Do you need to sterilize jars before canning jam?
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You need to sterilize jars only when the jam will be processed for less than 10 minutes, which in practice means USDA and NCHFP recipes with a 5 minute time at low elevation. Any process of 10 minutes or more sterilizes the jars while it runs [1]. To sterilize, boil the clean, empty jars covered by an inch of water for 10 minutes, plus 1 minute for each additional 1,000 feet of elevation [1]. Dishwashers and ovens do not sterilize jars. This page shows when sterilizing is required, how to do it at your elevation, and when it is worth doing even though you could skip it.
The 10 minute line
The rule comes from the National Center for Home Food Preservation (NCHFP). Jars must sit under boiling water for 10 minutes to be sterilized. When a recipe's processing time is 10 minutes or more, "the jars will be sterilized DURING processing," so a separate step adds nothing [1]. UC Master Food Preservers give the same rule: pre-sterilize "only when the processing time is less than 10 minutes" [2].
| Your recipe's processing time | Sterilize first? | Why |
|---|---|---|
| 5 minutes (USDA jam and jelly recipes at 0 to 1,000 ft) | Yes | The process is too short to sterilize the jars [1][3] |
| 10 minutes or more | No | The process sterilizes them [1] |
| 5 minutes, but you would rather not sterilize | No, if you lengthen the process | Use the 10 minute unsterilized-jar time plus your altitude adjustment instead [1] |
That third row is why there are two sets of jam processing times. Guide 7, USDA's jam and jelly chapter, specifies "pre-sterilized Mason canning jars, self-sealing two-piece lids, and a 5-minute process" [3]. NCHFP notes that some people raise that 5 minute time to 10 minutes, "plus any altitude adjustments," so they can skip sterilizing [1]. Both routes are tested. The full charts for each, by elevation, are on how long to process jam.
At 1,001 feet and above, USDA's own jam time is already 10 minutes or more [3], so above 1,000 feet you will rarely need to sterilize unless you have a reason to choose the shorter sterilized-jar row.
How to sterilize jars
This is NCHFP's method [1].
- Wash the jars in a dishwasher or by hand with detergent, and rinse well. Check each rim for chips and nicks as you go.
- Set the jars upright on the rack in your boiling water canner.
- Fill the jars and the canner with water to 1 inch above the jar tops.
- Bring to a boil and boil for the time in the table below. Start timing when the water boils.
- Lift the jars out one at a time and pour the water from each back into the canner. That keeps the canner water hot and ready for processing the filled jars.
- Fill the jars while they are still hot. If they have to wait, keep them in the hot canner water.
| Elevation | Boil empty jars for |
|---|---|
| Up to 1,000 ft | 10 minutes |
| 1,001 to 2,000 ft | 11 minutes |
| 2,001 to 3,000 ft | 12 minutes |
| 3,001 to 4,000 ft | 13 minutes |
| 4,001 to 5,000 ft | 14 minutes |
| 5,001 to 6,000 ft | 15 minutes |
| 6,001 to 7,000 ft | 16 minutes |
| 7,001 to 8,000 ft | 17 minutes |
The table applies NCHFP's 10 minutes plus 1 minute per additional 1,000 feet [1], rounding any part of 1,000 feet up to the next minute. UGA's jam bulletin gives the same rule for sterilizing [4]. If you don't know your elevation, how altitude changes jam making shows how to find it.
Lids are not sterilized. Prepare them the way the lid maker's directions say; current Ball and Kerr lids need only washing [5]. See lids and bands.
What does not count as sterilizing
| Method | Sterilizes jars? | What the sources say |
|---|---|---|
| Dishwasher cycle | No | Fine for washing and for keeping clean jars warm until filling [1], but dishwasher water is "far below that required to kill harmful microorganisms" (Penn State) [6] |
| Dishwasher "sanitize" setting | Not established | No source reviewed treats it as a substitute for NCHFP's boiling method. Use it to wash, then boil |
| Oven ("dry heat") | No, and it is risky | Canning jars are not designed for intense dry heat and may shatter; heat also moves into glass more slowly through air than through water [6][7] |
| Pouring boiling water into jars | No | The jars are not held under boiling water for 10 minutes [1] |
| Microwave | No | Penn State says microwaves heat unevenly and jars can explode [6] |
The oven method is common in British recipes, where jars are dried in a low oven, filled hot and capped without a water bath. That system and the reasons US guidance moved away from it are on paraffin, inverting jars and other old methods.
When to sterilize even though you could skip it
Skipping sterilization means a longer process: at every elevation, the unsterilized-jar time is the longer of the two [1][3]. Extra minutes in boiling water rarely matter for a firm-setting jam, but they can soften a delicate one. UGA prefers pre-sterilized jars for fruits that are not naturally high in pectin, because "the longer process time in the canner without pre-sterilized jars may weaken these gels" [4]. UC Master Food Preservers add that lengthening the process to avoid sterilizing is acceptable but "not always preferable" for this reason [2].
| Choose sterilized jars and the shorter time when | Skipping sterilizing is fine when |
|---|---|
| The fruit is low in natural pectin, as strawberry, cherry, peach, pear and blueberry usually are | The fruit is naturally high in pectin and sets firmly (check the fruit chart) |
| The recipe is a soft-set preserve or whole-fruit preserve | You are making a firm jelly or a long-cooked jam |
| You live at a high elevation, where the gap between the two times is 10 to 15 minutes | You are processing a Ball recipe, which uses a 10 minute base anyway |
| The batch was hard won and you want every advantage on the set | You are running many batches and want fewer steps |
Pectin content by fruit is covered on where the pectin is.
Sterilizing the jars does no harm in any recipe; it only costs time and energy [2]. It does not let you shorten a recipe's tested time below what that recipe's own chart says.
Clean, sterile and hot are three different things
Every canning jar needs to be clean: washed with detergent and rinsed [1]. Washing does not sterilize [8]. Every jar also needs to be hot when it is filled, so the hot jam does not crack it and the canner comes back to a boil quickly. Only jars for a process under 10 minutes need to be sterile as well. Getting these three straight is most of the job.
Your processing time, with or without sterile jars
Once you know which kind of jar you have, take that answer to the chart on how long to process jam, where both rows are laid out by elevation with a worked example.
References
- National Center for Home Food Preservation, Do I need to pre-sterilize my jars before canning?, May 21, 2014. https://nchfp.uga.edu/blog/do-i-need-to-pre-sterilize-my-jars-before-canning
- UC Master Food Preserver Program, Preserve It: Canning Basics, Sterilizing Canning Jars (Part 1 of 2), revised July 2025. https://ucanr.edu/sites/default/files/2021-11/PIP-Jars%20sterilizing%20jars1-WhenWhy-revJuly2025.pdf
- USDA and National Center for Home Food Preservation, Complete Guide to Home Canning, Guide 7: Preparing and Canning Jams and Jellies, revised July 2015. https://nchfp.uga.edu/papers/guide/GUIDE07_HomeCan_rev0715.pdf
- University of Georgia Extension, Andress, Preserving Food: Processing Jams and Jellies, FDNS-E-37-1, revised June 2011. https://openscholar.uga.edu/record/23661/files/FDNS-E-37-1.pdf
- Kansas State University Research and Extension, Blakeslee, What Causes Canning Lids to Buckle?, You Asked It!, June 25, 2026. https://www.k-state.edu/news/you-asked-it/articles/2026/06/what-causes-canning-lids-to-buckle.html
- Penn State Extension, Canners and Canning Methods that are Not Recommended, updated November 12, 2015 (copy hosted by UC ANR). https://oc4h.ucanr.edu/sites/default/files/2020-10/337831.pdf
- Oregon State University Extension, Hyde, Safe canning practices for jam?, June 2013, reviewed 2024. https://extension.oregonstate.edu/ask-extension/featured/safe-canning-practices-jam
- National Center for Home Food Preservation, Recommended Jars and Lids (from USDA Complete Guide to Home Canning, Agriculture Information Bulletin 539, revised 2015), viewed October 2026. https://nchfp.uga.edu/how/can/general-information/recommended-jars-and-lids/
