Tomatoes are super easy to can. Let's review picking, storing, and general info first.
Green tomatoes must be picked after they have turned light green. the dark green ones are too unripe to use or store. (Even my chickens won't eat them which is a red flag.) They are most often made into chutney or pickles, but you could just can them first if you didnt have time, and do recipes later. Or just make green tomato sauce to use instead of the salsa verde that uses tomatillos. I would watch for allergies, stomach upset, or joint pain when using large amounts of green tomatoes. They are in the nightshade family and the green fruits may have more of the chemical constituents that make some other nightshades so sinister, like the poison that accumulates in potatoes that are allowed to get green. Obviously, normal use in meals is fine.
Tomatoes keep quite a while when picked green. They should be spread out in a coolish place (I use the floor under the kitchen table.) A single layer is best, because you can see them all. Next best is in layers with those purple cardboard wavy-contoured sheets they use between layers in bushel boxes of apples. Most grocery store produce folks will give them to you if you come on the day they unpack. Anyway, green tomatoes and all tomatoes that you want to store more than an hour or two, should be set down with the bottom up. The shoulders of the fruit are stronger, firmer, and support weight better than the soft "belly" on the underside. After awhile, the weight of the fruit will cause them to crack and ooze if they are on sitting on their bottoms instead of their shoulders. Many tomatoes will ripen all the way to red when stored this way. Green or ripe tomatoes can be preserved by canning, but avoid overripe ones, which have started to lose the acid that helps preserve them, and have more susceptibility to mold. Use overripe ones fresh in pasta or similar, or process them to a puree and add a good dollop of acid like lemon juice. More about this later.
You want the skin off. Once the tomato is cooked, as it will be in the canning process, the skin will separate and stay firm, somewhat like a shred of plastic bag in your nice succulent tomatoes. So you need to get rid of it. Most people do that with a pot of boiling water. Those blanchers made of speckled enamelware with a basket pierced with holes that fits down inside are commonly used. You can just float the tomatoes a few at a time into any cauldron of hot water and fish them out with a slotted spoon when the skin starts to peel and crack. Then you need to slip them out of their skins, which is easier if they cool a bit on a platter. They should scoot out of the skin when squeezed into your processing pot, while you are left holding a little bag of skin which your chickens will love (or failing that, the microbes in your compost would love them too.) There are other ways to do this besides standing over a pot of scalding water, and I recommend them. My Grandma used to stick a tomato on a fork and hold it over the burner of the gas stove til the skin split and curled. But for lots of tomatoes, and to add lots of flavor, I really really likegrilling them or using the oven. For salsa and hearty sauces, a barbeque can't be beat, and for milder ones, the oven is great. You can do a big batch and then let them cool in a shallow pan, then slip them out of their skins into the jars and top up with the flavorful juice that collects in the pan--instead of being diluted and lost in a pot of water.
I have been canning for 35 years, and a lot of that was in a cabin with no electricity, so there was no fridge or freezer. I love the convenience of canned food--you can take it anywhere, and when you open it it is ready to eat. All the work is on the front end. So you don't have to thaw it ahead, cook it, refrigerate it, and so on. BUT you need to make good decisions on the front end also, and do the work carefully, or you can hurt people. So, if you are canning tomatoes, you should decide whether you are going to want to pressure-can them or can them by the old hot-water bath method. Both are good, they just have different uses.
A pressure canner is used to attain heat above the boiling point of water. Thus it can kill different kinds of spoilage organisms. The way that you decide which kind of organisms will grow in your product, and thus the kind of canning process to use, is by figuring out how acid your product is. Deadly spoilage organisms like botulism can not grow in an acid ( or super salty) environment. Therefore, acid produce like fruits, and salty/acid things like pickles, can be preserved safely without pressure canning. Water-bath canning can kill the organisms that cause rot and mold, so if there is enough acid present, that's all you need to do. HOWEVER, if your acid product has a bunch of non-acid items like peppers or olives or celery or nuts in it, then you need to pressure can. And if your tomatoes are low-acid types with a very mild, not-tangy flavor, then those need to either be pressure canned or get a little dose of additional acid. You can use citric acid from the store, lemon juice, or vinegar, bearing in mind that vinegar evaporates and needs to be added at the end of cooking. How do you know whether to add acid? You can taste and guess. You can just add it all the time. Or you can go to the garden store and get a pH tester so that you know. Litmus paper will work great. If you are canning tomatoes plain, a basil leaf or a bit of olive oil will not hurt your acid balance. Spices in sauces won't hurt. But chunks of the aforementioned vegetables will cause you to pressure-can. Basically, you can pressure-can anything you want--it's just a matter of looking up the processing time, based on the food involved, the size of jar, and the most spoilage-prone ingredient in the recipe.
To (finally) get to recipes: Once the skin is off, you an use a blender or food processor, or two knives, or a chopping bowl to get them to the texture you want for salsa, sauce, dice, or whole tomatoes. You cook them into the form you want--salsa, sauce or whatever--and put that in jars. This website has some good and trustworthy salsa recipes You will need to pressure-can pasta sauce if it has mushrooms, celery, meat, or similar no-acid chunks. If you stick to canning a nice smooth tomato sauce with just a few herbs well-cooked in the sauce, you can do that in a water bath. Or you just stick the skinned tomatoes directly in jars and process that. My recipe is : Roast the tomatoes in the broiler or grill (I do some of each, and grill all my salsa tomatoes.). While the tomatoes are roasting, infuse some basil leaves in oil over a low flame. Put your tomatoes in the jars with tongs, add a 1/2 c of the liquid that oozed out of them in the oven along with a pinch of salt, 1/2 teaspoon lemon juice and 1/2 teaspoon of the oil. (Add lemon juice as called for in your canning guide, based on acidity of the tomatoes.) You can go online and find all kinds of wonderful recipes, but by and large, if you are going to can, keep it simple at the canning stage and add the fancy stuff later. For one thing, it's hard to predict how much of which recipe you will want. For another, they will taste different after heat-processing and aging in the jar. Spices that taste great in fresh-cooked dishes--like garlic--will get bitter. Chiles will gain heat. Salt balance will change. Sugars will caramelize. I once canned some sweet-sour venison that when opened was almost charred because sugar caramelizes at a lower temp than pressure canners reach. So, complex or untested recipes are better frozen. The next step is the actual canning.
To process: Wash your canning jars well. Set the lids (not rings) in a saucepan and bring them to a boil, then let them sit. If you are super cautious, sterilize your jars in boiling water or a dishwasher. (I don't do this step because the processing time should sterilize clean jars.) Then fill each one with tomatoes from your platter of skinned tomatoes (or your vat of salsa or your pot of sauce.) Fill them within an inch of the top. As you fill each jar, wipe the rim carefully with a paper towel or a clean rag wrung out in hot water. Any little bit of pulp or juice on the top of the rim will prevent a seal. As you wipe each jar, place a lid on top and screw down a ring over the lid. Finger-tight is perfect--neither loose enough to leak nor torqued down super tight. place it in the canner, on a rack or disk of perforated metal (or anything else that will keep it off the bottom and not disintegrate--in a pinch, a disk of plywood with holes drilled for air bubbles to get through.) To figure the times, I really like Rodale's book Preserving Summer's Bounty. They not only discuss acid levels and the effects of altitude on canner times, but things you wouldn't think of like the way that hard water will neutralize some of the acid if you put it in your jars. Or try this website for some dowdy, but solid information.
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