My sauce looks or smells different. Is it still safe?

Some changes are harmless and some mean the bottle goes in the trash. Throw it out if the cap or lid is bulging or leaking, if the sauce spurts or foams when opened (unless it is a raw ferment you know is still alive), if you see fuzzy mold of any color, or if it smells rotten. The CDC lists all of these as signs of contamination [1]. Darkening, fading and a layer of liquid on top are usually quality changes you can shake or live with. Remember that the most dangerous problem, botulinum toxin, cannot be seen, smelled or tasted [1]. Below, each sign is explained by what you see, what it means and what to do.

The quick check

The reason the middle column differs is simple: a raw fermented sauce is supposed to have live microbes making gas. A cooked, canned or commercial shelf-stable sauce is not, so the same sign means something went wrong.

Signs that mean throw it out

A bulging cap, a swollen lid or a leak

What you see. The cap domes upward, a canning lid has popped up and flexes, a plastic bottle feels tight and hard, or sauce has crept out under the cap.

What it means. Something inside is making gas. In a cooked, canned or store-bought sauce, that means microbes are growing in a product that should have none. Researchers studying spoiled commercial hot sauces have isolated a yeast, Pichia manshurica, and a lactic acid bacterium, Lactobacillus curvatus, from them [2]; organisms like these survive a weak process or get in through a poor seal. The CDC lists a container that is "leaking, bulging, or swollen" as a sign of contamination [1].

What to do. Do not taste it. Open it, if you must, over a sink and pointed away from your face, because a pressurized bottle can spray. Throw it out. If several bottles from one batch swell, the batch had a process or seal problem; for a fermented sauce, see why fermented sauce bottles burst.

Spurting or foaming when opened

What you see. Sauce shoots out or foams up when the cap comes off.

What it means. Gas under pressure, the same cause as a bulging cap. The CDC lists a container that "spurts liquid or foam when opened" as a sign of contamination [1].

What to do. Throw out any cooked, canned or store-bought sauce that does this. A raw ferment is the exception, covered below.

Fuzzy mold, any color

What you see. Raised, fuzzy or cottony spots, white, green, blue, gray, black or pink, on the surface, the rim or the inside of the cap.

What it means. Mold grows well in acidic foods; the USDA notes molds thrive in high-acid foods such as pickles and tomatoes, and tolerate salt and sugar better than most microbes [3]. Their root threads reach below the surface in soft and liquid foods, and some molds make toxins that spread through the food [3]. In a ferment, UC Davis food scientists treat fuzzy green, blue, brown or black mold as a sign the fermentation has failed [4].

What to do. Throw out the whole bottle. Do not scoop the mold off and use the rest; USDA microbiologists advise against doing that even for jams and jellies [3]. Do not sniff it; USDA warns that sniffing moldy food can cause breathing problems [3]. Wipe the shelf where it sat; USDA suggests cleaning the refrigerator interior with 1 tablespoon of baking soda dissolved in a quart of water, then rinsing and drying [3].

A rotten or putrid smell

What you see. A smell of rot, garbage or sewage, very different from the sauce's usual sharp, sour or fruity smell.

What it means. Spoilage organisms have taken over. In a ferment, UC Davis food scientists say a putrid smell indicates a failed fermentation [4]. The CDC lists food that "smells bad" as a sign of contamination [1].

What to do. Throw it out. Do not taste it to confirm.

A yeasty or alcoholic smell in a cooked sauce

What you see. The sauce smells like bread dough, beer or wine, and may taste fizzy.

What it means. Yeasts are fermenting the sugars. A cooked or bottled sauce should not be fermenting, so they got in after cooking, survived a cool fill, or found a bad seal.

What to do. Throw it out. If it happens more than once, look at your fill temperature, your bottles and caps, and any fruit or sugar in the recipe.

You do not know how it was made or how long it sat out

What you see. A gift bottle with no label, a sauce that spent a weekend in a hot car, or a jar from the back of the fridge with no date.

What it means. You cannot judge safety from the outside. The CDC's guidance is not to eat food if you do not know whether it was safely canned, preserved or fermented: "If in doubt, throw it out!" [5]

What to do. Throw it out, and start dating your bottles. Keeping times by sauce type are on how long homemade hot sauce lasts.

Signs that depend on the kind of sauce

Fizz, gas and a swollen cap in a raw ferment

What you see. A raw fermented sauce, never cooked, hisses when opened, shows small bubbles, or pushes its cap up.

What it means. The ferment is still alive. Bacteria and yeasts keep producing carbon dioxide. UC Davis food scientists describe gas and swelling in fermented vegetables as no problem as long as the pH stays below 4.6, to be handled by venting the container or using an airlock [4].

What to do. Vent the bottle over the sink, refrigerate it to slow the fermentation, and check the other signs: if there is also mold, a rotten smell or slime, throw it out. If you have a pH meter, a reading well under 4.6 is reassuring. To stop it happening, see finishing a ferment for the bottle.

A white film on the surface

What you see. A flat, white or cream-colored film, sometimes wrinkled, on the surface of the liquid.

What it means. In an open ferment, a flat white film is usually kahm yeast, which grows at the air surface. UC Davis says it is not a reason to discard a ferment by default, but the pH should be checked to make sure it stays at or below 4.6 [4]. In a finished bottle of cooked or store-bought sauce, any surface growth means microbes got in after processing.

What to do. In a ferment, skim it and check the pH; telling kahm from mold is covered on kahm yeast or mold. In a finished, bottled sauce, throw it out.

Signs that are usually quality changes

Darker, browner or faded color

What you see. A red sauce turns brick or brown, an orange sauce goes dull, a green sauce turns olive.

What it means. Pigments break down over time with heat, light and air. Mike Hultquist of Chili Pepper Madness reports gradual discoloration even in his well-acidified sauces [6], and light exposure fades color in jarred foods [7]. By itself, color change is a quality issue.

What to do. Use it if nothing else is wrong. To slow it next time, store in the dark and the cold, and keep less air in the bottle. The chemistry behind each color change is on keeping the color in your sauce.

Liquid separating on top

What you see. A layer of thin, clear or colored liquid above the pepper solids.

What it means. The solids are settling out of the liquid. That affects texture and looks, and does not make the sauce unsafe.

What to do. Shake it. If it bothers you, blending longer or adding a stabilizer will hold it together; see stopping separation.

Sediment or a cloudy bottom

What you see. Fine particles settled at the bottom, or a cloudy layer.

What it means. Usually pepper solids or spices settling. In pickled foods, the National Center for Home Food Preservation traces white sediment to salt containing anti-caking agents [7].

What to do. Shake and use it, unless it comes with fizzing, a bulging cap or a bad smell, in which case treat it by those signs.

If someone feels sick after eating sauce

Botulism is rare but serious, and its signs include difficulty swallowing, double or blurry vision, drooping eyelids, slurred speech, muscle weakness and difficulty breathing, sometimes with nausea, vomiting or stomach pain first [8]. The CDC calls botulism a medical emergency: see a doctor or go to the emergency room immediately [8]. Keep the bottle for health officials. Why a sauce can carry this risk, and how acid prevents it, is on botulism and hot sauce.

Keeping the next batch from going wrong

Spoilage often starts with a keeping time ignored, a dirty spoon, or a fermented sauce bottled while still active. Keeping times for every type of sauce, and the habits that stretch them, are on how long homemade hot sauce lasts.

References

1. Centers for Disease Control and Prevention, Home-Canned Foods, April 25, 2024. https://www.cdc.gov/botulism/prevention/home-canned-foods.html
2. Lobo Chinchilla, A., C. Zúñiga Arrieta, R. W. Worobo, O. I. Padilla Zakour and J. Usaga Barrientos, Fate of Spoilage and Pathogenic Microorganisms in Acidified Cold-Filled Hot Pepper Sauces, Journal of Food Protection 82(10):1736-1743, 2019 (record at University of Costa Rica repository). https://www.kerwa.ucr.ac.cr/items/d13ae886-62d0-4f48-81b7-b7b8377dd160/full
3. USDA Food Safety and Inspection Service, Molds on Food: Are They Dangerous?, revised August 2013. https://www.fsis.usda.gov/sites/default/files/media_file/2021-02/Molds_on_Food.pdf
4. University of California, Davis, Erin DiCaprio, Maria Marco, Peter Finnegan and Melanie Hanlon, Common Issues with Fermented Fruits and Vegetables, version 1.0, March 15, 2022. https://ucfoodsafety.ucdavis.edu/sites/g/files/dgvnsk7366/files/media/documents/Troubleshooting%20fermented%20fruits%20and%20vegetables%20FINAL.pdf
5. Centers for Disease Control and Prevention, Botulism Prevention, February 26, 2026. https://www.cdc.gov/botulism/prevention.html
6. Chili Pepper Madness, Mike Hultquist, Refrigerating Hot Sauce, January 3, 2023, modified February 17, 2025. https://www.chilipeppermadness.com/frequently-asked-questions/refrigerating-hot-sauce
7. National Center for Home Food Preservation, Causes and Possible Solutions for Problems with Pickled Foods, adapted from So Easy to Preserve, 6th edition, 2014. https://nchfp.uga.edu/how/pickle/general-information-pickling/causes-and-possible-solutions-for-problems-with-pickled-foods/
8. Centers for Disease Control and Prevention, Symptoms of Botulism, April 1, 2024. https://www.cdc.gov/botulism/signs-symptoms/index.html