How to Sterilize Glass Jars Correctly: 4 Foolproof Methods to Sterilize Preserve Jars

Homemade preserves are a traditional way to preserve the flavor of seasonal products and ensure a well-stocked pantry. However, one of the fundamental aspects of food safety is the correct sterilization of glass jars, better defined as sanitization. Only an industrial process can guarantee the destruction of all heat-resistant microbial forms: for example, for a treatment at 100 °C, even more than 5 or 6 hours could be necessary. Since within the home there is no access to the appropriate equipment called autoclaves – which make products purchased at the supermarket safe – other means are used to treat jars, pots, caps and lids, avoiding health risks.

You can resort to boiling in a pot, as well as sanitizing in the oven, in the microwave and even in the dishwasher: you should never underestimate this crucial step, because it allows you to preserve foods (from jams to pickles) for long periods, reducing the initial possibility of mold formation and reducing the risk of poisoning, even serious ones: it should be specified that the sterilization of empty jars does not eliminate botulism, since this forms in foods, but it serves to thoroughly clean the container, starting from a sanitized environment.

The general advice is to use the jars as soon as they are sterilized, so as not to ruin the operation. Also, be careful of thermal shock with consequent breakage or cracking of the glass: if you have to pour hot preserves, in fact, the jar must not cool completely. In addition, make sure that the vacuum has been created (the classic twist off caps must not make a clicking sound if pressed in the center after being closed) and store in a cool, dry place, away from direct sources of light and heat. Don't forget: in this case recycling is prohibited, but always get new containers, seals and jars.

1. How to Sterilize Glass Jars in Boiling Water

This is sanitization by boiling, and it is one of the most reliable techniques for preparing glass jars to be filled. This method uses the heat of boiling water to kill microorganisms present on jars and lids. How to do it? Get a large pot with high edges and cover it with a clean cloth in which you will wrap the jars, which will not touch each other with the possibility of breaking. Place them empty, with the opening facing upwards. Fill the pot submerging them completely and once the water boils, let it boil for 30 minutes: after 20 also add the lids. Transfer them with tongs to a clean cloth: never touch the inside with your hands.

You can do the same with jars filled with cooked preserves: after creating the vacuum, boil them for at least 10 minutes and then leave them to cool upside down.

2. How to Sterilize Glass Jars in The Oven

This is a very practical alternative variant, especially when you need to sterilize a larger quantity of jars at the same time and in less time. Set the oven temperature between 200°F and 266°F (or 100 °C and 130 °C), no more, to avoid breakages. Immediately place the jars on the oven rack and also position the lids without direct contact with the glass. Close and leave the jars for 5 minutes: at this point turn off, but without opening the door and let them cool inside for another 20 minutes.

3. How to Sterilize Glass Jars in The Dishwasher

Sterilizing jars in the dishwasher can be a convenient option, but not all cycles are suitable: you will have to choose a high-temperature program, the hottest available (usually reaching 158-167°F or 70-75 °C). Doing it is very simple: place the jars upside down and the lids in the appliance, taking care to place them separately so that they do not touch each other. Once the cycle is finished, leave them inside until you use them, making sure they are well dried: obviously there must not be any other dishes inside. Use it for preserves with a low risk of contamination, which contain high quantities of sugar, salt or vinegar, elements that naturally inhibit bacterial proliferation.

4. How to Sterilize Glass Jars in The Microwave

Sterilization in the microwave is a quick option, ideal when you have small jars, although the non-uniform heat propagated in the microwave might make this option unsafe. It is also important to note that this method is only suitable for jars without metal parts, so you cannot use classic lids in this process. How to proceed? Place the jar in the microwave with a little water inside – a little less than half – turn it on for 2/3 minutes, or until boiling. Empty it and let it dry upside down on a clean cloth. The lids must be sanitized separately by boiling in a pan: for this reason it can be used for jams, marmalades and sauces, where the vacuum is then created: the suggestion is to choose it only for short-term preserves.