Vinegar is an acidic liquid that is commonly used for cooking, cleaning, and even as a natural herbicide. While vinegar itself does not support much microbial life due to its acidic nature, there are a few notable things that can grow in vinegar under the right conditions.
Mother of Vinegar
Perhaps the most well-known organism that grows in vinegar is called “mother of vinegar.” This is a slimy, glistening microbial biofilm that forms on the surface of vinegar during fermentation. The mother of vinegar is a symbiotic culture of acetic acid bacteria (such as Acetobacter aceti) and yeast. The bacteria consume alcohol in the vinegar and produce acetic acid, increasing the acidity. Meanwhile, the yeast converts sugars into alcohol to feed the bacteria. Together, they live together in a self-sustaining ecosystem.
Mother of vinegar forms when there is oxygen present, allowing the aerobic acetic acid bacteria to thrive. It often appears as a hazy film covering the surface of vinegars like apple cider vinegar. The mother can also settle on the bottom of bottles or jars of vinegar in the form of cloudy strands or clumps. While the mother may look unappealing, it is completely harmless and a sign of a naturally fermented vinegar. The mother can be filtered out or blended into the vinegar to distribute the bacteria and yeast.
Mold
If vinegar is exposed to air, there is a chance mold can start to grow, especially if the acidity level drops over time. This is more likely to occur with homemade vinegar compared to commercially processed and sealed vinegars. Molds that can grow in vinegar include species of Aspergillus, Penicillium, and Mucor. They form visible furry colonies in a variety of colors, like black, green, grey, or white. Consuming moldy vinegar may cause allergic reactions or other health issues in sensitive individuals.
To prevent mold growth in vinegar, it helps to use vinegars with higher acidity like distilled white vinegar or cider vinegar. The acidity creates an inhospitable environment for most molds. Also, keeping vinegar bottles sealed and storing them in a cool, dark place inhibits mold growth. If mold does develop, it’s best to discard the vinegar.
Wood Ear Mushroom
The jelly ear or wood ear mushroom (Auricularia auricula) is an edible mushroom that can be intentionally grown in vinegar. It forms a gelatinous, ear-shaped fruiting body and thrives on acidic, sugary substrates. To cultivate wood ear mushrooms at home, place wood ear mushroom spores or spawn in a mixture of water, vinegar, and brown sugar heated to 160°F (71°C). Within a few weeks, rubbery mushrooms will form that can be harvested and eaten.
The acetic acid in vinegar helps trigger fruiting body formation in the wood ear fungus. The sugar provides nutrition. Wood ears grown in vinegar take on a tangy flavor and tender texture. Other vinegars like rice wine vinegar or balsamic vinegar can also be used. Wood ear mushrooms contain fiber, vitamins, and antioxidants and make a nutritional addition to soups, salads, and Asian dishes.
Kombucha SCOBY
Kombucha is a fizzy, fermented tea drink. It’s made by culturing green or black tea with a kombucha culture, known as a SCOBY. SCOBY is an acronym for “symbiotic culture of bacteria and yeast.” The kombucha SCOBY looks like a thick, rubbery pancake floating at the top of the tea. It’s a living colony of yeast, bacteria, and sometimes mucilaginous strands. The main bacteria are various species of Acetobacter that produce acetic acid, lowering pH and giving kombucha its sour taste.
To brew kombucha, the SCOBY is placed in sweetened black or green tea. As it ferments, the SCOBY produces organic acids like gluconic, acetic, lactic, and glucuronic acids that increase acidity and generate carbonation. The SCOBY grows larger with each successive batch as the cellulose-producing bacteria multiply. New layers form on its surface. Kombucha SCOBYs can survive andreplicate in the acidic environment created by the organic acids they produce. The finished kombucha can contain beneficial probiotics and is consumed as a health tonic.
Mycobacteria
Acid-fast mycobacteria are a group of bacteria that can tolerate acidic environments. This includes species such as Mycobacterium tuberculosis, the cause of tuberculosis, and Mycobacterium leprae which causes leprosy. While most bacteria cannot survive pH levels below 4, mycobacteria have specialized mechanisms that help them withstand acidity.
For example, mycobacteria have a thick, waxy, hydrophobic cell wall that helps exclude acids. They also utilize urease enzymes to raise cytosolic pH levels and amino acid decarboxylases to consume intracellular protons. This enables some mycobacteria to persist in acidic environments like vinegar. In one laboratory study, M. tuberculosis remained viable for over 12 months in vinegar with a pH as low as 2.5. However, vinegar’s antibacterial properties can help control the spread of mycobacteria on surfaces when used for cleaning.
Vinegar Eels
Vinegar eels are tiny nematode worms that feed on the bacteria and yeast found in vinegar. The scientific name is Turbatrix aceti. They are the only helminth species that can survive the acidic environment of vinegar. Vinegar eels measure just 0.04-0.2 inches (1-5 mm) long. They wiggle their slender bodies in a worm-like fashion but are not considered parasitic.
Under a microscope, vinegar eels appear transparent with a body cavity clearly visible. They have a pointed head and tail. Vinegar eels reproduce rapidly, going from egg to adult in only 3-5 days. A vinegar eel infestation may occur if vinegar is exposed to air, allowing the worms’ eggs to contaminate it. Heating vinegar to 150°F (65°C) for at least 15 minutes will kill vinegar eels and their eggs.
Fruit Flies
Fruit flies are attracted to vinegars, especially fermenting vinegars like apple cider vinegar. The acetic acid smells reminiscent of overripe fruit to fruit flies. They are drawn to lay eggs on or near vinegar. Tiny fruit fly maggots will hatch and crawl into the vinegar to feed. Common culprits include the apple cider vinegar fly (Drosophila melanogaster) and the spotted wing drosophila (Drosophila suzukii).
To prevent fruit fly infestations, it’s important to store vinegar in tightly sealed containers. Any vinegar with signs of flies or larvae should be discarded. Traps can also capture adult fruit flies using vinegar as bait. While the flies themselves can survive in vinegar temporarily, the acidity kills fruit fly larvae and eggs over time.
Acetic Acid Bacteria
Acetic acid bacteria are the primary bacteria responsible for converting alcohol into acetic acid during vinegar production. Major genera involved in vinegar making include Acetobacter and Gluconobacter species. They are gram-negative, aerobic bacteria that thrive in the high acid, low pH environments found in vinegar. Acetic acid bacteria can survive pH levels as low as 2.5.
Acetobacter species directly oxidize ethanol into acetic acid and water. Gluconobacter species indirectly produce acetic acid by first oxidizing ethanol into acetic aldehyde, which is then further oxidized into acetic acid. These metabolic processes also generate energy for the bacteria. Both genera also produce enzymes like cellulase that contribute to the increase in acidity during fermentation. Acetic acid bacteria are sometimes added directly as a starter culture when manufacturing vinegar to enhance the fermentation process.
Drosophila Fly
Several species of small flies belonging to the Drosophila genus are known to infest vinegars. These include the common fruit fly (D. melanogaster), spotted wing fly (D. suzukii), and apple cider vinegar fly (D. busckii). Female flies are strongly attracted to the smell of acetic acid produced during vinegar fermentation as it indicates a suitable environment for laying eggs.
Eggs are laid on or near vinegar substrates. After hatching, larvae crawl into the vinegar to feed on the bacteria, yeasts, sugars, and proteins within. The acetic acid in vinegar can eventually kill the larvae if the infestation is significant and pH drops low enough. But some larvae may successfully pupate and emerge later as adult flies to repeat the cycle.
Preventing exposure to oxygen and sealing vinegar storage containers helps deter flies. Traps can also capture adults using vinegar as bait. Heating vinegar to 150°F (65°C) for 15 minutes will kill all fly eggs and larvae. Maintaining vinegar acidity below pH 4 will inhibit future generations.
Vinegar Nematodes
Vinegar nematodes are microscopic worms that can tolerate the high acidity of vinegars. The dominant species found thriving in vinegars is Turbatrix aceti, commonly called the vinegar eel. Vinegar nematodes are thin, transparent worms measuring just 1-5 mm in length. Despite their name, they are not considered parasitic.
Nematodes feed on bacteria and yeast in vinegars, helping keep populations in check. They reproduce rapidly, going from egg to adult in 3-5 days. An infestation may develop if vinegar is exposed to air, allowing nematode eggs to contaminate it. Heating vinegar to 150°F (65°C) for 15 minutes will kill all life stages. Sealing vinegar storage containers helps prevent future nematode issues.
Conclusion
While vinegar’s acidic nature prevents most microbial growth, a few organisms have adapted to survive in it. The most common are the mother of vinegar biofilm, various molds, acetic acid bacteria, fruit flies, and vinegar eels. Keeping vinegar properly sealed, maintained at a low pH, and heating to kill contaminants if necessary helps limit microbial growth and infestations. The organisms that do grow in vinegar play an important role in fermentation and acidification during vinegar production.
| Organism | Characteristics |
|---|---|
| Mother of vinegar | Symbiotic culture of yeast and acetic acid bacteria that forms biofilm on vinegar surface during fermentation. |
| Mold | Fungi like Aspergillus, Penicillium, Mucor that can grow in low acidity vinegars and spoiled vinegar products. |
| Wood ear mushroom | Edible Auricularia auricula fungus intentionally cultured in sweetened vinegar mixtures. |
| Kombucha SCOBY | Cellulose-producing bacterial colony that ferments tea into kombucha when cultured in the acidic beverage. |
| Acetic acid bacteria | Microbes like Acetobacter and Gluconobacter that can withstand vinegar’s acidity and produce acetic acid during fermentation. |
| Fruit flies | Drosophila flies attracted to fermenting vinegar to lay eggs, though larvae often die from acidity over time. |
| Vinegar eels | Turbatrix aceti nematodes that feed on bacteria and yeast in vinegar and help control their populations. |
