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Food Safety Issues/possible bean soup fermentation


QUESTION: I made a large pot of ham and bean soup.  I used the a dry bean mix, navy beans and black eyed peas.  I used the fast soak method (bring to a boil and soak for an hour or so).  I rinsed the beans before adding them to the broth.  I added the potatoes and cooked for a few hours longer.  Once I turned the soup off, I partially covered the soup with aluminum foil and put it in the refrigerator.  The next day when I removed the soup from the refrigerator (about 18 hours later) it was frothy on top and in one particular section there were bubbles.  I thought is had a slight smell so I scooped the frothy part away and tasted the soup in the other section...thought it was okay to eat but now I am not sure.  I have made bean soup many times before but this has never happened.  Is the soup spoiled and we should not eat?  Also, do you have any idea why this may have happened.  Thanks.

ANSWER: Hi Carol,

Putting a large pot of soup in the refrigerator to cool can be a recipe for danger. When potentially hazardous foods such as cooked beans and potatoes are cooled too slowly they sometimes can ferment or worse, allow harmful bacteria to grow.  Placing a large mass of potentially hazardous foods within the "Danger Zone" -- 41 to 135 degrees -- for more than 6 hours can give bacteria the right environment for rapid growth.

From what you describe it sounds like your soup was in the process of fermenting. The fermentation process requires a warm environment and the right bacteria present. If you deny the warm environment by quickly refrigerating the soup in a shallow container (4 inches or less) the chances for fermentation to occur are very, very slim - if almost non-existent.

Any time there is an off flavor or unusual occurrence such as "bubbling" it is always wise to not consume the food, but rather pitch it.  While it may be just fermentation (which will not make your ill) it is possible that harmful bacteria that do not give off signals that they are present are also growing, thus the general recommendation is to pitch any food with visible quality changes.

In the future I suggest that you break the soup down into smaller containers and cool it in the refrigerator to a temperature of 41 degrees or below within 6 hours.



---------- FOLLOW-UP ----------

QUESTION: Just so I don't make the mistake again, this is happening even though I refrigerated the soup right away because I left it in a large pot which then took too long too cool.  Is that correct? I have made large pots of ham and bean soup before and this did not happen ( although the soup may have been cooler when I first put it in the refrigerator on the time.  Sorry for asking for clarification but I cook in large quantities often.  Thanks

Hi Carol,

As you found out, fermentation of your bean soup does not happen every time and only occurs when the right conditions are all in place. One way to minimize the chances of it ever happening again is to cool down the soup quickly -- from hot to 70 degrees F within 2 hours -- and then down to 41 degrees in an additional 4 hours.  The key is to divide the soup into smaller portions that are no more than 4-inchs deep.

Hope this is clearer and that you never have fermenting bean soup again.


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Carol Schlitt


I can answer questions on home food safety, sanitation and home food preservation.


I am a former Extension educator, nutrition, wellness and food safety, having retired August 1, 2010. I am a food safety instructor for the Illinois Department of Public Health, a ServSafe Instructor/Proctor and have my own company, Safe & Savory Solutions, Inc -

National Extension Association of Family and Consumer Sciences (Past President and current Historian), St. Louis Culinary Society.

BS - University of Illinois MS - Southern Illinois University at Edwardsville

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