Place all the tomatoes you want to ripen in a paper bag. Seal the bag from the top and make several, small holes in them. This will keep some of the ethylene gas that tomatoes naturally produce and help the tomatoes to ripen faster. Keep checking the tomatoes every day and when they start becoming redder, check them every few hours as fruits become overripe very easily. Tomatoes normally take from 1 to 5 days to become fully ripe.