I do this every year, you have to par boil them for a few minutes so the skins comes off, put them in ice water to stop cooking, then put them in canning jars with 1 teaspoon of pickling salt, 1 tsp of lemon juice, put new lids and bands, water bath for 20 minutes. takes time but well worth it to have fresh tomatoes in winter. Pm if you have any questions.