I just recently bought a Presto 6 quart pressure cooker. I have never used one for cooking before, but it sounds like it should be great. I also got it because this small 6 quart will hold 4 pint jars in it, which is good for me when canning small batches. Really, I dont often have large batches.
So I bought the Presto for $49.00 from Amazon, and it looks like a decent unit, though made in China. All Stainless steel, and pretty simple and basic, with a simple fail safe mechanism that keeps you from opening it when under pressure.
Some pictures of it:
But the manual does not reccommend it for canning for some reason. And also, the instruction booklet does not say what pressure the weight is calibrated for. Although the instructions do mention that at 15 lbs pressure, a cooker will reach 250 degrees. But it doesnt say that it refers to this cooker.
So my questions are, does anyone know what pressure these weights are calibrated for?
And, my more ambitious question, are the weighted steam vents fairly interchangable? I have a 22 quart mirro unit from the 70's, and it takes a weighted gauge that you can set for 5, 10 or 15 pounds. All of the pressure cookers I have seen, regardless of size, appear to use the same type of weight, whether they are a 10 quart or 20 quart.
Is is worth it to get a new stem and weight and upgrade my presto cooker to another type of weighted gauge? I realize canning is detail-critical, so I would not do it unless I could be very very certain I am doing the right thing. I also do not mean that I would just use the weight from my mirro canner on the presto unit - I mean unscrewing the stem and replacing it with, for example, a mirro stem and weight.
The top of my Mirro canner:
Any advice is appreciated.
A corner of my small garden is below. The terra cotta planters had my first test of potatoes. They started out really strongly in May and June, but the growth died back significantly during the heat here in the north east in July and August, and when I pulled the plants in early September, I got about 5 small potatoes, totaling no more than 12 ounces. I have to figure out what went wrong.
Thank you for any advice,
What you are proposing is exactly what I did when I bought a National 7A that had a pressure gauge. I had a 6qt mirro that I got at a yardsale, guess they clogged the vent and blew out the pressure relief (slightly warped the bottom but not bad). I took the pressure gauge of my 7A and screwed in the vent tube, perfect fit. I then ordered a new vent tube when I ordered a new pressure relief and a gasket. I now have a 6qt, 12qt, and 16qt canner that all use the same weight (I have 2 weights). The 6qt is GREAT for trial batches! I just trialed black beans and did 4 pints. It worked great, now I'm trying to find black beans in bulk to put into quarts.
I would go ahead and take both vent tubes off and see if they fit. If so, go ahead and order another. They run about $8 or so last I remember. You may be better off finding one at a yard sale if you aren't in a hurry, can probably find one of the 4 or 6 quart cookers for pretty cheap, even if its been blowed out like mine was. Check ebay, there is a guy on there right now selling canner parts and has a vent tube and weight for $10 shipped. Just let him know the vent tube with the pointy end needs to go with the weight, he switches what goes with what in the auction. If you can get him to agree to that then for the price of just the stem you'll get the stem and the weight.
My limited knowledge of the subject comes from a BYU series called living essentials. The expert said that cookers had metal that was pretty thin and not a good heat sink allowing too much temperature and pressure variation in the canning cycle. That could make the canned goods unsafe / not fully processed. She advocated only using a pressure canner. They are apparently different enough.
This may be the show, she did a more generic one on canning as well.
Thanks for the info so far. I may strongly look into what Spudgunr suggests. I am almost positive the stem size of the vent tube is the same, almost a standard, size. The new presto's seem to have only one setting, and it does not show what pressure it it. Below are photos of the presto weighted gauge, showing the top and bottom. Only one hole, and nothing but a part model number.
If this works, I agree, it would be great for small batches. In my small garden, I get moderate amounts of green tomatoes that fall off. The Ball book has a great green tomato salsa recipe, but I can only make a few half pints at a time. The small pressure cooker would work great for this.
The bottom of the gauge that goes onto the vent tube:
Thank you again, great information.
I cant guarantee that the switch will work, from what I had read National later turned in to Mirro, which may explain why they are threaded the same size. But, if they are approximately the same diameter at the base they'll probably swap, I'm sure they use one of the standard taps. Go grab a wrench and in 15 minutes you'll be able to tell us if they swap. If it does work please do let us know as then I could expand my canner collection if I found a cheaper presto, knowing I could swap the parts.
Edit: Just kidding, National turned into Presto, not Mirro. I'd say you have a pretty good shot of them swapping then.
Ok, here's a brief update, until I can spend a little more time on this later in the week. The new Presto stainless cooker has a vent tube that has a nut inside the canner, the thin metal of the lid has about a 1/4" hole in it. No threads in the lid, since it is thin, and the tube tightens against the nut.
The older mirro actually threads into the thicker lid of the aluminum. I can't gauge the thread now, its around 3/8" and finer than 16 tpi.
But overall, I think I can drill out the new presto, and add the older stem of the mirro. Instead of tapping the thin metal, I can easily fit a thin nut inside, if I can find one in brass or stainless. If it leaks a little steam, I think I can cut a thin gasket out of one of those silicon baking forms. They take high heat, and are food safe.
I will follow up with photos later, and any other insights are still welcome. I'll post how it turns out.
ETA: I see Dragracer Rob points out that the thin metal of a pressure cooker versus a true canner may allow too much fluctuation in temperature, and produce a bad product. This merits some looking into as well, although if the pot maintains an even pressure, I would think the temperature should remain within the range as well. Interestingly, it seems most canners are, in fact, thicker aluminum, rather than thin stainless.
I got about 3/8 and about 30 TPI. I cant find my thread gauges though so its probably 32 TPI (which would be 3/8 extra fine thread). Also, it may vary a bit, but if you keep draft off it and keep the weight moving how much variation can there be? I can see how it'd be an issue on dial gauge canners, but with the weight doing the regulating, so long as the weight is moving you have the right temperature.
Edit: And on the up side, you already know all they did was drill a hole. You can do the same thing if you cant use their nut. The top is the best spot since they probably flattened it a bit to make a better seal.