Can homemade jam give you botulism?

Jam made from ordinary acidic fruit, by a tested recipe, is one of the lowest-risk foods you can can at home. Botulism bacteria cannot grow in food with a pH of 4.6 or below, most fruits sit well under that line, and the sugar in jam ties up much of the water those bacteria would need. That is why federal rules exclude jams, jellies and preserves from the acidified food regulation. The risk enters when the jar holds something that is not acidic fruit: peppers, onion, garlic, pumpkin, a low-acid fruit without its added acid, or a recipe nobody tested. This page shows where that line runs and how mold differs from botulism.

Why fruit jam sits on the safe side

Botulism comes from a toxin made by Clostridium botulinum, a soil bacterium whose spores survive boiling. The spores do no harm unless they can grow, and growing needs a combination jam does not offer: low acid, moisture, and no air.

Two numbers in federal food law mark the boundary:

• pH 4.6. Federal rules define low-acid foods as those with a finished equilibrium pH above 4.6 and a water activity above 0.85 [1]. Acid foods have a natural pH of 4.6 or below [1]. Extension programs that test home-made products for sale use the same line; Oregon State's pH training says products sold under Oregon's farm direct law must be 4.6 or below, and ties values above 4.6 to botulism risk [2].
• Water activity 0.85. Water activity measures how much of a food's water is free for microbes to use [1]. Sugar binds water; Penn State notes that the high sugar in jam reduces the water available to support microbial activity [3].

Jam is usually well inside both lines. The pH range at which jams and jellies gel best is 2.8 to 3.3, far below 4.6, and a standard jam or jelly is cooked to at least 65 percent soluble solids [3]. Federal acidified food rules list "jams, jellies, preserves" among the products excluded from their coverage [1].

A boiling water canner does not destroy the bacteria that matter in a low-acid food; Penn State makes that point about white peaches, which have no safe water bath or steam canning process [5]. For jam the canner is enough because the acid keeps any spores from growing, while the process destroys the molds and yeasts that could spoil the jar and drives out air so the lid seals.

Where the risk gets in

Low-sugar jam and botulism

Cutting sugar changes the water side of the picture and leaves the acid side alone. A low-sugar jam made from acidic fruit is still an acid food, so botulism is not the main concern; spoilage is. With less sugar, molds and yeasts have more water to work with, which is why reduced-sugar products need their own tested methods and, in some cases, the refrigerator or freezer. The UC Master Food Preservers put it plainly for jams and jellies: too little sugar can lead to mold [9]. Tested routes are on how to make low-sugar jam that sets and keeps.

Mold and yeast are a different problem

Most jam that goes bad goes bad visibly. Mold grows on the surface; yeasts ferment the jam and leave bubbles, a sour or alcoholic smell and sometimes a domed lid. Neither is botulism, and both are reasons to throw the jar out.

Do not scrape mold off jam. USDA's advice for a moldy jar of jam or jelly is to discard the contents of the whole jar [10]. Some molds that grow on fruit products make mycotoxins, and patulin, a mycotoxin found in some home-made apple products, has been shown to cause cancer in animals, although its role in human disease is not clear [10]. The UC Master Food Preservers add that mycotoxins have no visible sign, taste or smell [9].

Mold can open the door to botulism. In acid foods, mold growth can raise the pH, which can allow botulism-causing bacteria to grow where they otherwise could not [9]. That is the main reason a moldy jar of anything is never "probably fine underneath."

The usual causes are seals that failed or were never real: paraffin, which shrinks and cracks and is no longer considered an acceptable seal for any sweet spread [10]; inverting jars instead of processing them; jars that were underprocessed; and low-sugar jam from a full-sugar recipe. Paraffin, inverting jars and other old methods explains why those methods were dropped.

What a spoiled jar looks like

Botulism toxin can be present in food that looks and smells normal, which is why the defense is the recipe and the process rather than inspection. Still, discard any jar of jam that shows:

• a bulging, loose or unsealed lid that was sealed before
• liquid leaking from under the lid
• liquid or foam that spurts when you open it
• an off, yeasty or alcoholic smell
• bubbles that move or rise after the jam has set
• mold of any color, on the surface or under the lid

How to tell a jar has gone bad covers each sign and how to dispose of spoiled jars without spreading what is in them. Do not taste a jar you suspect.

If someone may be sick

Botulism is a medical emergency. The Illinois Poison Center lists its symptoms as including trouble breathing, swallowing or speaking, dry mouth, muscle weakness, blurred or double vision, drooping eyelids, nausea, vomiting, abdominal cramps and paralysis, usually beginning 12 to 36 hours after the food was eaten [11]. If anyone has those symptoms after eating a home-canned food you are unsure about, especially a low-acid or untested one, get emergency medical care right away (call 911 if breathing is affected) and tell the clinicians what was eaten and when. For advice on a possible exposure, Poison Help is 1-800-222-1222 [11]. Keep the jar and any leftovers, sealed in a bag and out of reach, so the health department can test them, and call your local health department.

Staying on the safe side, in four rules

1. Use a tested recipe for anything you put on the shelf. Recipes you can trust shows how to recognize one.
2. Do not reduce the acid (lemon juice, citric acid, vinegar) a recipe calls for, and use bottled lemon juice where the recipe says to.
3. Do not add low-acid ingredients to a recipe that did not include them.
4. Refrigerate or freeze anything untested, and throw out anything with mold.

The details of rule 3 are where most of the real-world questions sit. What you can change in a tested recipe goes through the common changes one by one.

References

1. Code of Federal Regulations, 21 CFR 114.3, Definitions (Cornell LII), current. https://www.law.cornell.edu/cfr/text/21/114.3
2. Oregon State University Extension Service, Clackamas County, pH meter calibrating and testing for pickled food products, December 19, 2022. https://extension.oregonstate.edu/node/198996
3. Penn State Extension, LaBorde, Food for Profit: Commercial Production of Jams, Jellies and Fruit Butters, updated May 24, 2024. https://extension.psu.edu/food-for-profit-commercial-production-of-jams-jellies-and-fruit-butters
4. National Center for Home Food Preservation, Beware: Pumpkin Butter, December 7, 2012. https://nchfp.uga.edu/blog/beware-pumpkin-butter
5. Penn State Extension, Morrow, Preserving White Peaches, updated March 22, 2024. https://extension.psu.edu/preserving-white-peaches
6. National Center for Home Food Preservation, Preserving the Fickle Fig, October 8, 2013. https://nchfp.uga.edu/blog/preserving-the-fickle-fig
7. Penn State Extension, Hassani, Why some old canning recipes are no longer safe, updated September 13, 2024. https://extension.psu.edu/why-some-old-canning-recipes-are-no-longer-safe
8. Penn State Extension, Zepp, Modified Food Starches, updated December 6, 2023. https://extension.psu.edu/modified-food-starches
9. UC Master Food Preserver Program, Benavides, Mold: Cut Off or Toss?, April 2025. https://ucanr.edu/node/152959
10. University of Georgia Extension, Andress, Preserving Food: Processing Jams and Jellies (FDNS-E-37-1), rev. June 2011. https://openscholar.uga.edu/record/23661/files/FDNS-E-37-1.pdf
11. Illinois Poison Center, Botulinum (undated page, accessed October 2026). https://illinoispoisoncenter.org/health-safety/food-poisoning/botulinum