Unless we’re talking about certain cheeses, mold on a food item is a pretty foolproof way to tell it’s gone bad. And since mold is sometimes green or greenish blue—on bread, for example—it makes sense that you’d jump to the conclusion that green grains in a bag of uncooked brown rice are fungal in nature.
But don’t trash the bag just yet. On their FAQ pages, Mahatma and Carolina rice brands both identify those questionable green grains as “immature kernels of rice, [which] have the same nutritional value as mature grains.” The culprit behind the color is the same one that makes unripe bananas green, unripe tomatoes green, and all manner of other plants green: chlorophyll.
According to Seattle-based food cooperative PCC Community Markets, the green grains have probably been harvested from the bottom of the stalk, since those take longer to mature. And you should actually want some green grains in your brown rice, because they’re a sign that manufacturers haven’t tampered with the rice to make it more homogeneous in color.
So if green kernels can’t alert you to brown rice gone bad, what can? In short, all the normal indicators of spoilage: a foul odor, a slimy film, insects, or mold spots. Mold grows when moisture seeps in, so store your rice in a dry, sealed container to prevent that from happening.