Foods of the World Forum Homepage
Forum Home Forum Home > Other Food-Related Topics > Canning, Freezing, Dehydrating and Other Food Preservation
  New Posts New Posts RSS Feed - Pressure---The Next Step
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

This site is completely supported by donations; there are no corporate sponsors. We would be honoured if you would consider a small donation, to be used exclusively for forum expenses.

Thank you, from the Foods of the World Forums!

Pressure---The Next Step

 Post Reply Post Reply
HistoricFoodie View Drop Down
Master Chef
Master Chef

Joined: 21 February 2012
Location: Kentucky
Status: Offline
Points: 4155
Post Options Post Options   Thanks (0) Thanks(0)   Quote HistoricFoodie Quote  Post ReplyReply Direct Link To This Post Topic: Pressure---The Next Step
    Posted: 09 December 2015 at 14:20
Part One

When most of us start canning (or “jarring” as our British members say), we do so by processing foods in a boiling water bath. This makes sense, as it’s inexpensive to get started, easy to do, and safe.

Safe, that is, so long as you follow the basic rules. Acidic foods, sugar preserves, and fermented products can be put by using the boiling water process because their spoilage mechanisms are destroyed, or their growth seriously impeded, by temperatures of 212F.

When it comes to low-acid foods---which includes all animal proteins and most vegetables---boiling water baths don’t cut it. Many of the spoilage mechanisms, which include anaerobic bacteria, such as those causing botulism, happily survive and flourish at 212. To destroy them, or significantly retard their growth, requires sustained temperatures of 240F or higher. The only way to achieve those temps at home is with a pressure canner.

Many home canners shun pressure processing, for various reasons. They believe, erroneously, that the canners, themselves, are unsafe. That they are expensive (which is not true in the long term). That they are difficult to use (also not true). And other reasons.

That’s fine. There is a myriad of foodstuffs that can be safely preserved using a boiling water bath. But if you’re thinking of taking the next step, the following primer might be of some help.

I never intended writing a primer on pressure canning. But Ron and I, over the past month or so, have exchanged several long emails exploring the concept. And I figured it would be a good time to share that info while it was fresh in my mind.

As is usual with these primers, I’m hoping other members will jump in, sharing their knowledge and experiences, posing questions, and so forth. Working together like that, we’ll see who shaved the barber.

For starters, let’s take a look at how a pressure canner works.

Jars of food are places in a large volume of super-heated steam, which raises the temperature of the contents to 240F. Without pressure there is no way to achieve that in the home kitchen.

Old timers believed they could safely can low acid foods by extending the time the jars stood in boiling water. Some instructions talk about two and three hours. But the simple physical fact is, no matter how long the jars sit in boiling water, their contents can never exceed 212F.

It’s important to understand, too, that pressure canners and pressure cookers are not the same animal. While you can cook in a pressure canner (it would take a large volume of food to make this practical, however), it is not recommended that you can in a cooker. The reason for this is simple. The time/pressure figures given in any canning recipe include the heat-up and cool-down time, as well as the actual processing time. Because of their larger volumes, canners take longer to do both.

In theory, small batches---two to four pints---can be processed in a cooker, by adjusting the total times. But no food preservation organization I know of has established comparabilities. All the data is based on using a pressure canner.

So, let’s look at canners.

A pressure canner consists of a large, straight-walled pot, with an hermetically sealing lid. Inside the lid there is a rubber or polymer gasket. The lid will have several holes, all of which are essential for operation and/or safety.

One of the holes contains a rubber or polymer plug. This is the primary safety valve. Should the internal pressure reach unsafe levels, that plug will pop, and release the pressurized steam. I know of no case where a unit was being used properly that one of those plugs let go. I’m sure, however, that if you turned up the heat and walked away you’d return to find the area above and around the canner soaking wet. Wait too long, and the pot, itself, will scorch and burn once the water has totally vented.

As we will see, you need to continually monitor the operation of the canner. So walking away is not only unsafe, it’s impractical as well.

Another of these holes has a metal plunger (which, itself, is gasketed). That’s the pressure lock. When the pressure starts to build, it pushes the plunger upwards, and prevents venting of the steam (and, thus, allows the pressure to build to the point you want it).

If your canner uses a gauge to measure pressure, it will be attached through another hole in the lid. Most often this will be in the center.

Finally, there is a hole with a nipple attached. This is the vent hole. If your unit uses a jiggler, it will be fitted over that nipple at the appropriate time. If you only have a gauge, a special knob will fit on the nipple, to block the escape of steam.

Some models use both a gauge and jiggler, by the way. In theory they act as checks on each other.

All four holes, and their gizmos, should be visible in the lid. This can’t be stressed enough. My first pressure canner, a Mirro model, for some reason had the pressure lock built-in to the handle. If it malfunctions, as mine did, it is impossible to access it for repairs. As a result, that unit has served as a fairly expensive water bath processor almost from the time I bought it. So avoid the mistake I made.

Some manufacturers recommend that the gasket be lightly oiled before use. I’ve never bothered, and haven’t suffered any because of it. My current unit is about 15 years old, gets used every year, and I have yet to replace the gasket.

One thing about pressure canners is that they use considerable less water than do boiling water baths. On the larger ones (22/23 quarts), only three quarts of water are used. Reason for this is you want to fill the volume of the pot with steam, rather than have the jars covered with water. It’s the steam that does the work.

As an aside, this is why many home canners are confused by the USDA’s antipathy to steam canners. All independent tests reveal that they work exactly the same as a boiling water bath, surrounding the jars with steam at 212F, but with considerably less water. One of the reasons is that USDA continues to use “unsafe” and “untested” as synonyms. But I digress.

Also keep in mind that you want as much steam in the kettle as possible. Which means venting the unit. This merely means that once steam starts escaping from the vent in a steady stream, you let it go a full ten minutes before capping it with the jiggler or knob. Doing that removes as much air as possible. Failure to do that can lead to invalid pressure readings.

Next time we’ll explore how to choose a pressure canner.
But we hae meat and we can eat
And sae the Lord be thanket
Back to Top
gonefishin View Drop Down
Master Chef
Master Chef

Joined: 20 September 2012
Status: Offline
Points: 1778
Post Options Post Options   Thanks (0) Thanks(0)   Quote gonefishin Quote  Post ReplyReply Direct Link To This Post Posted: 09 December 2015 at 15:09
    Nice write up Brook, thanks!

   meatsandsausages website has a nice group of articles written on canning and different aspects of canning...among other things of interest.

   I initially overlooked a lot of the website the first few times I visited.  It took me a while to notice that you have to visit each of the titles above in the heading of the page , within each heading they usually have a selectable link and drop down menu with different areas for each heading.

   Look forward to the next segment!

Enjoy The Food!
Back to Top
HistoricFoodie View Drop Down
Master Chef
Master Chef

Joined: 21 February 2012
Location: Kentucky
Status: Offline
Points: 4155
Post Options Post Options   Thanks (0) Thanks(0)   Quote HistoricFoodie Quote  Post ReplyReply Direct Link To This Post Posted: 11 December 2015 at 13:20

There are several factors involved when choosing the right pressure canner for you. Here are a few of the more important things to consider:

Cost. Initially, pressure canners seem like a major investment. You can buy a complete boiling water canning kit---including the kettle, all tools, and even a book---for less than 30 bucks if you shop around. Pressure canners, without all those accessories, can range from about $80 to $150.

A big bite, to be sure. But keep in mind that a pressure canner, if you take care of it, is a lifetime investment. Amortizing the initial cost, over time, compared to the possible savings in food cost and quality, makes the initial price tag all but irrelevant.

Size. There are numerous makes and models available. But they boil down to two standard sizes; 16 quarts and 22/23 quarts. I shouldn’t have to say this, but experience teaches that there is some confusion. Those volume figures refer to the total amount of water it takes to fill them---which you’ll never do, btw---not to the number of jars they hold. Typically, the larger size processes seven to eight quarts, or twice that number of pints if they’re stacked.
     Purchase price should have no part of which size to choose. They actually are so close as to make no never mind. Amazon, for instance, recently had both sizes on sale, each for the same $79 and change.
     The determining factors should be how often you intend to use the canner, and the size of the load. I put a lot of food by, so the large size makes sense for me. But if you’re only going to do a couple of loads a year, maybe even mixing up the contents, than the smaller one might be a better choice for you.
     If you think you might use the canner as a pressure cooker as well, than the smaller size makes the most sense all around. However, if you do a lot of pressure cooking, you’re really better off getting an actual cooker, and buying a separate canner for putting foods by.

Control Mechanisms. As indicated above, pressure canners are controlled by a gauge, by a jiggler, or by a combination of both.
     Right off, forget about a gauge/jiggler combo. While the marketing hype (i.e., that they serve as checks on each other) makes them sound appealing, the reality is something else. The only thing they bring to the table is higher costs. There is no increase in performance or efficiency to justify that greater price tag. If you’ve got the money, spend it on additional lids, rings, and jars, rather than on a dual system. Let’s look at the single-controllers instead.
     -Gauges. Instinctively, most of us gravitate to a gauge, thinking it will be more precise. And until you understand how jigglers work, that’s probably true. There are two issues with gauges, however.

First, and foremost, is calibration. Most manufacturers recommend that you have the gauge calibrated before the first use, and once a year after that. Not too many years ago that wasn’t a problem. Hardware stores, cookware shops, and others were geared for doing that. Indeed, if nothing else, in the fall of the year, every Extension Service office in the country offered recalibration, either for free or for a very nominal fee. Those days are long gone, and it’s become more and more difficult to find anyone who can do the calibration. Which means, of course, that you don’t really know if the gauge is reading correctly or not.

Second: By their very nature, gauges are subject to small changes in the temperature source. You can’t just bring them up to pressure and let them be. Instead, there is a constant need for monitoring the reading, and fiddling with the heat source. The one thing you don’t need is radical changes in pressure, up and down. This will lead to boil-overs, and jars not sealing.

     A pound or so difference won’t matter much. But if you overpressure to, say, 12 pounds instead of ten, then drop it down to ten, and hope it won’t go to nine, then back up to 11, you will have problems. In fact, gauges are designed to work best at 11 psi, and if you go higher no big deal. Just don’t bounce up and down.

     -Jigglers. Once you understand them, jigglers are more practical than gauges, and, actually, more accurate.
I’ve never understood why the manufacturers don’t explain this, but a jiggler is nothing more than a pressure valve, pre-set to a specific psi. There are three “sizes” available: 5 pound, 10 pound, and 15 pound. You can also get a jiggler that combines all three controls in one unit.

In use, the jiggler is designed to release steam when the pressure reaches a certain point. The releasing steam, escaping around the jigglers, is what makes it rock back and forth. It jiggles, you see. Thus the name.

Heat source is all but irrelevant. The jiggler will always bounce around when the pre-set pressure is obtained. If you have the heat too high, all that means is that the jiggler will bounce harder and faster. In short, you cannot overpressure the unit with a jiggler properly in place.

In practical terms, you want to operate at the lowest heat setting that keeps the jiggler in movement. Two reasons for that: fuel consumption being one of them. The other: keep in mind you are venting steam continually. The faster the jiggler bounces, the more steam escapes. In theory, at least, you can have it going so fast that too much water evaporates, affecting proper operation.

It’s important that you get the correct jiggler. At sea level, about 95% of all foods are canned at 10 psi. So that’s the jiggler you should have. Just as with a boiling water bath, however, you do have to adjust for altitude. If you’re more than 1,000 feet above sea level, you’ll need the 15 psi jiggler instead. Processing time will remain the same.

Frankly, I don’t understand how the three-way jiggler works. Jiggler blanks start out at the same size and weight. Weight of the jiggler (and, thus, it’s release setting) is controlled by the depth of the holes that go over the nipple. I don’t see clearly how drilling three holes of different depths changes anything but the total weight.

Don’t get me wrong. I’m sure they do the job. But because I don’t understand how, I shun them. Jigglers are cheap enough, so that if you need more than one (a very rare occurrence), having separate ones is cost effective.

     -Storage. Pressure canners, particularly those using gauges, can be sensitive to knocking around. So you want to prevent that as much as possible.

It’s always a good idea to keep the original box, and store the unit in it. What I do is make sure the unit is completely dry. The owner’s manual and jiggler/knob both go inside the kettle. I then rest the lid, inverted, on the kettle. This goes into a plastic bag, the whole thing goes into the box, and the box put up out of the way until the next time it’s needed.

Next time we’ll walk step-by-step through the pressure canning process.

But we hae meat and we can eat
And sae the Lord be thanket
Back to Top
HistoricFoodie View Drop Down
Master Chef
Master Chef

Joined: 21 February 2012
Location: Kentucky
Status: Offline
Points: 4155
Post Options Post Options   Thanks (0) Thanks(0)   Quote HistoricFoodie Quote  Post ReplyReply Direct Link To This Post Posted: 12 December 2015 at 09:17

In many respects, boiling water baths and pressure canning are the same thing. They both use moist, high heat to destroy or retard the growth of pathogens. The jars are loaded the same. And so forth.

But, while the fundamental process is the same, there are some significant differences. For example, one surrounds the jars with water to provide the constant moist heat, the other surrounds them with super-heated steam.

What’s more, even among similar pressure canners, there can be differences. So be sure you read, and understand, the manufacturer’s instructions. This is especially true if you’ve chosen a smaller, 16-quart unit. My experience is entirely with the larger 22/23 quart units. So what I say may, or may not, apply.

For example, with the larger canners, you start with three quarts of water. I suspect that you use a lot less with the sixteens. But I don’t know that for sure.

One significant difference between boiling water baths and pressure canning is condition of the food product. With pressure canning, whenever feasible, you want to start with raw, or only partly cooked food. The reason is simple: You will, in effect, be cooking the food at 240F for as much as 90 minutes. There is always the danger, therefore, of overcooking the product. This, btw, is a quality issue, not a safety issue. But keep in mind that nobody likes to eat mushy meats and vegetables.

To reiterate, the following instructions apply, primarily, to 22/23 quart canners. And they assume that the unit is either new, or that you are using it the first time the season.

1. Prepare the canner. Check the gasket for cracks, breaks, or other damage. If you find any, replace it. Lightly oil the gasket if desired. If using a gauge, have it reliably calibrated. Make sure nothing is blocking the vent nipple (sometimes particles of food or debris get lodged in it.). A toothpick or small wooden skewer works perfectly for clearing the nipple.

2. Put the canner over a heat source. For the larger units, add three quarts of water. Some manufacturers recommend adding a tablespoon or two of vinegar, to help prevent scale buildup from minerals in the water. One of these days I’m going to try it.

3. Extra step: This is something I do that isn’t required. I fill the jars half- to two-thirds full with water and put them in the canner. There are two reasons for this. First is habit. I came into home canning when sterilizing the jars was still recommended. It’s a habit that’s hard to break. Secondly, it provides me a source of hot water for soaking the lids and rings, and for creating a holding bath for the filled jars. What I do is empty the first jar or two into a bowl holding the lids and rings. The rest goes into either the sink or a tub (depending on quantity of jars), as a holding bath.

4. Have the foodstuffs hot and ready to go. Loosely cover the canner, turn on the heat, and bring to a hard boil. You’ll know when it’s ready because there will be a strong column of steam coming from the vent. Lower the heat.

5. Fill the jars. Working with no more than two jars at a time, fill the jars, leaving an inch of headspace. That is not a typo! You need that much both to prevent boil-overs, and to have plenty of air to vent so that sealing of the jars is solid. Wipe the edges of the jar mouth with a damp towel, adjust the lids and rings, and stand the jars in a hot-water bath.
     Repeat with the rest of the jars.

6. Transfer jars to canner. Tightly cover. Bring to a hard boil, until steam escapes the vent in a strong, steady stream. Let the canner vent that way for a full ten minutes.
     Everyone is tempted to short-cut that step. But don’t do it. Venting as much air as possible, and filling the kettle with steam, is an important part of the process. Failure to do so could result in erroneous pressure readings, and possible unsafe food.

7. After venting a full ten minutes, put the jiggler or knob in place over the vent nipple. The pressure-lock plunger will almost immediately rise upwards and seal itself in place. Do not touch the plunger or try to adjust it from this point on.

8. Bring unit to desired pressure, adjusting heat as necessary to maintain it. Jigglers will operate, most often, at ten psi. Gauges should read 11 psi. Process for the time suggested by the recipe. This can range from as little as twenty minutes for pints of stock, to as much as 90 minutes (or more) for quarts of animal protein.

9. At the completion of the pressure time, turn off heat. Let the unit cool down on its own. Do not rush the process by removing the jiggler/knob or pressing down on the locking plunger. Cool-down time is part of the total processing time, and is important to food safely. In addition, if you rush it, the sudden decompression can cause boil-overs in which as much as half the jar contents will erupt into the canner. So have patience and wait for the unit to depressurize on its own.
     CAUTION! Even after depressurization, there is still a fair head of steam in the kettle. So open it carefully, with the cover facing away from you to deflect some of that steam, and for any condensation to drip back into the pot.

10. Remove the jars from the canner. Stand them in a draft free location. Many times the contents will continue to bubble for some time. That’s perfectly normal. Do not move the jars again until they’ve cooled enough for the lids to seal fully.
     “Fully” is the key word here. That bubbling you see is more air being forced out of the contents by the high heat. So you’ll sometimes have a situation where a jar seals with an audible pop. But the upward pressure of escaping air forces it to unseal. It then seals again. Sometimes the same jar will seal and unseal three or four times during this cooling process, until eventually sealing for good.

What about jars that don’t seal? In my experience, that actually happens less frequently with pressure canning than it does with boiling water baths. I’ve no idea why.

However, to salvage that jar as a shelf-safe product, you have to process it all over again. That means going through the whole process, start to finish. Personally, I’d never do that for just one jar.

You could include it as part of another canner load. But the question then, is, what happens to the food quality. It’s one thing to “recook” something like a clear stock. But what if the jar contains, say, venison chunks. Reprocess that jar and you’re guaranteed to have meat mush.

When I have an unsealed jar, I either use the contents immediately; store them in the fridge short term, or transfer them to the freezer.

But we hae meat and we can eat
And sae the Lord be thanket
Back to Top
Effigy View Drop Down

Joined: 17 June 2013
Location: New Zealand
Status: Offline
Points: 634
Post Options Post Options   Thanks (0) Thanks(0)   Quote Effigy Quote  Post ReplyReply Direct Link To This Post Posted: 13 December 2015 at 22:42

Clap  This is good stuff Brook. Thanks.
And Amazon WILL ship one to me if I decide I want to go down this road.
Resident Peasant
Back to Top
TasunkaWitko View Drop Down
Admin Group
Admin Group

Joined: 25 January 2010
Location: Chinook, MT
Status: Offline
Points: 7981
Post Options Post Options   Thanks (0) Thanks(0)   Quote TasunkaWitko Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2016 at 19:40
Brook - thank you for posting this. As you know from our private conversations, this goes right along with my goals for the coming year.

Reading and enjoying - and grateful....
If you are a visitor and like what you see, please click here and join the discussions in our community!
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

This page was generated in 0.063 seconds.