What Is a Pressure Canner?
Both pressures canning and boiling water bath canning include the processing of canning jars loaded with food in hot water; however, pressure canning is a significantly different way of preserving food than boiling water bath canning.
It is possible to safely preserve low-acid foods that, if canned in a boiling water bath, would pose a significant risk of foodborne illness (botulism, for example). Pressure canning eliminates this risk. In addition to that, you will need a pressure canner, which is a highly specialized piece of hardware (and should not be confused with a pressure cooker).
Before we get into the specifics of how to use a pressure canner, I want to make sure that you have a complete understanding of which foods must be processed in a pressure canner as opposed to a boiling water bath.
This will allow us to move on to the next step of learning how to use a pressure canner. It is possible to use a bath of boiling water to prepare foods that are acidic, defined as having a pH of 4.6 or below.
These foods include fruits and fruit preserves such as jam, as well as pickles and chutneys with a sufficient amount of vinegar in the recipe, tomatoes (which are technically a fruit) with added acid, and pickles and chutneys with a sufficient amount of vinegar in the recipe. In addition, tomatoes are technically a fruit.
However, if you wish to keep more alkaline items such as soup stocks, unpickled vegetables, or meat in sealed jars at room temperature, you will need to prepare these foods in a pressure canner first.
This is why:
Even if Clostridium botulinum and the toxin that it generates are destroyed when exposed to temperatures as high as boiling water, the spores of the bacterium can endure temperatures of this kind.
And do you have any idea what type of atmosphere they need in order to “hatch”? Somewhere with humidity and devoid of oxygen, which is precisely what they receive inside of jars that have been hermetically sealed.
A pressure canner has the ability to heat the food contained inside the jars to a temperature that is higher than the temperature of boiling water. This temperature is high enough to eradicate even the dormant spores of botulism.
Because of this, it is absolutely necessary to use a pressure canner when preserving foods with a low acid content.
Can You Explain What a Pressure Canner Is?
The bottom of a pressure canner is designed to resemble a huge metal pot, and it has a rack that can be removed and replaced inside the pot’s interior. The majority of the gear is located within the lid.
The lid of a modern pressure canner, which either screws on or is held in place with built-in clamps, has a steam vent (sometimes called a petcock) and either a weighted or a dial gauge that lets you know how many psig (pounds of pressure per square inch) have built up inside the canner.
The psig measurement is equivalent to the amount of force that would be exerted on an object if it were compressed to one square inch.
In contrast to some of their predecessors from the 20th century, current pressure canners are equipped with safety fuses that will blow off excess pressure far before it reaches a point where it may be harmful.
It is important to keep in mind that a pressure cooker and a pressure canner are not the same piece of equipment and thus cannot be used interchangeably, even if a pressure canner can also serve the purpose of a pressure cooker.
Canning using a Pressure Cooker: How to Do It
When preparing food for pressure canning, it is essential to leave a headspace of at least half an inch after filling the canning jars with the food. This is the case even when using the boiling water bath method. Before putting the canning lids on, make sure the rims of the jars are clean by wiping them down with a clean cloth.
Because the processing time for canning under pressure is always going to be more than ten minutes, it is important to note that sterilizing the jars is never going to be essential.
Put the rack that comes with your pressure canner inside the canner so that it is lying flat on the bottom. Add water. In contrast to a bath in boiling water, you won’t fill the jars all the way up with water with this method:
Check the instructions provided by the manufacturer to determine the exact quantity that should be used for your model.
Turn the heat up to high, then lock the lid of the pressure canner but be sure to leave the vent open. Sooner or later, steam will shoot out of the vent in a vigorous manner. When this occurs, you should prepare a timer for ten minutes.
Close the vent once the steam has been pouring out of it for ten minutes without interruption.
When using a weighted gauge, the vent is sealed up by covering it with the weight that comes with the gauge. The weight is divided into three compartments, each of which is labeled with a distinct level of pressure: 5, 10, or 15. Make sure to choose the hole that corresponds to the number of pounds of pressure that is indicated in either the 10 or the 15. Make sure you use the right opening for the number of pounds of pressure that the recipe calls for.
As soon as the pressure reaches that point, the gauge will start to wiggle and there will be sporadic releases of steam.
When using a dial gauge, all you need to do is read the pounds of pressure that are shown on the dial.
There are variants of pressure canners that come with both a weighted gauge and a dial gauge.
Once the pressure inside the canner has reached the level that you want it to be at, you should start timing for the number of minutes that are specified in the recipe.
Keep a close check on the pressure: If at any point it falls below the amount that is specified, you will need to put the pressure back up and begin timing again from the beginning.
Take the example of me canning soup stock according to the recipe, which asks for 20 minutes of processing time at 10 pounds of pressure. In contrast, after 15 minutes, I see that the pressure has decreased to 8 pounds.
After increasing the temperature and bringing the pressure back up to 10 pounds, I have to begin timing the complete 20 minutes from the beginning once again.
Once the allotted time for canning has passed, the heat should be turned off; however, the vent should not be opened and the lid of the pressure canner should not be removed just yet. Wait for the pressure within the canner to drop all the way down to zero, and then wait for an additional two minutes after that.
After the allotted amount of time has passed, proceed to first remove the lid, and then open the vent.
Make use of a jar lifter to transport the jars to a location where they will not be disturbed until they have reached their final cooling temperature (this can take several hours).
If the surface that you will be placing them on is going to be chilly, you should first set a rack or a dish towel there, and then put the jars on top of it: Jars made of glass that are brought into contact with a chilly countertop may shatter.
After being removed from the pressure canner, it is not uncommon for the contents of the jars to continue boiling furiously for a few minutes after the pressure has been released.
As the jars cool, the lids should transform from being flexible and convex to being rigid and concave, much as they do during the process of canning in a boiling water bath. Resist the temptation to check the jars’ lids before the food within has had a chance to totally cool:
If you pressed on them while they were still hot, a false seal may be created, which would indicate that a vacuum wasn’t completely generated before the lid snapped into the concave position.
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