This past summer, a housemate of mine lent me a book called Wild Fermentation, written by Sandor Ellix Katz and published by the Chelsea Green Publishing Company of White River Junction. It’s at once a recipe book, a history book, and a manifesto, all centered on the various microbial food-making processes known collectively as fermentation. Reading it was a revelation for me. Food and food preparation suddenly had a whole new dimension that I’d barely considered before.

Katz repeatedly touts the nutritional benefits of fermented food. Many foods become more digestible when fermented, and sometimes nutrients become available that are otherwise inaccessible. The living microorganisms in raw fermented foods like yogurt or miso take up residence in the intestines and promote a healthy immune system.

More importantly though, fermentation is fun. The process of fermenting something, particularly when one is not using cultivated microbes (a “wild” fermentation) is exciting and unpredictable, somewhere at the intersection of cooking, alchemy, and pet ownership. Through fermentation, basic foods gain amazing and idiosyncratic textures, flavors, and properties. Many of the most interesting fermented foods tend to be delicacies to one culture and noxious or rotten to another, whether the product in question is foul-smelling mold-riddled cheese, mucilaginous cultured soybeans, or corn liquor made with human saliva.
For thousands of years, fermented foods have been a major part of every agricultural and many non-agricultural societies. In pre-refrigeration days, their ability to keep for long periods of time made them invaluable both in hot moist climates where things rot quickly and in temperate climates where nothing could be grown for much of the year. Wild microorganisms like the ones that were used in the first fermentations are omnipresent and extremely diverse, and the makeup of the microbiological community differs vastly from place to place. This enormous diversity of life gave rise to a corresponding diversity of foods, the 256 cheeses of France being one example. (One of them, an egg-sized, rind-encrusted nugget, smells so awful that even the French call it “la crotte du diable”—“the devil’s turd.”) It is an unfortunate instance of cultural poverty that regionally specific, living food is largely absent (with a few notable exceptions) from modern American culture. Hopefully, with the growing popularity of local foods, regional cuisines will start cropping up in the United States.

My first foray into the world of fermentation (apart from baking bread) was to make yogurt. I was stunned to find how incredibly easy it was, how much cheaper, and how much more delicious. Previously I would buy yogurt to eat with granola. After I started making my own, I tended to just eat the yogurt plain, straight out of the container.

HOME-MADE YOGURT

Equipment:
- A pot big enough to hold as much milk as you want to turn into yogurt (one quart of milk makes one quart of yogurt).
- A non-metal container (preferably with a lid) for storing the yogurt.
- Some sort of insulation device. I use a Styrofoam medicine cooler that a co-worker gave me, and I fill it with a couple inches of warm water. Any sort of cooler will work, as well as an oven with a basin of hot water, a laundry hamper filled with clothes, a box filled with packing peanuts, anything that will keep the yogurt warm overnight.

Ingredients:
- Milk. Whole milk tastes best. Pasteurized milk is fine, but ultrapasteurized milk apparently doesn’t work because of the way the proteins are denatured in the pasteurization process.
- One tablespoon of yogurt per quart of milk. Make sure to use yogurt that is labeled as containing “active cultures.” This spoonful of yogurt contains a plethora of microbes bred for their ability to turn milk into delicious yogurt, similar to the way commercial bread yeasts are bred to produce lots of CO2. After you’ve made one batch of yogurt you can (if you’re good at planning) use a spoonful of the old yogurt to start the next batch. Every successive generation will taste progressively stronger and more unique, though, as the mix of organisms begins to incorporate wild strains along with the domestic ones.

Instructions:
- In the pot, heat the milk to nearly boiling (stop heating when little bubbles begin to appear). Stir often to prevent it from burning. This step is optional, but supposedly makes the yogurt thicker.
- Let cool until it is at about 110°F. You don’t need a thermometer. Just dip your (clean!) finger in the pot; if the milk is hot but not so hot that you can’t keep your finger in it for a couple seconds, then it’s probably about the right temperature.
- Mix in the tablespoon of live yogurt.
- Cover and put in your insulator.
- Let sit 8-12 hours. If you make the yogurt in the evening it should be done by morning. Try to move it as little as possible; yogurt doesn’t like to be jostled while it is forming.

Eating The Yogurt:
You can eat it now, although warm yogurt is a little bit bizarre, at least for breakfast. Anyway, when it has solidified (“yoged”) to your satisfaction, place it in the refrigerator. This does not kill the culture, only slows it down. The yogurt will slowly continue to get sourer as the days go by, as lactose is converted to lactic acid. It probably won’t truly go bad, in the sense of growing mold or becoming potentially harmful for a very long time—that’s why it was invented in the first place—but it’ll start tasting stronger than might be desired after maybe a week.