How to Sterilize Canning Jars: When You Actually Need To, and the 10-Minute Rule

Here is the short answer most people are looking for when they ask how to sterilize canning jars: you probably do not need to. The National Center for Home Food Preservation limits the requirement to one narrow category, and if your recipe falls outside it, you have been boiling empty glass for no reason.

That said, the batches that do need it really do need it, and the method has two details that get fumbled constantly. So let's go through when it matters, exactly how to do it, and the one substitution that lets you skip the step honestly rather than by guessing.

Do you need to sterilize canning jars?

Only for short processing times. NCHFP's rule is that sterilizing is required for "all jams, jellies, and pickled products processed less than 10 minutes."

Everything else is off the hook. NCHFP states that "empty jars used for vegetables, meats, and fruits to be processed in a pressure canner need not be presterilized," and the same goes for "fruits, tomatoes, and pickled or fermented foods that will be processed 10 minutes or longer in a boiling-water canner."

The reasoning is the part that makes it stick. As NCHFP puts it, "When a process time is 10 minutes or more, the jars will be sterilized DURING processing in the canner." The canner does the job while the food is in there. Pre-sterilizing in that case is not a safety margin, it is a second run of the same cycle.

So the test is one question: what is my process time? Under 10 minutes, sterilize. Ten minutes or more, do not bother.

How do you sterilize canning jars, step by step?

You boil them in the canner you are about to use, in water that starts hot rather than boiling. Here is NCHFP's method with nothing added.

1. Wash and inspect. Wash jars in a dishwasher or by hand with detergent and rinse well. Then run a fingertip around every rim. A nick, chip, or hairline crack means that jar is out of the rotation for canning.

2. Load them upright. Put the empty jars right side up on the rack in a boiling-water canner. Right side up, not inverted.

3. Fill with hot water, not boiling. "Fill the canner and jars with hot (not boiling) water to 1 inch above the tops of the jars." Both the canner and the jars, so the glass is surrounded and filled at the same temperature.

4. Boil 10 minutes, then adjust for altitude. Boil 10 minutes at elevations below 1,000 feet. Add 1 additional minute for each additional 1,000 feet of elevation.

5. Pull them one at a time. "Remove and drain hot sterilized jars one at a time. Save the hot water for processing filled jars." Fill each jar as you pull it, rather than lining them all up on the counter to cool while you work.

Two of those steps are where people go wrong, so they are worth a second pass.

Why does the water start hot instead of boiling?

Because glass does not like sudden temperature changes. Dropping a room-temperature jar into boiling water is thermal shock, and thermal shock is how jars crack in the canner instead of in the trash. Starting with hot water and bringing the whole pot up together lets the glass and the water climb at the same rate.

That is also why step 5 says one at a time. A sterilized jar sitting empty on a cool counter for 10 minutes is no longer hot, and pouring hot jam into a cooled jar reintroduces the same shock from the other direction.

What is the altitude adjustment for sterilizing jars?

Add 1 minute per 1,000 feet above 1,000 feet. Water boils at a lower temperature as elevation rises, so a boil at 5,000 feet is simply not as hot as a boil at sea level, and it needs more time to do the same work.

Run the numbers for where you live once and write them on the inside of a cabinet door:

If you do not know your elevation, look it up now rather than in the middle of a batch. This is the single most commonly skipped adjustment in home canning, and it applies to processing times too, not just to sterilizing.

The shortcut that lets you skip sterilizing entirely

This is the part most guides leave out, and it is straight from NCHFP: you can "increase a 5-minute process time for certain jams and jellies to 10 minutes so that they do not have to pre-sterilize the jars."

Think about what that trades. Instead of boiling empty jars for 10 minutes and then processing the filled jars for 5, you skip the first step and process the filled jars for 10. Same total time at the stove, one less pot to manage, one less window where a sterilized jar sits around getting cold.

The honest caveat: a longer boiling water process is slightly harder on delicate set and color in a soft jam. If a bright, barely set berry jam is the whole point of the batch, pre-sterilize and keep the short process. For everything else, the longer process is the simpler path.

Do canning lids need to be sterilized or boiled?

Follow the box. NCHFP's instruction on lids is deliberately deferential: "Carefully follow the manufacturer's directions in preparing lids for use." Lid sealing compounds have changed over the years, and the old habit of simmering lids in a pan is no longer what every manufacturer calls for.

What has not changed is inspection. NCHFP says to "examine all metal lids carefully" and warns: "Do not use old, dented, or deformed lids, or lids with gaps or other defects." It also notes lids perform best within 5 years of manufacture, which is a good reason to buy lids in the amounts you will actually use in a season rather than stockpiling a decade of them.

Two more lid rules worth tattooing on the inside of the pantry door. First, "Do not retighten lids after processing jars," because air escaping and the vacuum forming are exactly what you want and retightening interferes. Second, screw bands come off once the jars are cool, and they can be reused. Leaving bands on stored jars makes them difficult to remove later and invites rust.

Can you sterilize canning jars in the dishwasher or the oven?

The dishwasher washes, it does not replace the boil. NCHFP's guidance uses the dishwasher for cleaning ("Wash jars in a dishwasher or by hand, using detergent and rinsing well") and as a way to hold jars warm, noting you can leave them in the closed dishwasher after the cycle. That is a genuinely useful trick on a busy canning day, because warm jars are the goal even when sterile jars are not required.

For sterilizing where sterilizing is required, though, the method NCHFP publishes is the 10-minute boil in the canner. That is the one to follow. Dry heat in an oven is not part of any current recommendation, and glass under dry heat is a risk you are taking for no documented benefit.

Which jars are safe to sterilize and reuse?

Mason-type canning jars, in sizes from half pint through half gallon, are what the recommendations are written around. NCHFP also allows that "most commercial pint- and quart-size mayonnaise or salad dressing jars may be used with new two-piece lids" for acid foods, while being straight about the tradeoff: expect more seal failures and more breakage. It does not recommend them for pressure canning at all, because of excessive breakage.

My own practice: commercial jars hold dry goods and refrigerator pickles. Real canning jars do the canning. The price difference over a season is small, and a jar that breaks in the canner costs you the jar, the food, and the afternoon.

A canning-day order of operations

• Look up the process time for your recipe first, because that one number decides whether you sterilize.

• Wash jars, inspect rims, and set aside anything chipped.

• If the process is under 10 minutes, sterilize per the 5 steps above. If not, just keep the jars clean and hot.

• Prepare lids per the manufacturer's directions and inspect each one.

• Fill hot jars one at a time, process, and do not retighten the lids afterward.

• Remove bands once cool, wipe the jars, label with contents and date.

Frequently asked questions about sterilizing canning jars

How long do you boil canning jars to sterilize them?

Ten minutes at elevations below 1,000 feet, with 1 additional minute for each additional 1,000 feet of elevation. Put the empty jars upright on the canner rack and fill both the canner and the jars with hot, not boiling, water to 1 inch above the jar tops before you start timing.

Do I need to sterilize jars if the recipe is processed 10 minutes or more?

No. NCHFP states that when a process time is 10 minutes or more, the jars are sterilized during processing in the canner. Pre-sterilizing in that case repeats work the canner is already doing. The jars still need to be clean and hot.

Can I sterilize canning jars in the dishwasher?

Use the dishwasher to wash the jars and to hold them warm, not to sterilize them. NCHFP's guidance is to wash jars in a dishwasher or by hand with detergent and rinse well, and you can leave them in the closed dishwasher after the cycle to keep them hot. Where sterilizing is actually required, the published method is the 10-minute boil in the canner.

Why should the water be hot and not boiling when the jars go in?

To avoid thermal shock. Glass cracks when its temperature changes fast, so starting with hot water and bringing the pot to a boil with the jars already in it lets the glass and the water rise together. The same logic is why you fill each sterilized jar as you pull it out instead of letting it cool on the counter.

Do canning lids need to be boiled before use?

Follow the manufacturer's directions, which is exactly what NCHFP advises, because lid compounds differ and the old habit of simmering lids is not universally called for anymore. What is universal: examine every metal lid and do not use old, dented, or deformed lids, or lids with gaps or other defects. Lids work best within 5 years of manufacture, and you never retighten lids after processing.

Can I reuse canning jars and screw bands?

Jars and bands yes, flat lids no. Bands can be removed once the jars have cooled and reused, and NCHFP notes that leaving them on stored jars makes them hard to remove and prone to rust. Inspect jars for nicks before every use, since a damaged rim is the most common reason a seal fails.

One number decides the whole question, and it is the process time on your recipe. Learn to look for that first, and jar prep stops being a ritual and becomes a two-second decision.

You never know, but you can always be ready.

Sources: National Center for Home Food Preservation, Sterilization of Empty Jars · NCHFP, Do I need to pre-sterilize my jars before canning? · NCHFP, Recommended Jars and Lids