You definitely need something between the layers to distribute the weight evenly.

I used to stack the old jar cases and it worked ok- no seal failures that I remember. But now that they aren't full boxes, they really don't work.

You've got a couple choices if you don't want to lose more of your lovely home canned food than is necessary:

One is to buy boxes that fit:

http://www.uline.com/Product/Detail/...rrugated-Boxes

And these fit quarts: http://www.uline.com/Product/Detail/...rrugated-Boxes

You can also get much heavier weight boxes- 275# test weight- for just about twice as much money. However, if you are planning on using them for storage and stacking them, it probably is worth it.

I no longer stack cases of full jars, because we designed and built a whole bunch of these:



I have 8 of them (6 sized for cases of pints- they hold 11 cases, and 2 for quarts- they hold 9. We tied them together into two groups of 4 each... one is against a wall, one is free standing. The free standing one actually works slightly better, because you can push the cases through from the back a bit to get ahold of them better. I've been thinking of making some rope handles for the boxes on the shelves against the wall, as it's a PITA to try to use my fingernails to get ahold of the edges of the box to pull them out.

But then, I was trying to maximize space, so designed the shelf units to JUST barely fit the boxes. If you made them an inch or so wider, they'd be easier to work with, I suppose.

(oh, and these boxes are just large enough that you can fit the "case" the jars come in inside them- it reinforces them a bit, and also holds the jars more solidly than the box alone)

The other choice is to buy some press board or thinnish plywood (1/4" should be strong enough) and cut it into pieces the same size as your canning jar cases. Put one piece between EACH level of jars... and I wouldn't stack them more than 3-4 high, because you still have weight directly on the jar seals.

While leaving the rings on MAY help preserve seals a bit if you do have to stack them, it also risks rusting the rings (so they won't work well when canning more) and a ring can "mask" the fact that a jar isn't well sealed.

Summerthyme