Today we pressure canned 20 pounds of freshly picked San Marzano tomatoes. These are wonderful tomatoes for canning as they peel easily and contain far less seeds than most other varietals.
20 pounds of tomatoes yielded 8 quart jars, with no added liquid.
I process them in what I call ‘semi-crushed’ form. After peeling and slicing them I crush them lightly to release enough juice for the canning process, while still leaving many large chunks. They are the perfect consistency for using in soups, sauces or chili and will break down quickly when cooked.
These are peeled by briefly blanching and moving to an ice bath, after which the peelings can be rubbed off quickly.
They are brought to a boil for 5 minutes, and added to quart jars which contain 2 tablespoons of lemon juice, then put into the All American canner for 15 minutes at 10 pounds of pressure.
You can look up the cooking time details here.
You might be asking why acid must be added to canned tomatoes if you are using a pressure canner. The answer is simple – You can cook them without adding acid if you want to do a standard low-acid vegetable canning cook time of 40 minutes. This long cook time would destroy the texture and nutrient value of your tomatoes though, which is why most recipes you’ll see choose to compromise a shorter cook time with the addition of acid.