How long do you process jam, and how does altitude change it?

Most jam in half-pint or pint jars is processed for either 5 or 10 minutes at sea level, and the difference comes down to the jars. USDA recipes use 5 minutes with jars you sterilized first, rising to 10 minutes from 1,001 to 6,000 feet and 15 minutes above that [1]. If you skip sterilizing, or follow a Ball recipe, the starting time is 10 minutes, rising in 5 minute steps by altitude band [2][3]. Use the time and altitude chart from the same source as your recipe, and never put one system's altitude steps on the other's base time. This page gives both charts and shows you how to pick the right row.

The one rule: keep each recipe with its own chart

Two sets of processing times for jam are in wide use, and both are sound. They differ because they start from different jars.

• USDA's 5 minute time assumes sterile jars. Guide 7, USDA's jam and jelly chapter, tells you to fill "sterile jars" and to use "pre-sterilized Mason canning jars, self-sealing two-piece lids, and a 5-minute process" [1].
• The 10 minute time sterilizes the jars as it goes. The National Center for Home Food Preservation (NCHFP) explains that jars covered by boiling water for 10 minutes are sterilized during processing, so a process of 10 minutes or more needs no separate sterilizing step. It also notes that some people choose to raise a 5 minute jam process to 10 minutes for exactly this reason [2]. The 10 minute method most Ball recipes use starts from the same place [3].

The common mistake, repeated across many canning blogs, is to take one system's base time and the other system's altitude steps. Adding the 5, 10, 15 and 20 minute steps from a Ball chart to USDA's 5 minute base gives times too short for unsterilized jars at every elevation. Putting USDA's three wide bands on a 10 minute base gives a figure no source published. Keep the pair together.

Both charts, side by side

These times are for half-pint and pint jars in a boiling water canner, with the water at a full boil before timing starts.

Sources: the sterilized-jar row is Guide 7's table for jams and jellies, which gives 5 minutes at 0 to 1,000 feet, 10 minutes at 1,001 to 6,000 feet and 15 minutes above 6,000 feet [1]. The unsterilized-jar row takes NCHFP's full 10 minute process for unsterilized jars [2] and applies the altitude steps from South Dakota State University's chart: add 5 minutes at 1,001 to 3,000 feet, 10 at 3,001 to 6,000, 15 at 6,001 to 8,000 and 20 at 8,001 to 10,000 [3]. That chart cites the 2016 Ball canning book, so if you own a current Ball book, check its chart against this row. A Pomona's Pectin jam recipe reproduced by UC Master Food Preservers of Sacramento County gives the same pattern: 10 minutes, or 15 minutes at 1,001 to 3,000 feet [4]. Pomona's general directions, in another UC handout, add 1 minute per 1,000 feet to the 10 minutes instead [9]. For a Pomona jam this page uses the band row, which is never the shorter of the two.

Wherever the two rows differ, the unsterilized row is the longer one. That is why the choice matters most for soft-setting fruit (see below), and why the book's processing time calculator asks whether you sterilized your jars before it gives you a number.

Finding your row

Fruit butters, low-sugar spreads and marmalades often carry their own times. Use the time in the tested recipe for that product; apple butter and other fruit butters covers butter times by source.

Worked example: a Treasure Valley kitchen

Start with your own address: Penn State suggests simply searching "elevation" with it [7]. For a rough check, the floor of the Boise River valley sits between about 2,500 and 2,800 feet. The U.S. Geological Survey's Boise Folio, from field surveys in 1895 and 1896, put the river just below 2,500 feet at the western edge of its map and the valley alluvium near Table Rock at 2,800 feet [6]. Kitchens in Boise and Eagle are therefore in the 1,001 to 3,000 foot band.

Say you are making a USDA strawberry jam with powdered pectin in half-pints.

Option A: sterilize the jars.

1. Boil the empty jars for 12 minutes: 10 minutes, plus 1 minute for each 1,000 feet above 1,000, rounding any part of 1,000 feet up [2].
2. Fill and lid them, and process for 10 minutes (sterilized-jar row, 1,001 to 6,000 ft) [1].

Option B: skip sterilizing.

1. Wash the jars and keep them hot.
2. Fill and lid them, and process for 15 minutes (unsterilized-jar row, 1,001 to 3,000 ft) [2][3].

The same jam in a Ball recipe takes 15 minutes in Boise whether or not you sterilize.

Why this page says 15 minutes and not 12

You will see 12 minutes quoted for unsterilized jars at Boise elevations. It comes from a University of Georgia bulletin, which gives a 10 minute process for unsterilized jars followed by an instruction to add 1 minute per 1,000 feet [5]. At 2,700 feet that works out to about 12 minutes.

This book uses 15 minutes instead, for four reasons:

1. The UGA sentence speaks of adding 1 minute of "sterilizing time" per 1,000 feet [5]. NCHFP's general pages also carry a 1 minute per 1,000 feet rule, and it too is for boiling empty jars to sterilize them [2], a different job from processing filled jars. Read as a processing adjustment, either one gives the 12 minute figure.
2. Every published altitude adjustment for a jam process steps by band. Guide 7 steps 5 minutes at 1,000 feet [1]; the SDSU chart steps 5 minutes per band [3]; the Pomona recipe gives 15 minutes at 1,001 to 3,000 feet [4]. Fifteen minutes agrees with all three.
3. The band figure is never shorter than the per-minute figure at any elevation (15 against 12 at 2,700 feet; 20 against about 15 at 5,000 feet). Choosing it never puts you below what any source asks.
4. Whole bands are easier to read correctly at the stove.

No source has published a direct ruling on unsterilized jars at this elevation, and Pomona's general directions take the per-minute reading [9]. The 15 minutes is this book's reading of the published band charts, chosen because it is never shorter than any of them.

If you want the shortest possible time, for a soft-setting fruit for instance, the way to get it is to sterilize the jars and use the sterilized-jar row: 10 minutes in Boise.

When a shorter time is worth the sterilizing

Extra minutes in boiling water do not harm most gels, but they can soften the set of a fruit low in natural pectin. UGA's bulletin says pre-sterilized jars are preferred for fruits not naturally high in pectin because the longer process "may weaken these gels" [5], and UC Master Food Preservers make the same point about 5 minute jams [8]. Strawberry, cherry, peach, pear and blueberry are the usual candidates. For those, the sterilized-jar method is the better choice, especially at elevation, where the gap between the rows grows.

Jar sizes and canner type

Guide 7's jam and jelly times are written for half-pints and pints, and the times are the same for both [1]. It gives no time for quarts; do not can jam in quart jars unless a tested recipe gives a quart time. For 4 ounce and 12 ounce jars, see which jars you can can jam in.

An atmospheric steam canner uses the same time as the boiling water recipe, including the altitude adjustment, with a ceiling of 45 minutes in total [7]. Every jam time on this page fits under that ceiling. The rules for running one are on steam canning jam.

Altitude changes one more number in jam making: the temperature at which no-pectin jam sets. The two effects are shown together on how altitude changes jam making.

Getting the sterilizing step right

If your answer above is the sterilized-jar row, the timing of the sterilizing boil, what counts as sterile and what does not (dishwashers and ovens do not) are on do you need to sterilize jars.

References

1. 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
2. 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
3. South Dakota State University Extension, Kleine and Botzet, A Guide to Water Bath Canning (P-00255), 2022 (altitude chart citing The All New Ball Book of Canning and Preserving, 2016). https://extension.sdstate.edu/sites/default/files/2022-10/P-00255-v2.pdf
4. UC Master Food Preservers of Sacramento County, Apples, Pears and Persimmons (demonstration handout, including Pomona's Pectin low-sugar persimmon jam), October 16, 2024. https://ucanr.edu/sites/sacmfp/files/403327.pdf
5. 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
6. U.S. Geological Survey, Geologic Atlas of the United States, Boise Folio (Folio 45), Description of the Boise Quadrangle, from 1895 and 1896 field surveys. https://pubs.usgs.gov/gf/045/text.pdf
7. Penn State Extension, Zepp, How to Use an Atmospheric Steam Canner, updated March 17, 2025. https://extension.psu.edu/how-to-use-an-atmospheric-steam-canner
8. 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
9. University of California Master Food Preserver Program, Pomona's Cooked Fruit Spreads (handout, posted March 2025). https://class.ucanr.edu/sites/default/files/2025-03/MFP%20Pomona%20Cook%20Fruit%20Spreads.pdf