How to sterilize jars: methods to sanitize jars for preserves

Sterilizing jars is essential for long and safe preservation of homemade preserves. So let's discover the different sanitizing methods and useful tips for a perfect result.

By Cookist

If you want to prepare preserves, whether they are jams, vegetables in oil or sauces, there is an indispensable operation to carry out; the sterilization of glass jars. It is a fundamental process to remove fungi and bacteria and to create safe and genuine products to be preserved for a long time. But how to sterilize the jars? There are several methods to best sanitize them: boiling in a pot, or using the dishwasher, the oven or the microwave oven. To avoid bacterial contamination of your preserves, it is obviously necessary to sterilize new caps and lids or replace the old ones, including the rubber gaskets, to guarantee the jars a perfect hermetic seal. So let’s see how to do it.

How to sterilize glass jars for preserves: from boiling in a pot to the microwave oven


Sanitizing glass jars for preserves is an operation that does not require much time and that must be carried out both on new jars and on those already used previously, this is essential to proceed in a healthy and safe way in the realization of our home preparations. Before starting the operation, make sure that the glass jars are intact, without chips or cracks, use new lids and change the rubber gaskets of the airtight containers as soon as they dry out or change color. The first thing to do is wash the glass jars with hot running water, taking care to wash all its parts, including rubber gaskets and lids. But let's see how to proceed with the different methods of sanitizing glass jars.

In the pot: for a traditional and effective sterilization also valid for full glass jars


The sterilization of glass jars in the pot is the most classic method to use, and it is the one that takes more time. Get a large pot with high sides and line it with a clean cotton cloth. Now insert the glass jars, with the opening facing up, and place the cotton cloth between the jars to prevent them from bumping together. Fill the pot with cold water and let it boil for 30 minutes, add also the lids after 20 minutes of boiling. After the necessary time, let it all cool and then drain them upside down, always placing them on a clean cotton cloth.

This procedure is also used to sterilize full jars, in the case of sauces, jams, fruit juices or short-cooked preserves, but not for vegetables in oil or pickles as oil and vinegar are already valid preservatives. To proceed with this sterilization, follow the instructions for the empty jars and let it boil for an hour. Once the fire is off, let the jars cool and let them cool upside down.

In the dishwasher: a practical sterilization method for jars and lids


The sterilization of the jars in the dishwasher is simple and practical as it allows the sanitization of jars and lids in a single step. You can choose two methods, the fastest is to insert jars and lids, select the high temperature wash and, once finished, remove them from the dishwasher and let them dry. Otherwise you can use this other procedure; put the jars and lids in the dishwasher always choosing the high temperature wash, run it for a few minutes, take them out and rinse them with vinegar. Then put the glass jars back in the dishwasher and run it for a few more minutes. Let them dry upside down on a clean cotton cloth. In both cases it is important that there are only jars and lids in the dishwasher, without other dishes.

In the oven: for fast and innovative sanitization


Sterilizing glass jars in the oven is a quick and easy method. Turn on the oven using a temperature between 100 degrees C and 130 degrees C; do not raise the temperature above as the glass jars could break. Put them in a baking pan, being careful not to let them touch each other, bake them for 5 minutes, turn off the oven and let them cool in the closed oven for 20 minutes, also adding the lids when the oven is still hot.

Sterilization in the microwave oven: ideal for jams


The microwave oven is also a quick solution to sterilize jars, but it cannot be used for caps, which will have to be blanched in the pot beforehand. This is why it is an ideal method for hot foods, such as jams; in this case, after filling the hot jar with the boiling product, it must then be cooled upside down. This will also sterilize the lid. But here's how to do it; put the jar in the microwave oven with a little water inside, turn it on for 2/3 minutes, or until it boils. Throw away the water and dry them upside down on a clean cotton cloth.

Useful tips and advices to prevent pathogens and food poisoning


The toxins of botulinum, as well as of other bacteria, can be inactivated with heat, but this procedure does not kill the botulinum spore, unless an industrial treatment is carried out that involves boiling at 100 degrees C for at least 8 hours. Let's now see some useful tips to prevent other pathogens and avoid food poisoning.

Use the jars immediately after sterilization, otherwise the sanitization will lose its effectiveness. Also remember to never put cold products in hot jars, otherwise they will shatter. Hot products, on the other hand, must be placed in hot jars; fill them almost completely leaving only 1/2 cm and close them immediately by fastening the cap and put them upside down to create the vacuum. For airtight jars, especially useful for vegetables in oil, press the product well and make sure it is covered by the oil to avoid the formation of mold and bacteria.

Check that the vacuum has been created; to do this, a distinction must be made: for jars with a cap (twist off closure) be careful that the lid does not have a central swelling. The central part must be flat, thanks to the effect of the vacuum; put a finger in the center of the cap and press, if the operation is successful you should not hear any click-clack. For airtight jars, unhook the closure and try to lift, if the cap resists, then the product is vacuum packed. This test will suffice, obviously without completely opening the jar.


Keep the jars in a cool and dry place and away from light, wait at least 1 month before opening the jars and consuming the preserves. Once opened, keep the jars in the refrigerator, tightly closed, and consume the product within a few days; for this reason, small jars of 250 grams are recommended, which allow faster consumption after opening.

For preserves and pickles make sure that the product is covered by the liquid after each use while, for jams, avoid creating air pockets inside the jar.

Lids and rubber gaskets should be changed each time they are used to ensure perfect closure.

Remember to always wash your hands and the utensils you will use, as well as wash the vegetables well and cook the meat or fish you want to store.

If you are unsure of the integrity of the product, throw it away.

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