Many years ago in my blacksmithing obsessed days I was often found cruising metal scrap yards for treasures and steel stock. Every time I’ve moved, my accumulated scrap pile has come with me. One day I spotted a large stainless pool filter, complete with lid, at my favorite scrap yard. I knew right away that I wanted if for boiling large batches of oak bark for tanning hides. I figured it could be useful for other stuff too, so I bought it for a mere 20.00.
It took me many years and quite a few moves with the scrap metal pile in tow to finally get my bark boiler running. I put a scrounged copper pipe and a gate valve on the bottom outlet and fired it up to boil some bark. My suspicions that it was awesome were definitely confirmed. An open fire can be used directly under it which saves a lot of propane, and when cooking is completed, the liquor can be drained off from the bottom. Using the bark boiler is a huge improvement on boiling batch after batch of shredded bark on the stove top.
I had the boiler running for a year or so before it ever occurred to me that I could use it for canning food. I needed to pasteurize some fermented grape juice in the bottles and they wouldn’t fit into a canning kettle. So, I busted out the bark boiler. Amazingly, 19 champagne bottles can fit in the bottom layer, with room for another layer above that! The experiment went well, so the bark boiler donned its second hat, that of Mega Canner.
Tomato canning can be a big production around here. We shoot for about 100 pints a year and they come off the plants in large batches. Half the day in the kitchen blanching, peeling and packing into jars and then all those suckers still have to be water-bathed. Try this scenario on for size (I’m sure a lot of you have) Fit as many jars as you can in the kettle, boil the kettle for 45 minutes or more, turn off, allow to cool somewhat, remove jars, allow the water to cool a bit, add new jars, bring back to a boil, and repeat it all over and over again while dragging your timer around the property trying to get other stuff done. It’s often hot and the kitchen gets steamed out. The Mega Canner can fit hours and hours worth of water-bath canning into one firing that doesn’t take much longer than canning one kettle of jars on the stove top. The Mega Canner has room for a helluvalotta jars holmes! If it can fit 38 champagne bottles, imagine how many quarts or pints it can hold. I don't know. I've never come close to filling it up and I'm too lazy to bust out cases of jars to find out.
The Mega Canner/Bark Boiler could also be used for distillation with some very slight modification and to boil all manner of large batches of stuff. It started its life as a pool filter. Stainless pool filters are fairly common, but most are pretty small in size. This is the largest one I’ve ever seen, though it seems likely that they are made even larger. The walls are very thick, much thicker than a pot or a barrel. It has a perforated grate on the bottom which is mighty handy for both bark boiling and canning. It does still smell of chlorine a little. Steel is minutely porous and chlorine has probably bonded with the surface of the metal. I may at some point sand off a thin layer of metal from the inside to get rid of that. for now though, no food contacts the water or metal. There are various grades of stainless steel, and the metal composition of this one is unknown, so it may not even be food grade. Finally, the drain pipe and plumbing on the bottom are bronze and copper which are not food safe either. There are two drains on the bottom. One drain is plumbed already and the other has a bronze cap.
To use with a fire, I set the legs on 3 bricks or rocks to raise it a little. This system could use some improvement for efficiencies’ sake. A rocket stove furnace which it could be set over would be pretty ideal. A rocket stove would be cleaner (complete combustion), faster, and would use much less wood. That project however will have to wait for a permanent outdoor kitchen to be built. When its dry out and high fire season, which is almost half the year, a propane burner from an old smoker substitutes for the fire. The burner is super high output, so you can really crank it up for fast heating. A piece of aluminum flashing is used as a windscreen with the propane burner, which really helps keep the heat under the pot.
I have seen quite a few other pool filters at scrap yards and such since then. Most are pretty small, but some are large enough to be useful as canners. Craigslist has a lot of them, but most of them are not very useful shapes. A lot of them have lids that are as tall as the bottoms, which is fairly useless for canning. Some look as though they are made from other materials, and even the stainless ones are often painted, but persistence in hunting pays off and there must be more similar to mine out there.
I think a better option for a lot of people might be a full sized stainless steel beer keg. The larger size known as a half barrel is 16 x 23 inches, though it has less actual inside working room than that due to the standing rims on the top and bottom. Cut the top off, have some handles welded on, and you’ve got a good sized food grade stainless cooker that you can also use for scalding turkeys and chickens for plucking, and for who knows what else. I would add a heavy stainless or aluminum screen or perforated plate for canning as the jars must always stay off of the bottom of the canner. Stainless drums are fairly common too. They come in sizes from 15 gallons and up, A 30 gallon drum with copper/bronze plumbing for a bottom drain and a lid ought to make a fine large boiler that would fit almost any amount of stuff a body desired to boil at one time. Of course stainless isn't essential if you aren't cooking food or tanbark directly in it, so there must be other items out there of aluminum or steel that could suffice. The bottom drain is also not essential, just convenient... unless you want to put it on a stove top, then it's actually inconvenient.
not every one cans large amounts of jars at once since that requires large amounts of food to be canned, and I only do so a couple times a year. But, if you are into homesteading, or are serious about subsistence activities, you probably will sooner or later. I’ve often had two stove top canning kettles running at one time, and that helps with the time and hassle when processing a lot of jars, but Mega Canner still kicks major butt on that scenario if there are a lot of jars to boil, such as when processing a bumper tomato crop or canning juice. If anyone wants to take my bark boiling mega canner away, they’ll have to pry it from my cold dead fingers. If you do a lot of canning, or plan to in the future, put large metal containers on your radar! That is probably my best canning tip besides don't can stuff you don't eat.