I make kimchi in mason jars. (two gallons last weekend) I use half gallon jars, and leave about two inches on the top. Then I put a ziplock bag in the mouth, and just flip the zipper over the edge of the jar. Then I push the bag down onto the kimchi to pack, (careful not to tear it) and then fill the bag with water. The lid goes on next, then the threaded ring. It will thread right over the thin layer of plastic. (again, careful not to tear) The water holds the kimchi down, and the plastic layer in the threads lets just enough air out. The water will also come out as the product expands, so I put a tray under my jars for that. I refer to it as a home made air lock.

I have never had problems making sauerkraut in mason jars. The online hucksters trying to sell expensive air-lock pickling jars insist that mason jar lids are not airtight unless heated during canning, but that has not been my experience. I use the burp method, in which the lid is kept tightly sealed, slightly loosening the lid once or twice a day to release the gas pressure. If the lids were truly not airtight, they wouldn't hold the pressure. That said, wire bale canning jars, like the Fido jars from Italy, are sooooooooo much nicer to use than ordinary mason jars. Burping the jars is much easier, and they'll actually burp themselves long before the pressure can build up enough to explode the jar.

Yes, you can use mason jars. I make kimchi in them all the time. Just make sure they are sterile (pour in some boiling water and dump it out) and make sure the shredded cabbage is not exposed to air (fill with brine up to the very top). Also, don't screw the lids on super tightly. If you make a truly airtight seal, the gases will not be able to escape and if enough pressure builds up, it could crack the glass. Highly unlikely, but possible. I'm not sure what you mean about placing the head of cabbage on top. I would just top off the jars with brine. Here's some more good info on kraut:

http://www.wedlinydomowe.com/food-preserving/sauerkraut/fermentation-sauerkraut

I am doing my fermenting in fido jars, based on the results from Sourkraut Survivor http://www.nourishingtreasures.com/index.php/2012/07/03/sauerkraut-survivor-final-report/

Specifically, the fido will create a seal that will allow gas pressure to leave (so the jar doesn't explode), while still not letting additional oxygen into the jar. Mason jars will occasionally need to be "burped," but will also allow air back into the jar while this is happening, which will change how the lactofermentation proceeds.

Currently I have some kimchi and my water kefir fermenting in Fido jars. Might make some Cortado :)

But, unless you have serious gut issues and/or specifically need the probiotics, I wouldnt let a lack of jars prevent you from fermenting. If you don't see mold, the mason jar will be fine for starting out.

I tried to do it in canning jars, mine just rotted, but then again i did not use any technique other than throwing the cabbage in jard with some brine to see what happens

I've done it in Mason jars, but I've had more success with Pickl-it jars - and I don't end up scraping off a bunch of the top. I make enough fermented stuff to justify buying a few of those jars. There are also lots of instructions online for how to install a regular cheap airlock into a Mason jar, with properly sized gaskets and all.

It's a tricky question as too much pressure can break the jar but the pressure is from the yeast. The yeast is fed by the sugar or fruit that is in the kimchi or sauerkraut ( same thing, different spices ) and they consume the oxygen and produce the CO2. CO2 is heavier than O2 so even in a leaky jar, it dispels any oxygen from entering the jar, solving the mold problem and killing off all the aerobic microbes including the yeast. With sealed or partially sealed jars, the added pressure helps the fluids penetrate the vegetables. The salt only needs to be on the vegetables temporarily for about half an hour before the vegetables are packed in the jar and can be brushed or rinsed off, the salt reduces most of the bacteria except Lacto Baccillus which hopefully will outnumber the other bacteria quickly. Lacto Bacillus produces lactic acid which increases the acidity and the sourness of the liquid, killing off the other bacteria and the yeast and this is what preserves the vegetables, the active Lacto Bacillus bacteria. A mason canning jar is actually designed to vent out but not vent back in, that's how the cans seal themselves in a canner, the heat increases the pressure inside the jar, venting gases out and then when it cools, air can't get back in. So long as the jar rings are only finger tight, it shouldn't explode when making sauerkraut or kimchi. The Lightning or French jars with the hinged glass lids with gaskets and a clasp are more of a seal and will hold more pressure which is why they are no longer advised for canning, but they too should vent before exploding. However if you are uncertain if the lightning jar you have is strong enough for the pressure, you can use an elastic band on the clasp or a weight on the lid.

Using the end of the cabbage to hold down the rest of the veggies is a good idea, usually a stone or a dipping dish is used. However that end of the cabbage will be exposed to the air and subject to mold and other microbes so you will want to salt it heavily ( have the salt crystals standing on it ), some people just have a layer of heavily salted leaves on top.

The Hartz and Pickl-it jars are interesting and may be appropriate for pickles and sauerkraut but I think the added pressure and carbonation adds a nice touch to the kimchi so I wouldn't have any problems with using smaller mason canning jars sized for one head of cabbage each. Just make sure they are canning jars with the two piece lids as they are stronger and designed to vent out but not in.

I use mason jars either with a regular lid I vent twice daily or a homemade airlock device (airlock and rubber stopper from the home rea shop for about $4--they drilled a hole in the jar lid for me).

Recently I got glass weights on eBay to weigh the veggies down.

As others have posted, the fermentation process causes the release of a considerable amount of gas. I make sauerkraut in a wide mouth ceramic vessel and simply cover the vessel with clingy plastic wrap. I then secure the wrap with a rubber band. This way gas can escape yet it prevents insects from getting in.

Once the fermentation is done you can seal the container.

_Lazza

PS - I will be starting a batch of sauerkraut tomorrow. Sauerkraut is great stuff. I hope those who haven't made their own give it a try. It's very easy (, ... do a Google to learn more).