When canning, headspace can become a hot topic. Let's discuss....
Every canning book and instructor will tell you to leave so much headspace in the jar. This means that the jar is only filled to a certain level inside in order to allow the product to expand during processing. Heat makes things grow. Headspace isn't really a determining factor of the shelf life of your product. It really is a functional issue. Now Margaret; before that vein in your forehead bursts... just look away.
The whole point of canning is to heat the product to a temperature sufficient to kill probable germies AND create a vacuum inside the jar. The vacuum seal keeps any new germies from entering the now sterile environment inside the jar. While the product is heating; the air present inside the jar is also coming out through the tiny gap between the lid and the rim of the jar. Very often, the air is pushed out along with some of the product which is known as siphoning. This is where headspace comes into play.
Most recipes generically state to leave one inch of headspace. Let me tell you, that is not the case. As you go through the process of canning and polish your skills, you learn what is correct for your operation and what is not. You will notice on alot of my recipes it will state to leave one and a half inch headspace. That's because I have learned to leave the extra room to stop the product from following the air out of the jar during processing. I do not enjoy opening up a canner to find everything covered in whatever I'm canning. It's a waste and a mess.
Chili is definitely a 1.5 inch headspace item. Apple pie filling, I'm inclined to almost leave 2 inches because it GROWS inside the jar during waterbathing. Applesauce sometimes does this to me as well, I don't like to cook things and then cook them again during processing. Jam/jelly is a quarter inch just because it doesn't move around much and the processing is so short.
Raw packing meat chunks is a different deal. Doesn't matter what kind of meat, if it is raw and you're stuffing it into jars, it will shrink. So you can start with an inch of headspace and by the time the processing is finished, you're looking at 2 to 3 inches of empty jar. When canning this type of product, I place the seasonings in the bottom of the jars first. Then I cram the raw meat into the jars fairly tight. Tight enough I couldn't get a spoon down in there easily, but not so tight it's a rock. I fill them almost up to the rim. After processing, I end up with a nice inch to 1.5 inch headspace and my jars don't look like they are half empty.
Cooked Meat Mix tends to shrink inside the jar during processing as well. Even when I've overcooked it before processing, it shrinks. I fill CMM jars a little above the 1 inch headspace when packing them. They turn out looking pretty nice when I add that little bit more product.
IF you happen to process something and it siphons badly. OR you didn't pack the raw meat in tight enough. IT"S OKAY! As long as there is a good seal on the jar, you're just fine. (Breathe, Margaret. They aren't gonna die from too much headspace. I knew you didn't scroll on by.) I place my jars on the shelves in order of smaller headspace to the back and larger headspace to the front. I like to use the larger headspace item first. Honestly, I don't think it truly matters. I've had Exploding Weinies on the shelf for a couple years now and they are still just fine from the day I canned them; there's all kinds of room inside those jars. Please don't go through the waste and aggravation of recanning something because it isn't pretty. I promise it will eat just as good as the jars you did with the second batch that didn't siphon.
What have you processed that ended up making a huge flipping mess?