What's
pressure canning?
Pressure canning is the best method for safely preserving food. "Safe" means that you kill all harmful bacteria during the canning process, including botulism. Because canning kills these harmful bacteria, you can keep the food you preserve this way for at least a year. Simply on the shelf instead of in a freezer.
Pressure canning uses a special pot, the pressure canner. A pressure canner is similar to a pressure cooker, although there's one important difference: with a pressure canner, you can read the pressure inside the canner. This pressure information is essential for safe canning.
If you want to preserve foods with a low acidity, such as vegetables, meat and fish , pressure canning is the only safe method.
Good to know before you start is that there are a few things you can't can:
- Grains, pasta, rice and tofu
- Pureed products such as potatoes, pumpkin, zucchini, and parsnips. These can be canned in cubes.
- Dairy products, eggs and coconut milk
- It is not recommended to pressure can cabbage, eggplant, lettuce, olives and artichokes.
You place the jars containing the food you want to preserve in the pressure canner. Because a pressure canner uses steam , the jars don't need to be largely submerged (as is the case with canning). Then you close the canner. The canner comes with a pressure weight, which is designed to close the steam valve. You place the pan on the stove, and the heat fills the canner with steam from the inside out. This pushes all the air out of the canner. When you place the weight, the pressure in the canner increases, and the temperature rises to over 115 degrees Celsius. This temperature is necessary to kill all bacteria .
When the jars cool after pressure canning, they automatically create a vacuum . This works like this: during heating, the contents of the jar expand, forcing all the oxygen out of the jar. As the jar cools, the contents shrink again, pulling the lid down and creating a vacuum. This seals the jar airtight, preserving your preserved food.
How works
pressure
canning?
Botulism and
preserve
Was ist Botulismus und warum ist er gefährlich?
Of all the harmful bacteria known, botulism is often discussed in connection with food. This is not without reason. The bacterium with the charming name "Clostridium Botulinum" can cause paralysis and even death. The most common form is foodborne botulism.
This occurs when food becomes contaminated with the bacteria and is then not preserved safely.
The bacteria that cause botulism poisoning are generally harmless to humans and animals. After all, they are ubiquitous in soil and water. The problem arises when the bacteria are exposed to certain conditions, when they produce toxins. These toxins are harmful.
When is there a risk of botulism?
Botulism bacteria, like most bacteria, die at around 100 degrees Celsius. The danger lies in the spores of botulism bacteria, which only kill at higher temperatures (115 degrees Celsius). These spores thrive in conditions with little oxygen, moisture, and low acidity. Exactly the same conditions as in a vacuum-sealed jar of vegetables. If you don't preserve them properly, the spores survive and multiply as soon as you open the jar.
Pressure canning involves cooking under pressure. This raises the temperature to a level that kills all bacteria, including botulism spores. It also neutralizes the toxins from the botulism bacteria. So, for example, if you've preserved a jar of beets in your pressure canner and open it after a year, you can use it straight away for a salad. You don't have to cook it again before it's safe to eat.
This is different from canning vegetables. When you open your jar after a year, you still have to cook the food for at least 10 minutes to render the toxins and spores harmless. And even then, you haven't killed all the bacteria and spores.
Pressure: the pressure gauge and the pressure weight
When the lid is on the pressure canner, the canner is completely closed. When the water starts to boil, the canner fills with steam. This causes the pressure in the canner to increase. This in turn causes the temperature in the canner to rise to above 115 degrees. And at that temperature all bacteria are killed. The amount of pressure you need to build up to be able to pressure can something safely varies a bit at what altitude you live.
If you want to achieve the correct temperature within your pressure canner, you must take into account where you live in relation to sea level. Water boils at a lower temperature as you go up. A lower cooking temperature is not effective enough to kill most bacteria.
The Netherlands
The minimum pressure you need in the Netherlands to can can safely when you work with a canner with a pressure weight is 10 PSI. If you work with a canner with a pressure gauge, it is recommended to work with 11 PSI.
The CanMate has both so you can safely preserve at 10 PSI.
Outside The Netherlands
If you live in a place higher than 300m above NAP (= New Amsterdam Level or sea level), it is important that you work with the pressure required for the altitude where you live. Below you will find a table showing which pressure to use. For example, if you live at 800 meters, you must increase the pressure in your canner to 15 PSI if you have a canner with a pressure weight and to 12 PSI if you have a pressure gauge. The CanMate has both so you can safely preserve at a pressure of 12 PSI.
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Pressure
Canners with a pressure weight and/or a pressure gauge
There are two different types of pressure canners:
-
the canners with only a pressure weight (weighted gauge)
-
and the canners with a pressure weight and a pressure gauge (dial gauge)
A canner with only a pressure weight works with a small weight attached to the canner's valve. The weight vibrates at the correct pressure. If your canner only uses a pressure weight and has a 10 psi weight, this weight will vibrate and hiss at 10 psi. If your canner has a 15 psi weight, it will vibrate and hiss at 15 psi.
Your altitude relative to sea level determines which weight you should use. As soon as the weight starts vibrating and hissing, you know your pressure canner is at the correct pressure and you can start the timer.
Our CanMate has a pressure gauge (dial gauge) that displays the pressure inside the canner. It's important to have the gauge calibrated annually to ensure accurate pressure readings. Several companies offer this service, and you can search Google to find a company near you that offers it.
Our CanMate Presspan 22 qt is equipped with both a pressure gauge and a pressure weight. Our latest version comes with a pressure weight for 10 and 15 PSI.
The advantage of having a pressure weight is that you don't really need to calibrate the pressure gauge every year. You simply wait until the weight starts hissing and turning. Then you know immediately that the correct pressure has been reached. An added benefit of a pressure weight is that you can hear it hissing even when you're a bit further away. So you don't have to constantly check the gauge.
Get going
When you're pressure canning, you first choose your recipe. You can use tested recipes from the USDA. This is the U.S. Department of Agriculture, which also handles food safety. Here's the link to the recipes:
Of course in English and they work with American sizes
There's also a very good Dutch alternative. If you'd like recipes for pressure canning translated into Dutch and using Dutch measurements and quantities, you can go to Boerderij in een Rijtjeshuis (Farmhouse in a Terraced House). It costs 5 euros.
Step-by-step
pressure canning
01
After you have chosen your recipe, you can get started. Make sure your pots are clean. It is not necessary to sterilize first because this is done during pressure canning.
Clean pots
02
Fill the jars
Get your jars ready to be filled. It is most convenient to do this with a funnel with a large hole. This ensures that the edges remain clean. Leave the recommended space at the top of the pot. If all goes well, this should be in your recipe. On average, that is 2.5 centimeters.
03
Then stir the jar with a chopstick. This will remove any air bubbles. It's important to remove as many air bubbles as possible from the jar. Air can cause your product to slowly spoil in the jar. That's why we want to remove as many air bubbles as possible. During pressure canning, the remaining air is automatically pushed out of the jar.
Remove air bubbles
04
Screw the lid on
Next, thoroughly clean the rims of your jar. If you used a good funnel, you'll hardly need to clean. If you're working with food that isn't greasy or sticky, a clean dishcloth with water is often sufficient. If you're working with greasy or sticky food, vinegar can be a good way to degrease the rim. Take a clean dishcloth, put some vinegar on it, and then run it along the rim.
It's crucial that the rim is clean, otherwise the lid won't adhere to the glass rim. Tighten the lid until it's finger-tight, but not super tight. If you tighten it too tightly, any remaining air won't be able to escape during pressure canning. This will leave air trapped in your jar, which you don't want.
05
When your jars are ready to preserve, fill the canner with 3 liters of water. It doesn't matter how many jars you have, there should always be 3 liters of water. Note: if your jars are hot, add hot water to the canner. If your jars are cold, add cold water. Then place your jars in the canner.
Double-check that the ring in your lid is properly positioned and place the lid on the canner, without the weight. Turn your heat up to high and wait until you hear/see steam coming from the valve. The time this takes varies depending on your stovetop and whether you started with cold or hot jars. Once the valve is switched on (and the pin in the right handle of the CanMate has popped up), lower the heat slightly. You want to avoid losing too much moisture from the canner, which could cause it to boil dry.
Fill the canner
06
Steam for 10 minutes and place a weight
Then set your kitchen timer for 10 minutes. During those 10 minutes, the canner fills completely with steam and pushes the air out. After 10 minutes you can place your weight on the valve and the pressure can slowly build up.
07
If you're using a canner with a pressure gauge, keep a close eye on the gauge until it reads the correct pressure for you. If you're using a canner with a pressure weight, wait until the weight vibrates. Once you've reached the correct pressure, start the timer for the desired canning time. You should be able to find this time in the recipe. You should only start the timer once the correct pressure has been reached.
Building pressure
08
Cool and empty
Once the timer goes off, remove your canner from the stove and let it release all the pressure. If your canner has a pressure gauge, you'll know when the gauge reaches zero. If you have a canner with only a pressure weight, the pressure has been released when you no longer hear any hissing.
Now you can remove the weight. Wait another 10 minutes before removing the lid. Then wait another 10 minutes and remove the jars from the canner using jar tongs.
You want to cool the jars gradually enough so that you don't expose them to a large temperature difference. The contents of the jars are still very hot, and when they get that hot, they expand. If the area around the jar suddenly becomes much colder when you quickly remove it from the canner, the hot contents will try to push out. This causes moisture to escape from your jars, and some can get trapped between the rim and the lid, potentially disrupting the vacuum seal.
So let your canner cool down slowly and wait 10 minutes between each step to prevent cooling too quickly.
Even if you're very careful, you might lose some of the contents of your jar. As long as more than two-thirds of the contents remain in the jar and the vacuum seal is sealed, you can still store it in the pantry. If you lose more, it's important to refrigerate the jar after it cools and eat it first, even after the vacuum seal is sealed.
09
Let your jars cool completely for 24 hours and then check if they're properly vacuum sealed. If you're using mason jars, remove the ring and check if the lid stays on securely. You can lift it by the lid, for example. If it stays on, the vacuum is strong enough.
If you work with reusable screw-on jars, you can check whether the cap has been sucked in and whether it no longer makes a noise when you press on it.
If you work with preserving jars, you can check whether the lid stays in place when you lift it by the lid without the bracket or clamps.
If your vacuum test was successful, the jar can go into the pantry. It's recommended to eat the contents of the jar within a year.
Pantry
Pressure can times
