Beforehand: There are regional differences of canning and preserving. The whole bunch of recipes and specialities represent the variety. Meaning, the notations of preserving and canning don't indicate on the conservation procedure. Therefore a few generally descriptions: Preserving and canning is often used as a hypernym. The german word "einwecken" is even protected by trademark law. Preserving is known as a heating-in-a-vacuum-process (see also: The WECK preserving method). Whether the normal preserving process or the preserved sausage from you butcher - both are operating on that principle. You usually pickle fruits and vegetables in oil, vinegar or alcohol.
This kind of preserving is classical. At this, the filled jars (WECK jars always have a rubber ring, glass lid and clamps – twist off jars have a suitable cap) are put in a pot - closed. The topmost jar should be covered with three-quarter of water. Then you heat up the water until it's boiling. Now, the preserving time starts. After the required preserving time (it differs from size to shape), extract the jars from the pot and let them cool down. But don't put it on a cold surface! If they are cooled down, remove the clamps - if there are any. If the lid is still closed tightly, your preserving was successful.
This procedure is like preserving in a pot, but with the advantage of an own heating unit. So you have an own temperature- plus time-switch. You put the already filled jars into the kettle and fill in the water. The water should have the same temperature as your filled jars. Now, the temperature is adjust. With an older version of the kettle, you just put it on the stove. By reaching the required temperature, your preserving time depends on the preserved food.
You stack the jars as usual in your pressure cooker. Fill in some water. Depending on your preserved food, you set the ring on level 1 or 2. Your preserving time starts now. When time ends, take the pot from the stove. The pot has to open all by himself - don't hasten the process by interfering.
It's an unusual process to preserve food with a steam cooker. But otherwise, it's a very comfortable handling and very effective, too. Place the jars in the lowest grate of the steam cooker. It's very important that the jars don't touch each other. Because then, the steam isn't able to reach every single jar. You can use the temperature and time information as described in the recipe. After turning off the steam cooker, the jars should stay inside the cooker for about 30 - 60 minutes.
First of all, you need a 0.78 inch high pan. Fill it with hot water and place the jars in the pan. But the jars are not allowed to touch each other or the inside of the oven. Set the top and bottom heat to 175 degrees. The jars stay so long in the pan, until you can see little air bubbles inside the jar. If the food is out of fruits, you can turn off the oven now. Are the ingredients out of vegetables or meat, set the temperature to150 degrees for 90 more minutes. After that, you can turn off the oven, too.
This process is not really preserving but jarring. It's especially used for marmalades and jams. The fruits and it's juice are cooked with the appropriate amount of sugar until they began to jelly. The mass is filled into the jars and shut them tightly. Usually, you use screw lids for twist off jars. Partly, some jars are closed with cellophane.
For preserving groceries, which have parts of milk and cream in it, must have a temperature of 119 degrees. Normally, boiling water just gets to 100 degrees. This means, you need a pressure cooker. Otherwise, the milk gets sour and you can throw away your food. Somehow, it's still possible to preserve dairy products in the normal way and to cool them after the process. Although, there is not the longstanding keepability as with traditional preserved groceries, but still long enough.