My ferment stopped bubbling or smells off. What went wrong?

A ferment that goes quiet after a week or so is usually fine: the gassy first stage of fermentation naturally ends around then, and a pH reading will tell you whether acid is still building. A ferment that never started is usually too cold, too salty or made with the wrong salt. Slime, a putrid or rotten smell, or a pH that never drops below 4.6 or starts climbing back up means the batch has failed and should be thrown out [1] [2] [3]. Find what you are seeing below, read what it means, and follow what to do.

Before anything else: take a pH reading

Most of the problems on this page look alarming and turn out to be harmless, and a few look harmless and are not. A pH reading separates them faster than anything else. Snyder and coauthors expect a well-managed vegetable ferment to fall below pH 4.6 within about a week, and say brines that do not reach 4.6, or whose pH rises, should be discarded [2]. If you do not have a meter, see measuring pH. The rest of this page assumes you can check.

No bubbles at all after three days

What you see. The brine is clear, the mash has not risen, nothing happens when you tap the jar.

What it means. The bacteria have not taken hold yet, or gas is escaping where you cannot see it. The usual causes:

• The room is too cold. USDA's canning guide says sauerkraut may not ferment below 60°F [4].
• Iodized salt. Illinois Extension says it may slow fermentation [3].
• Much more salt than you intended. At 6 percent and above, the gassy early bacteria barely get going and a different, quieter species takes over from the start [5]. You will see far fewer bubbles even when acid is forming.
• A loose lid or airlock that lets gas out slowly, so bubbles never build up.
• Old, cooked or heavily washed produce with few bacteria on it.

What to do. Measure the pH. If it is falling, the ferment is working and you can leave it alone. If it has not moved, check your salt math against how much salt a pepper ferment needs and move the jar to 65 to 72°F, the optimal range given by Snyder and coauthors [2]. A spoonful of brine from a previous good ferment can help it start. If the pH is still not falling by the end of the first week, discard it.

It bubbled hard, then stopped around day 7 to 10

What you see. A lively first week, then almost nothing. "Hot pepper fermentation seems to have stopped 10 days into fermentation" is the title of one of many threads asking this on The Hot Pepper forum [6].

What it means. Usually nothing is wrong. The bacteria that start a vegetable ferment make carbon dioxide; USDA-ARS researchers report they die off after about a week and are replaced by acid-tolerant species that make lactic acid with little gas [5]. The ferment has moved into its quieter second stage.

What to do. Check the pH. If it is below 4.6 and still drifting down, or holding steady, the ferment is on track. Leave it for flavor, or finish it. How to read the trend is on knowing when a ferment is done.

The pH is stuck above 4.6, or it went down and is creeping back up

What you see. Readings that never cross 4.6, or a ferment that reached, say, 3.8 and now reads 4.2 and rising.

What it means. Either the ferment never acidified properly, or something is consuming the acid. A rising pH is the classic sign of film yeast or mold on the surface. In a USDA study, oxidative yeasts with access to air used up more than half the lactic acid in a fermented cucumber medium within three to four days and pushed the pH past 4.6 in six days [7]. Once the pH climbs above about 4.5, spoilage bacteria that make foul-smelling acids can take over [7] [5].

What to do. Discard it. Snyder and coauthors are explicit that ferments "that fail to reach a pH of < 4.6" or in which "a continued pH decline is not recorded" should be discarded [2]. A rising pH is the clearest case of a decline that has not continued. Next time, fix the air problem; see kahm yeast or mold.

The brine or the peppers feel slimy

What you see. Brine that is thick, stringy or ropy, or pepper pieces with a slick coating.

What it means. Unwanted microbes have grown. USDA's troubleshooting table for fermented pickles lists brine that is too weak, temperatures that are too high and too little brine as causes of soft or slippery pickles [8].

What to do. Discard it. Illinois Extension says fermented foods that appear slimy should be thrown out [3], and USDA's canning guide says the same for pickles that become soft, slimy or develop a disagreeable odor [4].

The peppers have gone soft or mushy

What you see. Pepper pieces that collapse when pressed, with no slime and a clean sour smell.

What it means. Several things soften peppers in a ferment:

• Heat. USDA's guide says sauerkraut may soften above 75°F and pickles become too soft above 80°F [4].
• Too little salt or too little brine [8].
• Oxygen. In a USDA study of acidified red bell peppers held at 86°F, peppers packed in air were about half as firm after two weeks as peppers packed without oxygen, and peppers lost at least 40 percent of their firmness in two weeks overall [9].
• Enzymes from mold. In commercial cucumber ferments, softening has been traced to mold enzymes brought in on blossoms still attached to the fruit [5].

What to do. For a sauce, softness by itself is a texture issue, since you are going to blend it anyway. If the smell is clean and sour, there is no slime, and the pH is well below 4.6, you can use it. If softness comes with slime, a bad smell or a high pH, discard it. For whole fermented peppers you want to keep firm, ferment cooler, salt at the top of the 2 to 3 percent range and keep the jar well sealed.

A sulfur or eggy smell

What you see. A sharp, eggy or cabbage-like smell, often in the first week, especially with garlic, onion or cabbage in the mix.

What it means. Makers commonly report sulfur notes in ferments that include garlic and onion, which are rich in sulfur compounds. No extension or USDA source checked sets out when a sulfur smell is normal and when it is not, so judge it by what else you see. UC Davis gives the clearest line: a fermented vegetable "will smell pleasantly sour but not putrid" [1].

What to do. If the sulfur smell sits on top of a clean sour smell, the pH is falling and there is no slime or mold, give it time; it often fades as the ferment matures. If it smells rotten rather than sulfurous, go to the next section.

A rotten, putrid, cheesy or vomit-like smell

What you see. A smell that makes you pull back from the jar.

What it means. The ferment has failed. UC Davis says a putrid smell indicates a failed fermentation [1]. USDA-ARS researchers describe how spoilage after the pH rises produces propionic and butyric acids, which smell foul [5].

What to do. Discard it. Illinois Extension: if fermented foods smell spoiled or rotten, discard them [3]. Do not taste it to check.

A yeasty, bready or boozy smell

What you see. A winey or beer-like aroma, sometimes with lots of fine bubbles, common in ferments with fruit, carrots or added sugar.

What it means. Fermentative yeasts are active alongside the bacteria, turning sugar into alcohol and carbon dioxide [5]. That is part of how many pepper ferments taste, and it is not a safety sign by itself. It does tell you there is still sugar and live yeast, which matters when you bottle.

What to do. Check the pH and let it finish. Before bottling, plan how to stop the yeast, because a yeasty sauce that goes into a sealed bottle unheated is the usual cause of bottles that burst or ooze.

The brine overflowed or the level dropped

What you see. Liquid on the counter in the first days, then peppers poking above the brine.

What it means. Gas lifted the mash and pushed brine out. Normal in the first week.

What to do. Press the solids back down and top up with brine at the same salt percentage as the ferment, so you do not dilute it. Set the jar on a plate. Peppers that sat exposed for days are where mold starts, so look closely at the surface.

Cloudy brine and white sediment

What you see. Milky brine and a fine white layer settling on the bottom or on the peppers.

What it means. Normal. USDA's troubleshooting table names bacteria from fermentation, and salt with anti-caking agents, as causes of white sediment [8].

What to do. Nothing. Use additive-free salt next time if you want clearer brine.

Browning or dull color

What you see. Peppers or mash darkening, especially in the top layer.

What it means. Exposure to air at the surface, iodized salt, or reactive metal. Illinois Extension says iodized salt can brown vegetables [3], and USDA lists iron, copper, brass and zinc utensils among the causes of dark pickles, adding that pickles made with brass, copper or zinc utensils should not be used [8].

What to do. Darkening from air or iodized salt is a quality issue. If reactive metal touched the ferment, discard it. Keeping red and orange sauces bright after fermenting is covered on keeping the color in your sauce.

Fixing the next batch

Most failures come back to four settings: salt between 2 and 3 percent of total weight, every piece under liquid, a room between 65 and 72°F, and clean produce and equipment. If your batch failed on the surface, the fix is usually air; see kahm yeast or mold for prevention.

References

1. DiCaprio E, Marco M, Finnegan P, Hanlon M, Common issues with fermented fruits and vegetables, UC Davis and UC ANR, version 1.0, March 15, 2022. https://ucfoodsafety.ucdavis.edu/sites/g/files/dgvnsk7366/files/media/documents/Troubleshooting%20fermented%20fruits%20and%20vegetables%20FINAL.pdf
2. Snyder A, Breidt F, Andress EL, Ingham BH, Manufacture of Traditionally Fermented Vegetable Products: Best Practice for Small Businesses and Retail Food Establishments, Food Protection Trends 40(4):251-263, 2020. https://www.ars.usda.gov/ARSUserFiles/60702500/Fermented%20Veg%20Manuscripts/p437.pdf
3. University of Illinois Extension, Fermenting FAQ, undated, accessed October 2026. https://extension.illinois.edu/food-preservation/fermenting-faq
4. USDA and National Center for Home Food Preservation, Complete Guide to Home Canning, Guide 6: Preparing and Canning Fermented Foods and Pickled Vegetables, revised 2015. https://nchfp.uga.edu/papers/guide/GUIDE06_HomeCan_rev0715.pdf
5. Breidt F, Pérez-Díaz IM, McFeeters RF, Lee CH, Fermented Vegetables, chapter 33 in Doyle and Buchanan, eds., Food Microbiology: Fundamentals and Frontiers, 4th ed., ASM Press, 2013. https://www.ars.usda.gov/ARSUserFiles/60701000/Pickle%20Pubs/p380.pdf
6. The Hot Pepper forum, hot pepper fermentation seems to have stopped 10 days into fermentation (thread). https://thehotpepper.com/threads/hot-pepper-fermentation-seems-to-have-stopped-10-days-into-fermentation.75164/post-1723767
7. Franco W, Pérez-Díaz IM, Role of selected oxidative yeasts and bacteria in cucumber secondary fermentation associated with spoilage, Food Microbiology 32:338-344, 2012. https://www.ars.usda.gov/ARSUserFiles/60701000/Pickle%20Pubs/p378.pdf
8. National Center for Home Food Preservation, Causes and Possible Solutions for Problems with Fermented Pickles, adapted from So Easy to Preserve, 6th ed., 2014 (reviewed 2020). https://nchfp.uga.edu/how/ferment/general-information-on-fermenting/causes-and-possible-solutions-for-problems-with-fermented-pickles/
9. McFeeters RF, Barrangou LM, Barish AO, Morrison SS, Rapid Softening of Acidified Peppers: Effect of Oxygen and Sulfite, Journal of Agricultural and Food Chemistry 52(14):4554-4557, 2004. https://www.ars.usda.gov/ARSUserFiles/60701000/Pickle%20Pubs/p327.pdf