Aerobic vs Anaerobic Fermentation Controversy

I hear that much controversy is brewing on the internet over vessels for fermenting vegetables, and the implications of whether or not they are totally anaerobic. I have made hundreds of batches of kraut in all sorts of vessels (most of them open crocks), and I have witnessed, consistently, that it doesn’t matter. Each vessel has advantages and disadvantages. No particular type of vessel is critical. People have been fermenting vegetables for millennia in crocks open and closed, in pits and trenches, in sealed and open vessels. It can be done many different ways. The only critical factor is that the vegetables be submerged under brine.

Whenever vegetables are submerged under brine, lactic acid bacteria (which are anaerobic) develop. Whether or not the vessel protects the surface of the ferment from atmospheric oxygen, the microbial development under the brine is anaerobic lactic acid bacteria. In the vocabulary of microbiology, lactic acid bacteria are “facultative” in that they that do not require oxygen, but are not inhibited by its presence; in contrast, certain other bacteria (for example Clostridium botulinum) are “obligate” anaerobes that require a perfectly anaerobic environment.

The only difference air exposure or lack thereof makes is whether aerobic organisms like yeasts and molds can develop on the surface. The barrel of kraut I have had fermenting in the cellar for six months now is good and sour, and I have been eating from it and sharing it widely for months. Each time I remove the cloth tied down over it, and the jugs of water weighing it down, and the two semi-circular oak boards that rest upon the surface, I skim off a moldy layer around the edges and down the middle, wherever the surface was exposed to air. I toss the moldy layer into the compost, and the kraut beneath it looks, smells, and tastes wonderful. Many people have reported how good it made them feel and not a single person has complained of any problems from it, ever. The brine protects the vegetables from the aerobic organisms that grow on the exposed surfaces. The ferment is a lactic acid ferment, even though the surface is aerobic. Surface growth should be scraped away because if it is allowed to grow it can diminish the acidity of the kraut and affect flavor and texture, but if you keep periodically scraping mold away, the ferment beneath is fine.

I have also fermented in Harsch crocks, Pickl-Its, Mason Jars, and many other types of vessels. Mason jars become highly pressurized if you fail to loosen them to release pressure. Even if they are not perfectly airtight, they permit little airflow. Many times I have witnessed carbon dioxide force its way through the airtight seal by contorting the tops to provide an escape for the pressure. The various air-locked designs that allow pressure to release while preventing air from entering the system are generally effective at preventing aerobic surface growth. Yet still I generally do not use them because I love to look at and smell and taste my krauts as they develop, and each time you open an air-locked vessel you defeat its purpose, allowing air in. The vessels are effective, but are not well-suited to my desire to taste at frequent intervals. Different vessels suit different needs and desires. No one type of vessel is essential for fermenting vegetables. I have had success using every type of vessel I could think of. As long as you can keep vegetables submerged, lactic acid bacteria will develop. The process is extremely versatile.

For more in-depth information on fermenting vegetables, fermentation vessels, and all realms of fermentation, check out my new book, hot off the presses, The Art of Fermentation. Keep fermenting….


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9 thoughts on “Aerobic vs Anaerobic Fermentation Controversy

  1. How important is darkness to a ferment? I like to use 2 qt Ball jars to ferment and sometimes I think allowing light into the ferment ruins it. What is your opinion?

    • I keep ferments out of direct sunlight because uv rays degrade nutrients, but I have never found that ambient light exposure inhibits the fermentation. In some traditions, peopl;e ferment in sunlight in order to inhibit surface molds. There are many ways….

  2. I’ve been making kraut for a few years now, always have it finished and in process. I’ve only ever used a food grade plastic round tub. I put a few brine filled plastic bags on top to weigh it down. Seems to work well but I’m curious what you think about this type of vessel. .

    • Functionally effective, though glass, ceramic (with unleaded glazes), and wood are preferable in that they are more stable and do not leach chemicals into food.

  3. Sandor,

    I must respectively disagree with your statement

    “Whether or not the vessel protects the surface of the ferment
    from atmospheric oxygen, the microbial development under
    the brine is anaerobic lactic acid bacteria”

    As you know fermentation, by definition, is anaerobic and the “facultive” bacteria will prefer “cellular respiration” (aerobic) when Oxygen is available as it is more efficient for the bacteria. This is true whether the Oxygen is in the brine or dissolved in the brine!

    Oxygen is dissolved in water/brine, and will continue to absorb if Oxygen is available (like open containers) through a process called “diffusion.”
    From the Archives of Microbiology: “Increased O2 utilization was accompanied by a switch in metabolism which resulted in acetate rather than lactate accumulation in aerobic cultures” Also, “The growth rate of Lactobacillus plantarum in a complex medium with 55.6 mM glucose decreased during aerobic incubation (relative to anaerobic incubation)”
    In other words, with Oxygen (even under brine) acetic acid (vinegar) will be produced rather than lactic acid and the growth rate of Lactobacillus is reduced in the presence of Oxygen. Again, it doesn’t matter if the Oxygen is dissolved in brine.

    As already mentioned, open containers can continue to absorb Oxygen. A further problem exists for sealed containers (no airlock). The reason is, as the pressure builds the free Oxygen in the airspace will migrate to the water! This is due to the fact that the air compresses more readily than water, and soon the water becomes more friendly for the Oxygen to move to.

    You are absolutely right to point out that releasing the pressure, or opening the container to taste defeats the purpose of a container with airlock. There are some people out there that mistakenly state that opening a container fast enough to release built-up gases won’t let oxygen back in. That is simply wishful thinking.
    In summary, not all fermenting containers are equal.

    Although there are certainly some tradeoffs, such as budget, or your desire to open to taste throughout the fermenting process, the ideal fermentation environment is hermetically sealed and has an airlock to release pressure without allowing Oxygen to reenter. The fact that food is under brine doesn’t change that.

    • All I can say is that I have made kraut for nearly 20 years in open vessels, and my kraut is always acidic and delicious. Submerging under brine offers enough protection from oxygen for a successful, healthy, and delicious ferment.

  4. Around 50% of lactic acid bacteria actually will do aerobic respiration if they have access to oxygen and to heme (they can’t make heme them self). But heme is not only present in e.g. meat, but also in plant material (in the cytochrome):

    DOI: 10.1146/annurev-food-022811-101255

  5. I have IBS-D (Irritable Bowel Syndrome-Diarrhea predominant). Currently I am only eating fully cooked vegetables. I cannot eat pickles at all (ascorbic acid is a no-no for my digestive system). I cannot take large doses of vitamin C, or eat/drink citrus fruit.
    I have had good results from the 14 day probiotic yoghurt challenge. I heard you on the radio, & I am interested in trying your digestive tonic. Although I’m primarily interested in the tonic, adding fermented veggies to my diet would open up a world of possibilities (fish tacos?).
    Even if it’s only an educated guess, I would appreciate your professional opinion on:
    1). Is it likely that my digestive system will respond differently to Lactic Acid, than the other acids?
    2). If I keep my fermenting space at a constant temperature (what temp?), where in the time line will the bennificial bacteria be significant, but the acid not too sour?
    3). If I rush it into the fridge at that benefit point, how long before the bacteria degenerate or the acid sours?
    4). If I separate the kraut from the tonic will the bacteria survive? Will the tonic last longer?
    I’m not afraid to experiment, so having this starting point is a huge benefit. Thank you for your expertise, and your fine work.


    • Lactic acid is different than acetic acid and your system may respond differently. You can enjoy your kraut after just a couple of days if you want to minimize sourness. The progression will be very slow in the refrigerator. Bacteria will survive in the kraut itself or in the juice.

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