QUESTION:
How do you tell when a green tomato harvested early to prevent freeze damage will ever turn red and ripen?

ANSWER:
This can simply be done with a sharp kitchen knife. Harvest a tomato typical of the majority of green tomatoes on your plants. Look at size but pay particular attention to fruit color – a physiologically mature tomato will change from dark green to very light (white) green. Slice through the center of the tomato. Closely examine the seed within the fruit. If the seeds are covered with a clear gel (placenta tissue) which cause them to move away from the knife, then that size and color fruit are physiologically mature and will eventually turn red (ripen) from the inside next to the seed (mature seed produce ethylene which is a fruit ripening gas). If the seeds are cut by the knife then those fruit will never properly ripen and will probably rot. Compare the color and size of the tested fruit when harvesting tomatoes on your plants. Most similar fruit will eventually ripen and turn red.

Also, cool fall temperatures cause the abscission zone (the area where the tomato is attached to the plant) to weaken, and the heavy fruit subsequently falls. Gather fallen tomatoes as soon as possible, wipe them clean with a 10 percent solution of Clorox and store them in a warm place to ripen. These aborted tomatoes will rot if left on the ground.

You can pick all the physiologically mature tomatoes and place them in a newspaper-lined and covered box in a cool (room temperature) place (NOT THE REFRIGERATOR). Check these tomatoes daily. Though you will lose some, it is probable you will be eating fresh sliced tomatoes for Christmas dinner.