I've copy/pasted a post I wrote on July 22, 2010, here b/c the entire thread contains several misleading posts. I wrote near the end of the discussion, kind of a rebuttal to some possibly harmful statements by others:
>>Often, heirloom varieties are more acidic than modern hybrids, although to what extent I can't say and refuse to rely on. Regardless of the varieties I've canned or made products (e.g., spaghetti sauce) from for canning, I have always added lemon juice or citric acid powder to the tomatoes / sauce before canning them. We want acidity in hot-water canned products. This is what provides the safety margin for non-pressurized canning: acidity. Low pH.
On the subject of canning (and this is mostly for those new to the practice or wanting to try it out):
I learned from books. This means that you can learn from the web and from books, too. No one I knew canned or even knew anyone else who did when I was faced with a friend's tree absolutely laden with cherry-sized plums way back when.
Rule #1 of Canning:
There is no such thing as "too safe" when home-canning foods.
Do not improvise your own cooking times or preparation methods. Do not take chances with the safety of your family or friends. If you can afford to purchase only one canner *and* can afford a pressure canner, do so. Both kinds of canning (hot-water bath and pressure canning) can be performed in a pressure canner; the reverse is not true. I got along with a hot-water canner (also referred to as a "baine Marie") for several years before I felt comfortable enough to look for a pressure canner, but the web wasn't around then, and printed info on pressure canning wasn't all that encouraging.
Now it's different; there is a TON of information, but not all of it is reliable. Unfortunately. Know your sources. The Ball Blue Book is excellent; the USDA extension nearest your home is also excellent.
I can tell you that I have experience, but I will also tell you that I am *not* experienced in canning at elevation or in canning meats. I have also not done much canning of quarts; most of what I've canned has been jelly-sized jars, 12-oz. jars, pints, and 1.5-pint jars. Each of these has a *different processing time* which is dependent on its size and on your elevation. Find out what that processing time is from a reliable source: again, the Ball Blue Book or the USDA.
Rule #2 of Canning:
There is no such thing as "too clean" when home-canning foods.
Even after years of experience, I still demand almost hospital-like sterility from my jars, flat lids, and screw-on bands. I want my food hot hot hot when it goes into the jars, my water boiling, and my jars / flat lids sterile (or as sterile as I can get them). My own hands are clean clean clean. I do not touch my hair or my face while working with the jars. If I do, I wash my hands again before touching a jar.
If you have a dishwasher, you're golden: put the jars and the screw-on bands on a good, hot cycle as you're getting the food ready for canning. Turn the dishwasher on. The jars and screw-on bands will wait for you. Hand-wash, in soapy hot water, the flat lids. Yes, even if they *just* came brand-new out of the box. Rinse them well. Have a bowl or small pot into which you can lay them without them sticking to one another. I turn them alternately right-side-up and upside-down. Then pour boiling water over them. They will also wait for you.
Now your equipment is good and clean.
Prepare/cook the food, fill the jars per your recipe (head space varies, depending on what you're canning), and make very sure there are no particles of food on the rim of the jar. Place the flat lid on the rim of the jar and a screw-on band over the lid. When you have a rack of jars filled (usually 7 jars) *and* the water is boiling, place the jars into the water. There should be enough water to cover the jars by 1 inch when the water is boiling.
Rule #3 of Canning:
Follow established procedures, and you will get it right the first time.
After the prescribed processing time has elapsed, use the "jar-lifter" and place each jar carefully onto a folded towel which has been set in place out of drafts. This is where the jars will cool, probably overnight. My best counter for this cooling is next to the stove but also next to the window, so I close the window *sigh* when the processing time is almost up. After all my work, I do not want a jar to crack....
There's a nice "ping" sound when the lids invert. Count these pings; you'll know whether all the jars sealed or not. If any did not seal, those go into the refrigerator for eating in the near future; do not put them in long-term room-temp. storage.
And feel good about yourself!
Sunset Zone 17, USDA Zone 9