Exploring the Dangers of Lacto-Fermentation

In the world of food preservation, lacto fermentation stands as a time-honored technique, known for its ability to transform ordinary ingredients into flavorful delicacies, creating probiotic richness and tangy delights. There’s no reason to fear fermentation.

Done right, fermented vegetables are safer than their raw counterparts. But let’s discuss the hidden lacto-fermentation dangers; to understand signs of a bad ferment and potential food borne pathogens.

Be empowered to ferment with confidence.

What is the lacto-fermentation method?

First, what is lacto-fermentation, also known as lactic acid fermentation. It’s a process where sugars in food are converted into lactic acid, acetic acid (as with vinegar) and C02.

The conversion creates “antimicrobials” and reduces the pH of the food resulting in a shelf stable, tangy flavored, delicately textured food. 

Is lacto-fermentation a risk factor for botulism?

When you follow good food handling practices and proper fermentation techniques, fermented foods can be safer than raw foods. Although botulism grows in anaerobic environments (like fermenting), the risk is mitigated when food is uncontaminated, and handled with clean hands and equipment.

If you’re new to fermenting, or just want additional reassurance, use pH tests strips and test that your ferments fall below a pH of 4.6.

Food borne pathogens in fermentation 

Lacto fermentation, while a natural and safe process when executed correctly, can pose dangers if not approached with care. From the threat of harmful pathogens to the nuances of fermentation conditions, navigating these risks is essential to ensure the safety of fermented foods.

Here is a list of the most common foodborne pathogens in fermentation

Clostridium botulinum (discussed above):

Escherichia coli (E. coli)

  • Certain strains of E. coli can cause foodborne illness, leading to symptoms such as diarrhea, abdominal pain, and fever. 
  • While not typically associated with fermentation, contamination with fecal matter or other sources of E. coli during handling or processing could pose a risk, which is why we clean our area.


  • Salmonella bacteria can contaminate fermented foods if raw ingredients are not properly handled or if equipment and surfaces are not adequately sanitized. 
  • Consumption of foods contaminated with Salmonella can lead to salmonellosis, causing symptoms like diarrhea, fever, and abdominal cramps.
  • Ensuring your ferment reaches a pH of less than 6.5 will mitigate this risk, most ferments reach a tangy flavor with a pH of <4.0.

Listeria monocytogenes

  • Listeria can survive and even grow at refrigeration temperatures, making it a concern in fermented foods that are not properly handled or stored, but if your pH is less than 6, your ferments should be safe. 
  • Listeriosis, the illness caused by Listeria monocytogenes, can be severe, particularly in pregnant women, newborns, the elderly, and individuals with weakened immune systems.

Staphylococcus aureus

  • Staphylococcus aureus can produce toxins that cause food poisoning if fermented foods are contaminated with the bacteria and then stored at improper temperatures. Proper hand washing is important.
  • Symptoms of staphylococcal food poisoning include nausea, vomiting, abdominal cramps, and diarrhea.

Clostridium perfringens

  • This bacterium can produce toxins that cause food poisoning, typically associated with improperly processed or stored foods. 
  • While less common in fermented foods, contamination could occur if proper sanitation practices are not followed. A pH of less than 5 will reduce risk.

Gosh, I remember when I was a Michigan State, our food safety professor would make the most ridiculous dad jokes about food safety. I loved them, because that’s my type of humor. Things like “When pressed, what did the grapes say was their favorite musical instrument?” They replied “cabernet”. Get it, cabaret??

Food safety is no joke.

When practicing proper fermentation steps and ensuring your ferments are at a pH of less than 4.6, the dangers are low. In fact, ferments done right are safer than raw foods. 

rotten apples pose a danger to lacto fermentation

Signs your ferments are not safe

Ensuring the safety of fermented foods is crucial to prevent foodborne illness. Here are some signs that your ferments may not be safe to consume:

  • Foul Odor: If your ferment emits foul or putrid odors, it may be a sign of spoilage due to the growth of harmful bacteria or molds.
  • Unusual Colors: While some changes in color are normal during fermentation, especially in vegetables, certain discolorations may indicate spoilage. For example, pink or black discoloration in sauerkraut or pickles can signal the presence of harmful bacteria or molds.
  • Mold Growth: While certain molds like kahm yeast are harmless and can be skimmed off the surface of the ferment, the presence of fuzzy or slimy mold growth is a sign of spoilage. If mold appears on the surface or throughout the ferment, it’s best to discard the entire batch.
  • Slimy Texture: Fermented foods should have a firm texture or slight crunch, depending on the type of food being fermented. If the texture becomes slimy or mushy, it may indicate the growth of undesirable bacteria or yeast.
  • Unpleasant Taste: Lactic acid fermentation imparts a tangy or sour flavor to foods, which is considered desirable. However, if your ferment tastes exceptionally bitter, putrid, or unpleasant, it may indicate spoilage or the presence of toxins produced by harmful microorganisms.
  • Excessive Gas or Pressure Build-Up: While some bubbling or gas production is normal during fermentation, excessive pressure build-up in fermentation vessels can be dangerous. If jars or containers become swollen, bulging, or exhibit signs of leakage, it may indicate the production of harmful gasses like hydrogen sulfide or carbon dioxide.

If you observe any of these signs, it’s best to err on the side of caution and discard the ferment to avoid the risk of foodborne illness. 

If you’d rather buy your ferments, learn how with my blog on how to find a truly fermented food.

Clean vs Sterile 

Now that we know the dangers, let’s talk about the intricacies of lacto fermentation at home. Beginning with your set up. 

First, we clean. Cleaning requires washing hands, jars and counters. This is important whenever working with food to avoid transferring things like e coli. 

On the other hand, there is sterility. Which a surgeon needs for surgery. This requires alcohol or excessive heat. In my opinion, your space does not need to be sterile, in fact, by doing so you void your space of all living organisms. After all, aren’t these the organisms we want to transform our food? 

  1. So, clean your area with soap and water. 
  2. Ensure jars, lids and utensils are clean and free of rust, cracks, etc.
  3. And always use fresh, healthy produce. Fermentation does not bring food back to life. 

Choosing safe and healthy produce

As mentioned in number three above, let’s start with quality produce. As with any preservation technique, you cannot bring a bruised, blemished, moldy or otherwise food back to life.

  • Choose fresh, ripe, raw produce which will provide better flavor, color and texture compared to produce that is overripe, bruised, or otherwise of poor quality. 
  • Preserve as soon as possible after harvesting. High-quality produce typically contains more nutrients, enzymes, and beneficial microorganisms that contribute to the fermentation process. As produce ages these things diminish.
  • Choose clean food, organic if possible. Good-quality produce is less likely to be contaminated with undesirable microorganisms that could compete with or inhibit the growth of beneficial lactic acid bacteria (LAB).
  • Be Consistent. Using consistent, high-quality produce helps maintain consistency and predictability. Variations can affect fermentation outcomes, leading to inconsistent results.
Understanding the Risks Exploring the Dangers of Lacto Fermentation, image with various jars and ingredients to ferment

How do you know if lacto-fermentation is working?

New to fermentation and wondering if you’re “doing it right”? Look for these signs. 

  • Bubbling and Gas Formation: One of the most noticeable signs of lacto-fermentation is the production of bubbles or gas. As the LAB consume sugars in the food, they produce carbon dioxide as a byproduct, leading to bubbling or fizzing in the fermenting mixture. This is especially visible in jars or containers with an airlock or a loose-fitting lid.
  • Change in Color: Fermenting vegetables, such as cabbage in sauerkraut or cucumbers in pickles, may undergo a change in color during lacto-fermentation. This can range from a vibrant hue to a duller, more translucent appearance. You may also see a cloudiness in your brine. 
  • Tangy Aroma: Lacto-fermentation produces a distinctive tangy or sour aroma as lactic acid accumulates in the fermenting food. This aroma becomes more pronounced as fermentation progresses. 
  • Taste Testing: Sampling the fermenting food allows you to gauge its progress. Over time, the sugars are converted into lactic acid, resulting in a tangy or sour taste. I like to start tasting the ferment after three or four days to monitor its flavor development. 
    • Be cautious not to introduce contaminants by using a clean utensil for sampling.
  • Texture Changes: Depending on the type of food being fermented, you may notice changes in texture. For instance, vegetables like cucumbers may become softer or more tender as they ferment. This texture change is a result of enzymatic activity and microbial fermentation.
  • pH Monitoring: Lactic acid fermentation typically lowers the pH of the fermenting medium due to the accumulation of lactic acid. Using pH strips or a pH meter can help monitor this change. The optimal pH for lacto-fermentation is typically below 4.6, which inhibits the growth of harmful bacteria.
    • Just remember, when in doubt, get a test strip out! 🙂

I hope you feel well equipped to take on your home fermentation experiments, and confident to avoid any lacto-fermentation dangers.

Finally, if you want to learn the best tips to ferment any vegetable, every time, check out my blog with the 11 Tips to Ferment Vegetables Safely, it includes a recipe.

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