Here's a photo of three pecans we picked up with the harvester this fall. You might recognize these nuts as being all from the same cultivar--Kanza. The light colored nut on the right is from this year's crop, while the other 2 nuts were left behind from the 2010 crop. One of the things we look to remove from the cleaning table are old nuts that usually appear as dark reddish black nuts (nut pictured in the center). After sitting on the ground an entire year, these nuts become rancid and/or moldy.
We missed the moldy nut on the far left on the cleaning table only to find it later in a batch of cracked nuts. Look at the shell that still remains on the moldy nut. Its darker than the new crop nut but doesn't have that oil soaked appearance of the nut pictured in the middle. With thousands of nuts moving across the cleaning table, it easy to see how we missed pulling the moldy nut (before it was cracked) out of our 2011 crop.
I find it remarkable that pecans missed at harvest can survive an entire year out in the field without being discovered by squirrels, mice, crows, woodpeckers, insects and even deer. However, every year we find just a few old nuts come racing across the cleaning table that need to be thrown in trash pile.