Fall is the season for lovely squash, crisp greens, beautiful red tomatoes... and sometimes beautiful green ones, too. As we get closer to frost we often find ourselves in possession of tomatoes that just didn't have enough time to ripen on the vine.
Tomatoes that have started to ripen - that are showing a blush of red or yellow - will finish ripening easily if placed on the windowsill. However, tomatoes that are still completely green will not ripen that way.
The best trick I know of is to place the green tomatoes in a paper bag with a ripe apple (a ripe banana will work, too). The fruit releases ethylene, which helps the green tomato to ripen quickly. Green tomatoes left out, or put in a bag without an apple, run the risk of rotting before they can ripen.
Of course, as Maryann (one of CSA shareholders) pointed out to me, there's nothing wrong with a batch of fried green tomatoes!