|I think she means corn that looks like this.|
|Or soybeans that look like this.|
Grain crops like corn, soybeans, wheat, barley, sorghum and others are harvested when ripened and for those plants, ripening means they have dried down and their green tissue has turned brown. Since these crops have a long storage life, they must be low in moisture in order to be held in large grain bins without going moldy. They have to be dry in order to have any shelf life for future use in a food or feed product. Consumers don't want moldy grain in their food, nor do animals care for moldy grain in their feed, not to mention the health risk to both if moldy grain is consumed by either.
In our combine, we have a monitor that tells us how many bushels per acre we are harvesting, how many acres we have harvested, and what the moisture content is of the grain we are harvesting. If we harvest grains that are too high in moisture and deliver them to a grain elevator, we get "docked" or penalized for high moisture content. We try to harvest at the right moisture level but occasionally have to run grain through a grain dryer to lower the moisture before we sell it. Drying grain gets expensive so we do our best to harvest at the right moisture.
Right now, corn is running 14-18% moisture. We get docked if the moisture is over 15.5%. We grow 104 - 112 day corn which means we can stagger our harvest dates over time so that the corn does not ripen all at the same time. This helps us plan the demand on our farm equipment and manage our resources more efficiently.
And so now you know why grain crops turn brown... in case you ever wondered.