Soup Fermentation

The friendliest place on the web for anyone that enjoys cooking.
If you have answers, please help by responding to the unanswered posts.
Maybe the bubbles were from the beans and lentils, when you cook them the scummy, frothy substance sits on the top of the water, might have been this?
This question was asked years ago, but my mother had the same question for me......the answer simply lies in the potatoes. Potatoes are high in carbs (complex sugars) and starch. This is why potatoes are used to make Vodka! The sugars, in this case, reacted with the amylase found in the grains! Thusly, alcohol was produced and created a pungent, bubbly, flavor ruining effect!

simply put, if potatoes are added to a soup with grains it must be done so in the proper manner. (boiling potatoes before adding them to the soup!)
Call me skeptical, but I just ain't buying it.

I've been fermenting foods (on purpose) for well over 20 years. I make my own wine, sauerkraut, fermented hot sauces, bread, and occasionally cheese, and I can tell you that fermentation does not happen this quickly.

First of all, boiling the soup would kill any natural yeast or lactobacillus that happened to be in the soup or any of the ingredients added to it. Yeast is killed above 110°F and LAB at around 140°F. There are other bacteria that will survive higher temperatures, but those are not nearly as common.

Now sitting on the stovetop, the soup would eventually cool down to a temperature where bacteria and yeast in the air would begin to colonize again, but it would take longer than four hours and much longer with a lid on the pot.

But for the sake of argument, let's say that a colony of yeast did manage to make it's way into the soup. Once it got there, it would initially have nothing to eat. The previous poster mentions amylase, which is an enzyme that is present in flour and starts to break starch down into fermentable sugars once you add water. If there were flour used to thicken the soup, there would be amylase present. However, the problem is that amylase is destroyed by the cooking process.

If the OP added sugar to the soup, that would initially give yeast something to munch on, but I still find it unlikely that a feral yeast strain would colonize that quickly. And they do establish a colony before they begin metabolizing sugar. In winemaking, we call this the lag phase, and it can take anywhere from 6 to 12 hours - sometimes even longer.

So all of this makes fermentation highly unlikely. I'm not saying it couldn't happen, but I would look more for either a chemical reaction of some sort, or the possibility that something was added after the soup cooled that was possibly contaminated. Or the soup didn't cook completely or sat for longer than 4 hours. Or maybe the soup was simply not cooked at as high a temperature as the OP believes. Those are more likely scenarios.
Last edited:
You're certainly not a dummy.....but you are dwelling on yeast as the anaerobic agent where in this case I'm discussing the enzyme amylase.

Likely scenarios do indeed include sitting for longer then 4 well as being in a pressurized environ after having the lid slapped on.

Lets say the 4 hrs became 6 hrs.....and you mention that sugar needed to be added.....did you miss the fact that starch is sugar? Or that there are certainly enough possibilities for chemical reactions when creating a soup??

Amylase converts starchs into sugars. Bro.
Plus, there's always botchulism


I reread your post and see you mention amylase and its breakdown of starches.....

Amylase is present in grains, wheats, saliva etc....
And amylase is destroyed by the cooking process... as I pointed out in my post. 10 minutes at 175°F. Bro.

As far as I have seen through my experiments, many enzymes including amylase do not denature until they are above 212°F. If in fact the OP boiled his soup, which is not common to do except in the very early stages of creating a stock, than perhaps all of the amylase was destroyed. It is also common to add your grains to the soup at the end of the simmer after all veggies have been cooked and the soup has been allowed to reduce. Partial denaturing is quite plausible, but one must remember that no chemical reaction is 100% efficient until catalyzed. Even if a catalyst is used, the reaction never reaches 100% efficiency.

My postulate remains...........the starches and sugars in the veggies remained in solution until the amylase was added to the solution at which point the starch was further converted to glucose. This high sugar solution was left out at a moderate temperature cooling quickly due to the high surface area of a stove pot and was set into a pressurized container into the fridge. Also, as you have stated, perhaps the OP didn't cook at a high temperature. :cool:
Welcome to DC, notachefjustagoodcook! What an interesting way to start off - people don't usually join the forum by arguing about an almost four-year-old thread, so why don't you head over to the Introductions section and tell us about yourself? :)
Soured Soup

Misery. I just has to toss two gallons of my $eafood chowdah because it turned sour overnight.

I don't think it had to do with storage; it's the second time I've had this happen when using Yukon Gold potatoes [the first was with a beef stew]; this time I was sure to fully cook them separately before adding to the soup. But it happened anyway.

It definitely was fermentation going on and I can't think of anything else among the ingredients which might have caused this calamity.
Soured Soup

Misery. I just has to toss two gallons of my $eafood chowdah because it turned sour overnight.

It definitely was fermentation going on and I can't think of anything else among the ingredients which might have caused this calamity.

You may be right, potatoes, mostly starch, the perfect food for fermentation. I'm so sorry to hear of the loss of the seafood chowder, honest. Seafood in the midwest US is expensive and hard to come by and I imagine 2 gallons, a feast like that, would be a tough loss! It would be for me. Merry Christmas or Happy Hanukkah or best wishes, on this special day.
So I came across this thread as a result of something similar happening to me, but it wasn't fermentation or bacterial activity. It was because I used really hard tap water and a particularly large amount of diced tomatoes in juice. The vitamin C in the tomato juice had reacted chemically with the limestone in the water to produce the carbonation. However, the palatability of the soup was pretty poor afterwards, as it turns out that the other product of said reaction, calcium ascorbate, has a fairly acrid taste and smells pretty bad.
Last edited:
From the desription of smell,, and flavor, I would suspect yeast spores from the air, the same wild yeast ised to create sour dough, sour kraut and apple wine.
It grows very quickly and would account for the effervecnce and sour flavor
That's my best guess. In any case. I am sorry your soup was comtaminated. There are lots of nutrients with the barley, and beans to feed wild yeast.

Seeeeya; Chief Longwimd of the North
Last edited:
I don't know whether this is the best place to post about this or should I start a new topic. But I have a similar problem:

I cook for my dogs once a week. It is a form of thick stew that has some basic ingredients: Meat, Chicken liver, heart, gizzards, Ground beef, Brown rice, Quinoa, Red Lentil, Broccoli, Kale, Peas, Carrots, Squash, Mango, Flaxseed, Chia seed.

I have been making this stew for years...once a week...always the same ingredients with some minor ingredient changes.
The food is cooked within roughly 4 hours in an oversized extra large pot. I start the heat at boil and then reduce to medium heat until it is fully cooked. After it is fully cooked I turn off and leave on the stove until it cools down. Because it is such a large pot, it takes a while for it to cool down....around 6 hours.
Everything was fine until a few months ago.
The past few months, after i cool down the stew and pack it in the plastic containers in the fridge (fridge is set on the highest cold. The top shelves freeze), I place the containers on the middle shelf....That is the only place that can hold the containers.

There is where the problem begins.

The stew starts liquifying and when I spoon through it, fine bubbles come to surface. The liquid separates and flows out of the containers. So much so that it flows and leaks out of the fridge. My thick and nicely set stew becomes watery and the extra fluid is all leaking out.
The fridge is cold enough that the leaked out juice freezes on the base of the I know the stew is not under low temperature and it doesn't smell like bad food. It just has the strong smell it should have.

When this happened the first time, I threw out the stew...the second time...I threw out the stew...the 3rd time,...I kept it and ate some to be sure it is okay. When i didnt get sick, I fed it to my dogs. They are okay...I am okay...but no matter what I do, my food leaks out.

I have packed earlier, when the stew was still hot....I have packed later, when the stew was completely chilled and cool,...all the way. I have packed and stored in warmer colder fridge...nothing I do changes anything at all.

I am so frustrated. I don't know why this is happening. I am guessing it is a form of fermentation. I am sure there is no growth of yeast on the surface, as that white film does not appear.

I am an experienced cook and this food I make for my dogs is not new....but only since the weather started changing this year, and the temp dropped we have had this issue. My house is generally quite cold. No heat in the kitchen at all. I like it this way.

So sorry for the long post....I wanted to make sure I have given all the details.
Anyone can help me figure out what is happening?
This post is so wierdly specific to our own situation that I have joined the conversation. It echoes our predicament almost exactly!

We make our own dog food every 2 weeks and have done for the past year.. no issues.
Chicken, minced beef, chicken livers, carrots, blueberries, red peppers, brown rice, spinach, sweet potato and eggs. (Seeds and supplements added afterwards , not at this stage yet)

Never once... not once has this issue ever arisen.

Today, cooked it in a huge pot, moved to the chiller as usual and within an hour its bubbling almost to overflowing and smells kinda sour.

Now everything was totally fresh so it's not bad and theres a chemical reaction going on evidently.. hut why now? Why never before.
Its so bizarre!
Glad we're not alone's reassuring.
Top Bottom