I would think you could tell just by feeling of them if not by color...

I bought a plant at a church sale this spring. It is producing some nice fruit, some seem larger than a baseball, not perfectly round but still green. I am watching them and will check again tomorrow but so far this plant looks good, leaves are good and green.

I believe the person said it was a purple russian variety.

What would be the best way to harvest some seeds from this fruit? Pick one fruit and let it overripen? Or take any seeds from any fruit and just dry them and store them soon after cleaning and drying? I'm thinking small envelopes in jars in the back of my fridge for my tomato seeds.

I have sown tomato seed saved from lidl variety pack from 3 years ago. Because of covid-19 and not likely to travel as I normally do, I grow them. I have got an interesting crop from the 12 plants that grew. Yellow plum and cherry. Red plum and cherry and also black plum, which I wonder when are they ripe. I have always thought that when the calix breaks away that they are ripe. I live in W Yorks, so I grow them in the greenhouse. I have been growing tomatoes on and off for 40 years. I don't know the name of Lidl tomatoes but they are different to anything that I have grown before. Stuart Hand