Go Further

Fermented Food

Once you’ve developed an appreciation for the importance of the microbiome, you’ll want to become more of a farmer, growing your own symbionts.

Here are a few things to try:

  1. Fermented and pickled food
  2. Raw milk

People have been fermenting food since the distant past, making everything from beer to cheese. Fermentation is an ideal way to preserve food beyond the date at which it is practical to eat.

Fermenting your own foods is surprisingly easy.


One of the easiest ferments is home-made yogurt. Pour a few cups of whole milk into a saucepan and heat to not-quite-boiling. You’ll need to get it above 160 degrees, the temperature that kills bacteria in milk, but if it goes all the way to boiling the milk will taste scalded. Even that’s not the end of the world, but you may as well try to keep it under that. Use a kitchen thermometer the first few times if you like, but soon you’ll be able to tell intuitively because you’ll see steam rising from the surface of the milk, but no boiling bubbles.

After the milk has been heated, remove and pour it into a glass bowl. Let it sit until it cools to about 110 degrees. Here, a kitchen thermometer is more useful, especially the first time because the exact temperature is more important. Warmer than 110 degrees and the lactobacillus yogurt bacteria will die; too much lower and they won’t grow. Once you have the hang of it, you’ll be able to tell based on the touch: it’ll feel unpleasantly warmer than your hand (which should be 98 degrees) but not too warm to touch. Once the milk hits that rough temperature zone, pour in a tiny amount of yogurt from another source. This is called the “starter” yogurt and the best is to use a bit of leftover from your previous batch, but for your first attempt you can use any commercially-purchased yogurt. Sweetened, flavored, non-fat — any kind is okay as long as it has live cultures in it.

Be sure not to use too much yogurt. Definitely no more than a tablespoon, and perhaps even just a teaspoon or two. Because of the small amounts, you’ll be tempted to think you need more, but in this case more is definitely not better. Too much starter will suffocate the mixture. Whenever I’ve had an unsuccessful batch it’s almost always due to having too much starter.

Mix the starter thoroughly into the lukewarm milk and then cover it up and put it someplace warm. The key is to keep the mixture close to that magical 110 degree point. Some people put it overnight in an oven set to the lowest temperature, but if you don’t like running the oven overnight you can try wrapping it tightly with something that will retain the heat through the night. If have a high-quality thermos-style cooler, you can set it inside there, and some people cover it with thick towels and set it in the warmest part of the house. Another option is to use a heating pad, set to the lowest setting and placed underneath the bowl. The important thing is to keep the mixture at the warm temperatures that the bacteria need in order to breed.

Set in a quiet place for about 8-10 hours. Overnight is ideal. When you open the bowl again, you’ll find the mixture no longer resembles milk, but has been transformed into a much thicker consistency — a yogurt. It will taste sour, and if you’re not accustomed to plain, unsweetened yogurt you may even think that is has spoiled. Nope, that’s just how pure, real yogurt is meant to taste.


The next step after yogurt-making is also easy. It takes a little longer, from one to several weeks, but lets you expand your fermentation skills to many more foods. The most basic one is cabbage, to make your own sauerkraut.

Think of fermentation as a type of farming, only instead of large plants that you see, you’re farming with invisible microbes. In both cases the object is to start with a small seed that grows into a full crop. For sauerkraut, the microbes are naturally occurring on the leaves of plants and vegetables. You just need to put them into the right environment so the microbes can grow. Start with a small head of cabbage and a grater. If you don’t have a grater, then just chop it into small pieces. Cabbage is already covered with tiny microbes, but the interesting ones will not reproduce in the presence of oxygen; you need to get them out of the air. The best way to do that is to submerge them in a liquid — in this case we’ll use the naturally occurring water inside the cabbage leaves themselves. The purpose of grating or chopping is simply to let the water escape from the leaves until it covers the entire mixture.

You’ll need some type of container to submerge the leaves. Best is something made of glass or ceramic, though any container is fine as long as it doesn’t react with the acids that will be produced by the microbes. A standard mason jar works, for example, or even a cleaned-out jar of pasta sauce. Make sure you have a lid for the container, and make sure the lid doesn’t close too tightly. If you use something with a screw-top lid (like a pasta sauce jar) just pop a few tiny holes in the lid. The microbes will be producing carbon dioxide as they ferment, and you’ll need a way for the gases to leave or the container will explode.

Begin packing the cabbage leaves into the container as tightly as possible. While doing this, most people add some salt. The salt serves two purposes; it adds flavor, and it helps draw more water out of the plant. Just a small amount of salt is enough: about what you would use if you were seasoning it for flavor: a few shakes on each cabbage leaf as you peel it is enough, or maybe a total of a tablespoon or two for a small head of cabbage. Continue to pile more leaves into the container until it is full.

If you’re doing everything correctly, there will be a nice layer of liquid that completely covers the leaves in the container. Remember that the microbes can’t reproduce if there is air, so covering with liquid is essential. If you see any green leaves poking out of the liquid, pack them down further. It may help to find an insert of some kind to place directly over the leaves, perhaps anthe lid to a smaller sized jar, one that fits inside the container and lets you squish the leaves even tighter. The key is to keep everything submerged in liquid.

Put as many cabbage leaves as you can into the container and close the lid, but be careful: the bacteria in the jar will soon start to produce carbon dioxide gas, which will put pressure on the container. That’s the reason for the air holes you poked in the lid beforehand. You may want to cover the entire jar with a loose-fitting piece of cellophane, or an old cloth, as a precaution in case the aroma begins to attract insects.

That’s it! Leave the fermenting jar in a cool, undisturbed place and then check on it for the first few days. Make sure the liquid has entirely submerged the cabbage leaves. Within a day or two you’ll also notice some air bubbles in the liquid — the sign that the fermentation has begun to work. Now, just let the jar rest for another several days or more. The longer it sits, the more acidic it will become. If you like a sour taste, let it sit for a week or two, maybe even up to a month or more. If you want a more subtle flavor, take it out in a few days. Feel free to sniff the jar every day or two to decide when you think it’s ready.

When finished, it will look and smell like sauerkraut. If some of the leaves were not entirely submerged in liquid, it’s possible that a layer of moldy fungus has appeared, unsightly but not a problem. Just scrape off whatever doesn’t look like sauerkraut and eat the rest.

What’s happening in sauerkraut

The transformation from cabbage leaves to sauerkraut happens thanks to a complex interaction of bacteria starting with some members of the Leuconostoc species that occur naturally on the cabbage leaves. These are anaerobic organisms — they can’t live in oxygen. When submerged in the cabbage liquid, however, they thrive, consuming all the sugars they can find and converting them to lactic acid, giving off carbon dioxide as a byproduct. You’ll know the reaction is occurring when you spot tiny bubbles at the surface of the liquid a few hours after beginning the reaction.

Sadly for the Leuconostoc, they are too good at what they do. Eventually they’ll consume all of the sugars they find transforming the liquid into a sour concoction, and as result the environment turns too acidic for them and they die.

By then, the conditions have become ideal for another species, lactobacillus, which was pretty much designed for acidic liquids, and they finish off the remaining sugars, until the acidic level reaches PH=3, at which point their work is done. Fortunately for humans, the pathogens that could cause us harm are unable to survive in this high-acidic environment, and would be out-competed by the existing microbes anyway, so the final mixture is perfectly healthy.

More fermentation

Just about any food can be fermented, as people in all cultures have known since pre-history. Many common ethnic foods, such as miso (soybean) or kimchee (cabbage), are possible only thanks to fermentation. When you eat “cured” bacon or sausage, you are eating something that resulted from a complex interaction between microbes and meat.

[other inspired by Gerard Mullin:

Pickled Ginger

  • 1 tsp whole cloves
  • 1/4 tsp salt
  • 1/2 pound fresh ginger, thinly sliced

cover with water and leave on the counter for 3-7 days

Pickled cucumbers

•    2 TB chopped dill
•    2 cloves minced garlic
•    1 tsp mustard seeds
•    1/4 tsp salt
•    1/2 pound cucumbers in 1/2" slices

fill with water, cover with a cloth and leave for 3-7 days

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