Acid Truths

How is food made sour? Let us count the ways.

OK, we’ve counted. Basically, five.

Apart from minor players like ascorbic and oxalic, there are three main acids in fruits. Citric comes from citrus fruits, needless to say. Usually it’s administered as a squeeze of lemon juice, but in some parts of Central Europe and the Middle East, cooks use granulated citric acid, known as sour salt or lemon salt (in Turkish, limon tuzu).

Most fruits get a gentler sour flavor from malic acid. (Grapes, however, contain an equal amount of tartaric acid, which is also found in tamarind and, hence, in Worcestershire sauce.) Middle Eastern cooks regularly flavor dishes with sour fruit juices: sour grape juice (verjus), which is sold in Iranian markets as a^b-e ghureh, and sour pomegranate syrup (dibs rumma^n, rob-e ana^r).

Two other sour flavors come from microbial action. Lactic acid is found in fermented dairy products such as buttermilk, yogurt and cheese, and in sourdough bread, sauerkraut and dill pickles. Kvass, a sort of mild, yeasty beer made from black bread, is sometimes used in Russian cooking for its sour flavor, mostly due to lactic acid. At least one Swiss company bottles diluted lactic acid as a sort of “yogurt vinegar” (it looks like whey that’s been sitting around for a while).

The best-known bacterial acid is acetic. It’s the acid of vinegar--and of most things that have spoiled, in fact, so it’s the most widespread sour ingredient in the world. It’s volatile, making it the only food acid that you can actually smell. In some countries it’s sold as concentrated acetic acid, to be diluted with a lot of water before going on your salad. It’s so strong that in the former Soviet Union this sort of super-vinegar was often used for committing suicide.