What Makes Sauerkraut Sour?

How is sauerkraut made? Learn the ins and outs of how to make sauerkraut, including the secret of what makes sauerkraut sour.

You can find sauerkraut almost everywhere in America. If you’re in a major city, you can probably buy a hot dog smothered in the stuff (though, before I get letters, no sauerkraut taints a Chicago dog). Many restaurants have a Reuben (a sandwich claimed by both Omaha, Nebraska, and New York City) on the menu, and, if neither of those appeals, just head to any German household for great bratwurst and kraut. But how is sauerkraut made? Why do you make it in a crock? And just what makes sauerkraut “sour,” anyway?

Sauerkraut (German for “sour cabbage”) is part of a whole family of fermented foods that we enjoy (such as beer, yogurt, bread, wine and cheese). Though “fermented cabbage” may not have an appetizing sound, it has a storied history – enjoyed by the Romans, the Chinese who worked on the Great Wall, the Mongols and, of course, my German ancestors. Eventually, Dutch sailors discovered that serving it shipboard helped prevent scurvy (because of its vitamin C content). Sauerkraut packs a nutritious punch, containing vitamins C, B and K, riboflavin, iron and many others. Cabbage is more nutritious after it’s been fermented than when fresh.

Creating sauerkraut requires only a couple of ingredients – cabbage and salt. Usually, you don’t even need to add water because the salt pulls liquid out of the cabbage. The beasties that do the fermenting, Lactobacillus species of bacteria, don’t have to be added to the mix because they’re already present on the cabbage (and pretty much everything else – especially things that grow close to the ground). Lactobacilli are very friendly for humans: L. acidopholus is involved in making yogurt, and L. sanfanciscensis makes sourdough bread sour. For sauerkraut, we’ll be making use of L. plantarum.

How to make sauerkraut is simple. Shredded cabbage is layered with salt in a crock or other nonreactive container (like a food-grade plastic bucket), and then carefully packed to aid in pulling the liquid out and to remove as much air as possible. Once enough liquid is present to cover the cabbage, a weighted plate that just fits inside the crock, or even a plastic bag filled with water, is added to keep the cabbage from floating to the surface. The goal is to create an oxygen-free environment that is relatively inhospitable to the bad bacteria, so that we can encourage the bacteria that will convert the sugars and starches in cabbage to lactic acid. The temperature for this reaction is critical. If it’s too warm, other forms of bacteria and yeast are able to grow. The best kraut is made at cooler temperatures (65 degrees or lower), which is why we so often associate it with fall (and Oktoberfest).

Sauerkraut is all about the lactic acid. The acidic environment it creates preserves the cabbage by inhibiting the growth of microbes that cause rotting. This acid content also reacts with metals; hence we use a crock and a wooden spoon to keep the kraut safe from discoloration and leeching. But lactic acid does more than preserve, it’s also good for you and helps keep your intestines healthy. Last but not least, it’s the lactic acid that makes sauerkraut sour.