Will My Fermented Food Kill Me? Fermentation FAQs

I love teaching fermentation workshops and answering the many questions attendees ask me. Here, I’ve tried to address most of the common questions I hear but may have missed one or two. If you have a burning question about fermentation that I haven’t included, please ask away and I’ll do my best to answer.

This post focuses on vegetable or fruit ferments, such as:

Dill pickles
Hot peppers
Preserved lemons
Sauerkraut, plain
Sauerkraut, garlic-dill
Scrap vinegar
Watermelon rind pickles

For kombucha FAQs, go here.

Will I accidentally poison my family?

Over the years, people have told me their fear of fermentation has put them off of the idea. They worry they will mess up and get sick—or worse. Fermentation is actually extremely safe. In a vegetable ferment for example, the lactic acidic bacteria creates such an inhospitable, acidic environment, that any bad bacteria that find their way into it, die. So yes, you may kill living things, but only on a microscopic level. Just as with any other type of food preparation, use sanitary methods when you ferment food. Wash your hands, your equipment, your work surfaces and your produce before you start.

You say fermentation, I say pickling. Aren’t they the same thing, you pedantic English major?

These two food preservation techniques both result in a vinegary, pickle flavor but use different methods. The shelf-stable pickles you buy at the grocery store—the ones you’ll find in a center aisle—are cucumbers preserved in vinegar. Fermented cucumbers have been submerged in a salt-water brine, where the lactic acid bacteria present on the vegetables naturally produce an acidic, vinegary flavor. The result is a probiotic “pickle” and a live culture.

I have neither the time nor desire to turn my kitchen into a hippie food lab. Can I just buy probiotic pills?

To consume your microbes, you could buy these pricey supplements, however most companies manufacturing them stick with strains they know are safe—the ones found in fermented foods, which we have eaten for thousands of years. However, a one-size-fits-all commercial probiotic will not work for everyone’s unique microbiota. As researchers Justin and Erica Sonnenburg explain in their book The Good Gut:

Presently, our understanding of the microbiota is not complete enough to predict what specific effects a particular probiotic could have on an individual’s microbiota. For this reason, we feel that fermented foods, which contain a diverse collection of microorganisms, offer the best chance of encountering a microbe that will have a positive effect.

Of course, they don’t stipulate that you must eat homemade fermented food. If you don’t want to or can’t make it yourself, just buy it. If your supermarket carries fermented foods such as dill pickles, kimchi, kefir and kombucha, you will find them in the refrigerator section of the store and not in the center aisles of shelf-stable food.

Is my kitchen too cold? Too hot? Just right?

I have never used a heat mat under or heat wrap around my jars during fermentation. (I have knit sweaters for my sourdough starter Eleanor, but for fashion not function.) I avoid buying special equipment to ferment food and use just basic tools that almost everyone has in their kitchen.

However, if you do have a cold kitchen, your food may not ferment at all or it may ferment very slowly. In that case, find a warmer spot—the top of the refrigerator, near a pilot light, on a high shelf, in a closet—to speed up the fermentation. If your kitchen is very warm, your food will likely ferment quickly. In hot weather, sauerkraut, for example, may become mushy. To slow down vegetable ferments, use more salt—but not so much that you dislike the taste (and if you do accidentally add too much salt, add more vegetables or even water to dilute it).

Think of your jar of kraut as something of a thermometer. If the room is the right temperature (about 70ºF), your food will ferment. A little too cold or too warm and it may simply need you to make some minor adjustments. Your ferment will let you know.

Will you lend me the money to buy all the fancy equipment I need to start?

People have fermented food for thousands of years, long before consumer culture came along, convincing many of us all that we need special gadgets—and special training—to feed ourselves. As I mentioned above, you do not need special tools to get started. I know some people swear by their air locks, fancy glass weights, wooden pounders and thermometers. (I’d be surprised if you can’t find a thermometer with an app that alerts you of every slight temperature fluctuation.) I’m sure these tools are all very lovely but I own none of them. I am cheap. I am lazy (I hate cleaning additional tools). I have no space in my tiny kitchen for more stuff.

To ferment vegetables, you need a knife, a bowl and a jar. For kombucha and other fermented drinks, you may want to splurge on a few flip-top bottles and a nice funnel. Those are the fanciest pieces of fermenting equipment I own. Well okay, I do have some fancier stuff for sourdough bread but you don’t need those either.

Can I stick a fork in it to see if it’s done?

I get this question frequently. You don’t want to ferment your vegetables or beverages in metal containers as the acids developed in the ferment can react with metal. However, in my experience, just inserting a metal utensil into your concoction momentarily to taste it won’t harm it.

I can’t ferment in metal? What about plastic?

I don’t ferment anything in plastic and not simply because I hate the stuff and own very little of it. Plastic, when it comes into contact with acidic foods such as your ferment, can leach nasty chemicals into your food. Use glass or ceramic. I use glass jars most often but also the ceramic crock from my slow cooker—without the base! You don’t want to heat up your ferment. Heat will kill the microbes necessary to ferment the food.

For recipes calling for water, must I use bottled?

Please don’t. Bottled water wastes an obscene amount of plastic. Tap water should be fine. If your tap water contains high levels of chlorine—you will smell it if it does—the microbes in your ferment may die. To dissipate chlorine in tap water, several hours or the day before you make your ferment, pour some into a vessel and leave open to the air. Although I have not had this problem myself, I have read about it and like to make readers aware of it. 

Must I buy organic vegetables for my ferment?

I do buy organic ingredients but fermentation will work with non-organic ingredients with the exception of ginger-based recipes. Non-organic ginger may be irradiated, which kills the naturally occurring microbes necessary for the fermentation. For pickled ginger or ginger beer, choose organic ginger. The small amount of ginger in a recipe such as kimchi may be non-organic. A little bit of non-organic ginger, lacking the good microbes, should not affect your cabbage.

What kind of salt do you use?

Non-iodized sea salt contains many beneficial nutrients so I use that. Any salt with do though. I live near San Francisco and can buy salt from the San Francisco Bay locally. I like it a lot.

Shouldn’t I take one of your workshops before I attempt my first ferment?

I hate to put myself out of business but honestly, you really need only to read a few posts on fermentation or to get your hands on a copy of The Art of Fermentation by Sandor Katz (a.k.a. Sandorkraut). However, having someone show you the ropes certainly flattens out the learning curve. My first batch of sauerkraut turned out a mushy mess. I don’t think I had actually read a recipe for it and I just winged it. For my sourdough bread, I taught myself and took an embarrassingly long time to produce my first decent loaf of bread. Eventually I did it though.

You keep stressing that I MUST submerge all the vegetables in liquid. How do I do that?

Truly, the only trick to successful fermenting is to ensure you submerge your vegetables or fruit in liquid. The bacteria that ferment the food are anaerobic and will not reproduce unless you cut them off of oxygen (they’re kinky little bugs). When I ferment vegetables, I lay a cabbage leaf or grape leaf over them in the jar. I then put a small jar on top of the leaf. When I close the lid of the main jar, the small jar pushes the leaf and vegetables down and the liquid rises, submerging everything perfectly.

The top of my kimchi has turned brown and mushy. Should I throw it out?

Sounds like you haven’t submerged your vegetables completely in liquid. Scrape off the mushy brown layer and compost it. The vegetables below will be fine. Make sure the remaining vegetables are properly submerged.

My kimchi in the refrigerator is no longer submerged in liquid. Should I throw it out?

Once you have transferred your fermented food to the refrigerator, the fermentation process will grind to a near halt. At this point, you don’t need to worry about keeping the vegetables completely submerged in liquid. Your ferment will keep in the refrigerator for many months, if not longer. However, as you eat the food and create more space for air in the jar, you many want to move your food to a smaller jar. The less contact it comes into with the air, the crispier it will remain. But don’t worry too much about this.

I followed your kraut recipe and my cabbage hasn’t rendered enough liquid to properly submerge it. Should I throw it out?

Good lord, stop asking me if you should throw out your food! Have you not noticed my blog name at all? Zero-Waste Chef? Simply pour enough water over top of the vegetables to submerge everything. If you need more than a few tablespoons of water, make a brine and pour that on. Use approximately two teaspoons of salt per cup of water.

My ferment was completely submerged and now it isn’t. What should I do?

Most likely you just need to shove everything back down. When I make fermented salsa, the vegetables always float to the top of the jar, leaving most of the liquid at the bottom.

The water in my jar has turned cloudy and the vegetables have changed color. What’s wrong?

These both signify successful fermentation. Congratulations and enjoy your delicious food.

How do I know if my food is fermenting?

Within a day or two of starting your ferment, it should start to show signs of life—bubbling and gurgling and possibly oozing out of the jar a bit, depending on how high you filled it. Within three days, the flavor will have begun to turn vinegary.

When will my ferment be ready?

One of the many charms of fermentation is its flexibility. Most recipes consist of loose lists of ingredients that have many possible substitutions, imprecise measurements, suggestions rather than instructions and a wide range of wait times. How do you know if your sauerkraut is ready? Simply taste it. Like it? It’s done. Eat it all up or transfer it to the refrigerator. If you want it more sour, let it ferment longer.

I see black, white or green furry raised blobs on top of my ferment. Should I throw it out?

Okay, this time you are onto something… Fortunately I very rarely encounter mold but every time I peer into certain ferments, such as liquids, I brace myself for this horror. If you find white mold, according to Sandor Katz, you can simply scrape that off and eat the food underneath. But he warns not to eat food that has developed mold of other colors, as it has become more entrenched and can make you sick. In this case, you must toss the entire batch of food. 


You’ve scored some beautiful, juicy, fresh picked lemons, prepared them for their jar, taking care to add just the right spices, checking on them daily for the first week or so, only to discover that a thin matte layer of white film has developed on top of them. You’re heart sinks at the sight of what you assume is mold. Don’t toss out that ferment! Most likely, you have encountered your first—and not likely last—invasion of kahm yeast. Your ferment may smell yeasty or cheesy but kahm yeast is not mold.

Many of my batches of beet kvass have developed kahm yeast, a harmless invader that tends to form in ferments of sweeter vegetables. I have always simply scraped off as much as possible. I can never get it all and when it inevitably reappears in the batch, I scrape again and continue with my ferment as usual, eventually gobbling it all up and surviving to tell the tale. To help prevent kahm yeast from forming, try adding more salt to the ferment, or start your ferments in a cooler location. And always begin with clean equipment.


13 Replies to “Will My Fermented Food Kill Me? Fermentation FAQs”

  1. Hi Anne-Marie! I love reading your blog – no nonsense, easy to follow and craftily written. I recently got into fermentation (yeah, about three days ago when I purchased my first kefir grains and sourdough starter – that recent) so I am really enjoying reading all the advice you have to offer! Especially, how to not have my life taken over by it :))) THANK YOU.

    1. The Zero-Waste Chef says: Reply

      Thank you so much. I really appreciate that. Glad you hear you’ve caught the fermentation bug. It’s so fun. So many ferments to try… Yes, the starters can take over your life! They are like pets. I have three right now (I accidentally killed my buttermilk), in addition to things like kimchi and lemons, and that’s about all I can handle. Enjoy your fermenting adventures! ~ Anne Marie

  2. This is a great post! i’ve never personally tried fermented watermelon rinds but I think that is going to be next on my list to experiment with! It seems so interesting and not something you normally see in a household. Thanks for the informative article!

    1. The Zero-Waste Chef says: Reply

      Thanks for checking it out. If you add lots of garlic and dill, you might get that delicious Bubbies flavor 😉

  3. Need advise on fixing my very first batch. On the next day I realized that I put 20% salt, instead of recommended 2%. Is there any way to fix this horrific miscalculation? Thank you.

    1. The Zero-Waste Chef says: Reply

      Hi Alexandra. What did you make? Sauerkraut? You could fix it by adding a huge amount of unsalted vegetables until you have reduced to saltiness to the amount you like. You will LOTS. But it will work. ~ Anne Marie

  4. Hello, Anne-Marie. First of all, I love your blog and insta 🙂

    I want to start fermenting (thanks to you) and I have an important question: how should I wash the vegetables? We usually soak them for about 10 minutes in a chorine bleach solution, but would it kill the bacteria that are necessary for fermentation?

    Thanks in advance,
    ~ Tsuki

    1. The Zero-Waste Chef says: Reply

      Hi Tsuki,
      Yes, the bleach may kill the good bacteria you need to ferment your food. Washing them in a solution of baking soda and water will remove dirt and if you let them soak for a while, breaks up some pesticide residue: https://zerowastechef.com/2018/07/10/ditch-produce-wash-use-baking-soda-water-instead/
      I hope that helps.
      ~ Anne Marie

  5. […] Fermentation FAQ’s: This is a wonderful resource with many common fermentation questions. […]

  6. Hi,
    This is a very interesting post to me because I have a weak immune system (have had cancer and other medical problems) and would like to eat more fermented foods, although I haven’t tried making my own. However, my question here is about some ketchup I’ve been buying recently. I have stopped buying the “regular” brands and switched to an expensive American brand. Ingredients listed are: tomatoes, tomato concentrate, vinegar, molasses, balsamic vinegar, bourbon, bell peppers, as well as a number of herbs. I have never kept any sort of ketchup in the fridge, but this one states it should be refrigerated. At first, after purchasing this product I did not bother refrigerating, until I noticed a “whoosh” sound when opening a bottle. I did eat it although I was worried, and threw the rest out. Now, with new bottles, even though I do put them in the fridge, I am still getting a small hiss when I open them, especially if I shake the bottle slightly. So, question is–is this ketchup just fermenting a bit? Or is there some sort of bacterial buildup I should be worried about?

    1. Hi Louisa,
      It sounds to me like it is fermenting. I find tomatoes ferment quickly and then can turn alcoholic from all the sugar in them. Does it smell or taste at all alcoholic? Back when we bought ketchup, we bought the stuff in the plastic bottle and I don’t remember it fermenting but it’s SO processed. Your fancy stuff sounds more like real tomatoes that can ferment. If you’re worried though, I wouldn’t eat it. I’m sorry I don’t have a definitive answer.
      ~ Anne Marie

  7. This really helped me – I’m a newb and didn’t know that the brine drops below the top of sauerkraut. I was a little scared to eat it but as you said, the lactic acid has reached a high enough concentration that molds and yeasts can’t grow on the exposed surface. THANK YOU!

    1. I’m so glad this was helpful. Thank you for letting me know. Enjoy your fermented goodies!

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