If you were lucky, and got a bountiful tomato crop this year, you will want to preserve your harvest.
Canning is a food process that was invented during the Napoleonic Wars, and mushroomed in popularity afterwards. Tomatoes are probably the most commonly home canned food. It is really nice, when it is pouring freezing rain outside, to reach into the pantry for a bag of pasta and the tomato sauce you canned the previous summer. You smell the tomato sauce and for a moment it is August again.
*CAUTION**
From a public safety point of view, foods with low acidity (a pH more than 4.6) need sterilization under high temperature (116-130 °C). To achieve temperatures above the boiling point requires the use of a pressure canner. Foods that must be pressure canned include most vegetables, meat, seafood, poultry, and dairy products. The only foods that may be safely canned in an ordinary boiling water bath are highly acidic ones with a pH below 4.6, such as fruits, pickled vegetables, or other foods to which acidic additives have been added.
[thanks to Wikipedia]
Tomatoes are just a bit under the safety mark of 4.6 ph, and if you want to produce a product that is safe to eat, you have to follow best practices of cleanliness and sterilization.
You will need:
A pressure canner if you plan to put up anything besides fruit and plain tomato chunks
or puree.
A very large pot with a lid and a rack on the bottom (canner) if you are only canning
plain tomatoes
Canning jars. Don’t use just any old jars you have lying around. They (literally) won't
take the heat. Real canning jars are inexpensive and widely available
If you use normal canning jars, you also need lids and rings.
Jar lifter tongs and a wide mouth funnel.
A timer
You will also need:
A canning book, which gives exact directions and times for canning. My canning Bible
is Putting Food By -- http://www.goodreads.com/...
Other good references are the Ball Blue Book, available at www.lehmans.com. Lehmans, by the way, is a well known mail order house that sells supplies to the Amish and others interested in off-the-grid living, and has lots of canning stuff.
A third book I can recommend is Preserving Summer's Bounty:
http://www.amazon.com/...
The first step in canning is to make sure you have reduced the bacterial load as much as possible. Scrub your kitchen and make sure all of your utensils are clean. Wash your tomatoes in hot water. If you have a dishwasher, wash your jars in it. If you don't scrub the jars, fill them with hot water and put them in a big pot with 3-4 inches of hot water in it. I like to boil my jars for ten minutes, whether or not they are going into the pressure canner.
If you are dealing with two quarts of tomatoes, have lots of time, or have many willing and helpful hands aiding you, you can then peel the tomatoes. If you don’t, try this:
(1) Cut the tomatoes in big chunks and dump a couple of cups at a time in a blender. Blend until liquid.
(2) Dump the liquidized tomatoes into a food mill (also known as a mouli) The medium screen will strain out the seeds and leftover bits of skin. COOKS ILLUSTRATED [www.cooksillustrated.com] suggests that blended tomato skin adds flavor.
You now have raw tomato puree that you can (a) cook down to a sauce consistency and can (possibly adding a little salt, citric acid or lemon juice) or (b) carefully cook down to a paste consistency and can - watching that it doesn’t scorch or (c) cook down to a sauce consistency and add your choice of other vegetables, herbs and spices for pasta sauce. If you choose (c) you are going to have to pressure can your jars, because things like onions, garlic, celery and carrots have a higher ph, and your sauce will have a too high ph to safely can in a boiling water bath. I would avoid adding meat to the sauce. Meat is very high ph and has a normal high bacterial load. If you like sauce Bolognaise, add the meat when you cook your meal.
Following the directions in your book, fill and cap your jars. Make sure the jar rims are wiped clean with a paper towel dipped in hot water, or they won't seal. The larger jars you use, the more of a chance you have that the jar will not properly heat through, so I like to can in wide mouth pint jars, which are just the right size for pasta-for-two. I have a big, American made pressure canner heating on the stove while I am assembling the sauce jars. The jars go in the canner -- use your jar lifter tongs and potholder gloves, boiling water can scald you-- the lid goes on the canner after I make sure that the jars are evenly spaced and only the lids are touching-- and I tighten up the hold downs
The canner has to exhaust for ten minutes - with a good steady geyser of steam out of the vent -- before you close the vent, bring the pressure up to ten pounds and set your timer.
When the timer rings, let the pressure go to zero and take your jars out. If you did it all right, the jar lids will suck down with a loud pop after they cool for a few minutes.
It's a lot of work. You can now congratulate yourself on following a hundred and fifty year old tradition and giving your sun ripe tomatoes a little bit of longevity.