How to Sterilize Jars in the Oven Step by Step

Canning is a great way to preserve food for a long time; however, the jars must be properly cleaned and sterilized to prevent bacteria from invading your new jars of canned food and spoiling it.

sterilizing jars in oven collage

A good glass jar can be reused over and over again if it has been properly sterilized before being used.

There are three ways to sterilize jars for canning:

  1. In the oven
  2. In the microwave
  3. In the dishwasher

A microwave and a dishwasher super-heat glass making them very effective tools for sterilizing jars. However, not everyone owns a microwave or dishwasher.

Thankfully, your oven can be used to sterilize your jars as well. Here is how to do it, step by step.

Why Sterilize?

There are 3 reasons to sterilize your jars:

  • Mesophilic microorganisms will be on the jars if they have not been subjected to high temperatures. These microorganisms will contaminate the food as it is trapped inside the jar.
  • If the jar is not hot when you can your food, thermophilic spores caused by thermoanaerobacter and thermoanaerobacterium can germinate and grow. It’s therefore important to jar and seal while both the food and the jar are piping hot.
  • Sterilization removes the bacteria, yeasts, and fungi present in the air and on surfaces that will cause spoilage.

All of these will spoil your food and cause food poisoning.

When to Sterilize

Sterilizing your jars needs to be part of your canning routine with your eye on the clock. Because bacteria are the problem when combined with food, you cannot sterilize your jars and then leave them on the counter for any amount of time.

You need to start by preparing your food and then begin to sterilize the jars about 20 minutes before the food will be ready to can.

Give yourself 10 minutes to prepare everything you need. You’ll need 10 minutes to wash the jars and set them on trays in the oven and then 20 minutes in the oven sterilizing.

sterilized canning jars on tray
Sterilize your jars when your food is almost ready for canning.

It is Now Time to Sterilize Your Jars

Before you start, make sure there are no cracks or chips in the jars before sterilizing them. Discard any that show any signs of damage.

Step 1. Prepare Your Fruit, Vegetables, Jam, or Meat

When you are canning, you need both the food and the jars to be ready at the same time. Work on your food first and time your sterilization for when the food will be ready.

Step 2. Preheat the Oven

Preheat the oven to 320 – 350 degrees Fahrenheit (160 – 180 degrees Celsius) for 15 minutes while you prepare your jars.

Step 3. Wash

Wash your jars in hot soapy water.

washing canning jars in soapy water

Step 4. Rinse

Rinse the soap off of the jars in hot water. You need the jars to be hot before going into the oven to prevent damage to the glass.

canning jars inside oven

Step 5. Place on Oven Tray

Without drying the jars, place them upside down on an oven, roasting, or baking tray. They need to be wet going in.

Step 6. Heat the Jars

Place the trays in the hot oven, close the oven door, and leave them for 20 minutes. If your food is not ready, you can leave the jars in the oven until you are ready to ladle the food in.

You cannot use cold jars because they may crack when filled with boiling hot food and, while they have been sitting cold, bacteria could move in.

sliced beets boiling on stovetop next to pot with canning lids

Step 7. Sterilizing Seals, Lids, and Lid Inserts

In South Africa, we have three options for canning jars: we have one that has an insert lid, another that has a fixed replaceable lid, and a third that has a glass lid fitted with a rubber seal.

For the lid with the insert, the insert can only be used once and must then be thrown away (replacements are available in stores).

For the jar with the fixed lid, the lid can only be used once and must then be thrown away (replacements are available in stores).

Neither jar with a discardable lid has a rubber seal.

For the jar with the glass lid, the rubber seal must be sterilized on the stovetop and the glass lid must be sterilized in the oven with the jar.

Inserts, lids, and rubber seals must all be sterilized separately from the jars in boiling water on the stove.

Remove the seals from the lids and boil all parts of the lids in a pot on the stovetop for 2 – 3 minutes. As with the jars, you can leave them in the hot water until you are ready with your food.

Leave the lids for last as they do not take long to prepare.

canning lids on boiling water on stove
Sterilize the lids in boiling water on the stovetop for 2 – 3 minutes.

Step 8. Can Immediately

Once your jars have been in the hot oven for 20 minutes, remove them from the oven and immediately ladle out your hot food into the jars while both the food and the jars are hot.

Immediately seal the jars trapping all the goodness inside and all those harmful germs and bacteria out.

Step 9. Cool

Cool your jars of canned food immediately upon canning by placing the filled jars in boiling hot water and allowing them to simmer on the stove.

Remove from the heat and leave your canned goods in the hot water to cool off gradually.

This will protect your jars from the sudden change in temperatures and it will kill off any bacteria on the outside of the jars.


When should I start to sterilize my jars?

Time your canning so that you start preparing and sterilizing your jars 35 minutes before your food is ready.

How many jars should I sterilize?

Sterilize a few extra jars (I do 2 spares) than you think you will need in case you have more food than you thought you would have.

What will happen if I do not sterilize the jars before canning?

If you do not sterilize the jars before canning your food will be contaminated by bacteria, fungi, or yeast. Contaminated food can cause serious illnesses.

Do all canning recipes require jar sterilization?

Recipes that require a water bath lasting more than 10 minutes may not require that the jars need to be sterilized before canning.

Do I need to sterilize newly purchased jars?

If it’s a new purchase, you absolutely must sterilize the jars. Jars in stores have been in trucks and warehouses, and have been handled by many people. They are a haven for fungi, yeast, and bacteria and must therefore be properly sterilized before used.

Happy canning y’all.

sterilize jars in the oven pinterest

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