. Coli outbreak in lettuce and nobody had any idea for several days where exactly it came from, so they had to broadcast the warning across the entire nation?