Rolling up your sleeves to can your favorite jam or pickle recipe? Great! What about the jars? Do you need to sterilize them for canning? Maybe you’ve heard it’s not always necessary. Maybe you’ve heard some methods are better than others. Here’s the safest, most current information on when and how to sterilize jars. You may be a bit surprised with what you learn, in fact.
New jars straight from the box are not sterile. And the jars you ran through the dishwasher months ago and kept on a shelf in the basement likely aren’t sterile, either.
Luckily, sterilizing jars is simple, and there are a few methods you can choose from. The best way to sterilize jars will depend on how many jars you need. Technically we’re sanitizing the jars, not sterilizing the jars, but rather than get too persnickety on terminology, let’s get down to business.
Why Sterilize Jars?
Sterilizing jars will kill any undesirable bacteria that could make your canning project go awry. If you’re investing the time to preserve adorable foods in jars, the step of sterilizing those jars easily pays off in food safety, keeping quality, and pleasant flavor.
Is It Always Necessary to Sterilize Canning Jars?
Actually, no! Jars for canning recipes that are processed in a water bath for more than 10 minutes do not need to be sterilized. The heat from the prolonged time in the water bath does that job for you. Jars for any canning project will need to be freshly cleaned in hot, soapy water, however.
When canning, you do want your jars to be hot when you fill them with hot foods, such as jams and jellies (having the jars and the food you are putting in them at the same temperature keeps the glass from getting shocked and possibly cracking). Keep that in mind when you select your method.
Sterilizing Jars in the Oven
The reliability of sterilizing jars in the oven method is questionable, since many ovens don’t run true to temperature, and they don’t always hold that temperature consistently during an extended period. Canning jars are not made for dry heat, the way tempered glass like Pyrex is. Dry heat can weaken canning jars, making them more prone to breakage.
Sterilizing Jars in the Microwave
You may see posts online about sterilizing jars in the microwave, but we deeply caution against it. Microwave wattage varies greatly from model to model, making this method impossible to regulate. More importantly, microwaving wet and empty jars can be hazardous—they don’t heat evenly, can become dangerously superheated easily, and might even explode.
Neither the National Center for Food Preservation nor Newell (manufacturer of Ball and Kerr jars) endorse sterilizing jars in the oven or microwave, so we’re not recommending it, either.
Method 1: How to Sterilize Jars in the Dishwasher
For this method to be effective, you need to have a “sanitize” setting on your dishwasher. This setting heats the water to a minimum of 150°F, which is hotter than typical dishwasher settings.
- Put the jars you are sterilizing in the dishwasher with the openings facing down. It might sound obvious, but it’s fine if other dirty dishes from your regular life happen to be in there, too.
- Run the dishwasher in the sanitize cycle. Bear in mind that the sanitize cycle might run longer than typical wash cycles. Keep that in mind when planning your project.
- If you need to keep your jars hot for canning, keep them in the steamy dishwasher until it’s time to fill them.
Method 2: How to Sterilize Jars in a Water Bath
This method is very logical for water bath canning, since you’ll have a water bath going, anyway.
- Put the jars with the opening facing up in a large canner or stockpot on a canning rack. Fill with enough water to cover the jars by 1-inch (fill the pot with hot tap water to cut down on the time it takes for the pot to come to a boil.
- Cover the stockpot with a lid and boil for 10 minutes.
- Use jar lifters to lift the jars from the boiling water. Carefully empty the water back into the pot, then set the jar open-side-up on a clean kitchen towel to drain. Let the jars dry naturally (it should happen pretty quickly).
Altitude Adjustments for Sterilizing Jars
At elevations above 1,000 feet, water boils at a lower temperature—as low as 200°F—than the typical 212°F achieved at lower elevations. As a result, it's necessary to adjust the boiling time when sterilizing jars at higher altitudes to ensure heat-resistant bacteria are destroyed. Boil 1 extra minute for each additional 1,000 feet of elevation.
A Few Other Notes
- Avoid using any jars with cracks or chips.
- If you’re canning, use only jars made for canning. Reusing a jar that, say, once held store-bought prepared mustard is a noble idea, but that jar might not hold up very well to the canning process.
- What about lids? You don’t need to sterilize metal bands and lids for canning. In fact, boiling the lids can cause the seal to fail when canning. Wash them in warm, soapy water and you’ll be fine.