A good method for ripening tomatoes indoors is wrapping them in newspaper. First, separate completely green tomatoes from partially colored tomatoes. Individually wrap each tomato in newspaper, keeping the color groups separate. Check the partially colored tomatoes every day, and the green ones once or twice a week.
When a green tomato shows some color, transfer it to the other group. In this way, tomatoes ripen steadily over a longer time period.
Another method to ripen tomatoes indoors is to place fruits in a paper bag. Close the bag so bugs can not get inside. A simple trick to hasten the ripening process is to add to the bag a fruit that is already ripe. Place green tomatoes on the counter next to a ripe apple or banana. This speeds the ripening process as well.
Place the tomatoes gently in a cardboard box, layering no more than two deep. Cover the box. Check fruits every day for ripeness.
The ripening process can be sped up by altering the indoor temperature. The warmer the temperature is, the faster the tomato fruits ripen. If the temperature is too low, the tomatoes either lose most of their flavor or do not ripen at all.