I have been ripening some small green tomatoes for a few weeks, in a cupboard under a sheet of paper. Just put them in a plastic bag now. Some are still green and quite hard, the ones which have turned or are turning red seem to be a little softer, in some cases slightly spongy. Am I doing something wrong or should I carry on and hope for the best? The tomatoes are small (about half the size of snooker balls) and were grown in a garden in Northern England.