How to Sterilize Canning Jars | Safe Methods for Food Preservation

To safely sterilize canning jars, place them upright on a rack in a boiling-water canner, cover with hot water, boil for 10 minutes at altitudes under 1,000 feet, and add 1 minute per additional 1,000 feet of elevation — but only if your recipe processes the food for 10 minutes or less.

One cracked jar or a lid that didn’t seal can ruin a season’s worth of garden produce. The good news is that sterilizing canning jars is straightforward when you follow the right method — and skip the ones that break jars or leave bacteria alive. The key is knowing when sterilization actually matters, which tool to use, and how altitude changes the timing.

Most home canners assume every batch needs pre-sterilized jars. That’s only half right. If your recipe processes the filled jars for 10 minutes or longer — common for vegetables, meats, and most tomatoes — the boiling-water bath itself sterilizes the jars during cooking. Pre-sterilization is required only for recipes with a process time under 10 minutes, like jams, jellies, and quick pickles.

The Only Approved Method: Boiling-Water Sterilization

The National Center for Home Food Preservation (NCHFP), which maintains the USDA’s official canning guidelines, approves one primary method for sterilizing empty jars: the boiling-water canner approach. It’s the standard because it’s predictable, effective, and safe for all jar sizes.

Here’s the exact procedure:

1. Wash jars in hot, soapy water and rinse thoroughly.
2. Place jars upright on the rack inside a boiling-water canner. Do not let them touch each other or the canner walls.
3. Fill the canner with hot tap water — not boiling water — until the jars are covered by at least 1 inch of water. Starting with boiling water can shatter glass from thermal shock.
4. Bring the water to a full rolling boil (212°F at sea level).
5. Start your timer once the water reaches a steady boil. Boil for 10 minutes at elevations below 1,000 feet. Add 1 minute of boiling time for every additional 1,000 feet of elevation above sea level.
6. Turn off the heat and keep jars in the hot water until you’re ready to fill them. Remove them one at a time with jar lifters, dumping the water back into the canner.

Once removed, fill each jar immediately with hot food and apply the lid and band. A jar that cools off before filling needs to be re-sterilized or held at 140°F or above to stay safe.

When You Can Skip Sterilization Entirely

This is the most common surprise for new canners. If your tested recipe processes filled jars in a boiling-water canner or pressure canner for 10 minutes or longer, pre-sterilizing the empty jars is unnecessary. The heat that cooks the food also kills any microorganisms on the jar surfaces. The same rule applies: wash the jars in hot soapy water and keep them hot until filling, but skip the 10-minute boil.

Recipes that fall into the “no pre-sterilization needed” group include most vegetable packs, meat and poultry, seafood, and tomato products. Always check the specific process time in a current USDA-approved recipe or extension service guide before deciding.

If you’re stockpiling supplies and need the right jars, our tested roundup of the best canning jars covers the models that hold up to repeated use.

Does the Dishwasher Sanitize Cycle Work?

The dishwasher’s “sanitize” cycle is conditionally accepted by the NCHFP, but only if the cycle reaches an internal temperature sufficient for sterilization — typically 150°F or higher for the full cycle duration. Run the jars through a complete sanitize cycle and leave them inside the closed dishwasher until you’re ready to fill them. The trapped steam keeps the jars hot and sterile.

The catch is that not all home dishwashers reach the required temperature, and some extension services (including the University of Maine) still recommend the boiling-water method as the only fully reliable option. If you use the dishwasher, verify your machine’s sanitize cycle specs and treat it as a backup, not the primary method.

Methods That Are Not Safe for Sterilization

Several popular shortcuts are officially unsafe and should never replace proper sterilization.

Oven Sterilization — Strictly Prohibited

All food safety authorities, including the jar manufacturer Bernardin, explicitly forbid sterilizing jars in an oven. Dry oven air transfers heat unevenly — glass is a poor conductor — so some spots never reach pathogen-killing temperatures while others experience thermal stress that causes breakage. The same risk applies to heating empty jars in an oven before filling. Never use an oven for sterilization, preheating, or processing.

Microwave Method — Not Approved

Microwaving a wet jar on high for 60 seconds is common online advice, but the University of Maine Cooperative Extension states this is not an approved sterilization method. Microwave heating is inconsistent, leaving cold spots where bacteria survive. Use it only for warming jars before filling, never for sterilization.

Vinegar Soak — Cleaning Only

Soaking jars in undiluted white vinegar removes hard-water mineral deposits and cloudy film, but it does not kill bacterial spores. The USDA’s Complete Guide to Home Canning lists vinegar treatment as a cleaning step only. Wash with soap and water first, then use the boiling-water method for actual sterilization.

Sterilization vs. Cleaning: What Each Step Does

Altitude Adjustments That Keep Food Safe

Water boils at lower temperatures at higher elevations, so the standard 10-minute boil at sea level is not enough in the mountains. For every 1,000 feet above sea level, add 1 full minute to the sterilization time. At 5,000 feet (common in Denver and the Front Range), boil for 15 minutes. At 7,000 feet (Santa Fe, much of Montana), boil for 17 minutes. Use a elevation-to-altitude chart from your local extension office to confirm your exact timing.

Lid and Band Rules

Metal lids with sealing compound cannot be sterilized in the same way as jars. Boil new lids in a separate pot of water for 10 minutes before using — do not microwave them or place them in the oven. Screw bands (the rings) only need a hot soapy wash; they do not contact the food and do not require sterilization. Replace any lid with a damaged sealing compound or one that has been used successfully before — they rarely seal a second time.

Final Sterilization Checklist

• Check the recipe’s process time first: Under 10 minutes → sterilize empty jars. 10 minutes or more → wash and keep hot, skip sterilization.
• Always use a boiling-water canner with a rack — never place jars directly on the pot bottom.
• Start with hot tap water (around 140°F), never boiling water.
• Time the boil from the moment of full rolling boil, not from when you turn on the heat.
• Adjust for your elevation: 1 extra minute per 1,000 feet above sea level.
• Keep jars hot until filling: Remove one at a time, fill immediately, apply lid.
• Never use oven heat for sterilization or preheating.
• Replace lids each use — buy only what you’ll use within one year.