Sauerkraut: What Makes it Sour?

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.