Yes, you can can just applesauce with nothing in it, but it will brown and lose some flavor. Sugar or acid helps it keep that golden color and crisp taste.
Too much fat creates a barrier that ruins your seal, so that can be bad, but even fairly fatty foods can be pressure canned it you are not getting a solid layer of fat on the top. It is harder to get meat products totally safe, so I don't bother often. It is much easier to freeze them.
I pressure can all my tomatos so that they are sweet (no acid added). I also can my pasta sauce, BBQ sauce, ketchup, beans and veggies that are not pickled. Yes, you do end up with soft, canned veggies, but that is alright for somethings. Soups can well too, of they are dairy free and low fat. I hot bath can my pickles, fruits, jams, fruit sauces, and relishes. I never boil anything for 10 minutes after opening. Any microbe that can survive a pressure canning session will suvive a 10 minute boil. I'm a microbiologist by training, and that is just silly. It comes from old glass canning jars where it is very hard to tell if a seal is broken. That being said, home canned goods can go bad. So never eat anything that emits a vapor or gas on opening, or that has developed fizz or bubbles that rise and pop after opening. Never eat something that wasn't sealed when you went to open it, or didn't "pop" when opened. Eat home canned foods within a year. Don't eat anything that has a noticeable change in color, texture or smell. Properly canned and stored food will look the same from the time it fully cools out of the canner until the time you eat it. The only exception is if you can in plain water, then fruits and veggies near the surface will brown, and all will soften slightly. Canned goods should be stored with rings removed in a cool, dark location.
My favorite reference is the
food lover's guide to canning. It is out of print, but you can find used copies. I also love the
joy of pickling
, because I love pickles!
ETA: purees have to be watery to can well. All home canning is water based (water packed) and really thick purres have too many air pockets. It is better to can the veggies in chunks, and puree once open. Apple butter is about the thickest consistency you can can safely. Following recipes is very important in hot water canning, as they must meet levels of acidity and/or salt or sugar laves to be safe. You can fudge and fiddle a bit with pressure canning, as long as you follow some rules. Meat and dairy require high pressures and very long processing times. Most home canners avoid adding those for that reason. Fats and oils can ruin your seals, so require extra caution and care. That said, I'm looking forward to canning my own
fish in oil this season, so it can be done! Salt and sugar help maintain taste and texture, so cut them out with caution. There is a reason canned goods in the store are low sodium, not no sodium. Things canned without sugar or salt end up tasting a bit bland and get very soft and squishy. It won't kill you, but your family might wonder why you are feeding them this glop.
Edited by lunarlady - 1/3/11 at 5:26pm