You have to know the rules before you know which ones to break.
My name is Crazy Jar Lady and I am a rebel canner.....
With that being said; there are some rules established by the USDA that I will not break. One of them being most low-acid foods going into the pressure canner. There are some folks that waterbath everything as that is all that used to be available. One of these days we will have a science lesson and go over the big B (botulism) and how attempting to destroy it affects our food.
Basic rules: water bath canning (top temp 212 degrees) is for high acid foods, specifically 4.6 pH or below, like tomatoes and their various products, fruits, jams, etc. Pressure canning (top temp 240 degrees) is for low-acid foods, such as meats, soups, vegetables, etc. USDA has established processing times for common items and you can find that information in several core books. The safest thing to do is to educate yourself. I will also make a post about canning books and ones that I prefer.
Now.... The USDA hasn't had the time or the funding to test every little thing. Common sense has to come into play. Processing times are based upon the temperature of the product rising inside the jar, while inside the canner, to the necessary level to kill off the bad germs. So a thicker product equals a longer processing time. Example: grape juice (thin like water) is 20 min and salsa (chunky and thick) is 40 min, both water bath.
You're also going to find lots of conflicting information. Somebody says one thing is ok. Another person does it another way. Their grandma did it that way and their mom-in-law taught them something else..... Go back to the book. Keep that book handy. Say you get a deal on a pile of pears and you just want to can slices in a light syrup. Having a basic canning book on hand is going to give you that information quickly without having to get online or call grandma and wake her up.
I am in no way telling you to do as I do! I am only telling you what I did and how I did it. I am NOT telling you to do it!
My Ball Blue Book is from 1960. Here's where my rebel comes in, mostly in pressure canning. I have successfully canned sausage gravy, milk, pumpkin puree, bacon.... all items highly contested by the "pearl clutchers" and not tested by the USDA. I use times listed in the 1960 book for basic items because alot of the newer recommendations are so out there. Have they lost their damned minds?! Pressure canning tomatoes?! Come on..... Some people are just flat out pressure canning everything; talk about losing flavor and vitamins that you don't need to! You don't need to heat your pineapple to 240 degrees Margaret.....
I get a little worked up about this.
Very often, you come across great deals on gallon cans of various products and that is just too much for your household at once. It's simple to portion it out and re-can the item so it's shelf stable. This also tends to be frowned upon.
Let me drop one more bomb: some low-acid items do not survive the pressure canning process very well. Sweet corn, especially the super-sweet varieties tend to scorch. Meats in sweet or heavily flavored sauces also tend to burn; sloppy joes, taco meat, bbq pork, etc. If you KNOW the item you're canning is going to be heated to boiling 10 minutes prior to eating it, waterbathing these low acid foods is a viable option. (Again, some folks still just waterbath everything.)
What is a "pearl clutcher"? Picture a sweet southern lady being offended, the sharp intake of breath at whatever expletive that was uttered, the hand to the chest, grabbing the ubiquitous string of pearls around her neck..... When rebel canners talk about all the different things they can; panties get bunched. We are going to poison our families.... blah blah blah
You're not going to poison anyone if you use common sense, know the rules and the reasons; and know which rules can be safely broken.