Sauerkraut is a German food: cabbage cut thin, packed with salt, and left until it turns sour. The sour taste is not mainly from pouring vinegar on at the start; the cabbage changes by itself in the salt, and that tang is the point. People eat it with sausages, pork, or on a hot dog. English borrowed the German name and still uses it for this one dish, not for every sour cabbage on earth. Though actually, kitchens nearby do similar things — Taiwan and Dongbei 酸菜, Korean kimchi — but those are different foods with different spices and methods, and English keeps a separate word for the German kind. It can sound a little foreign in English; that is fine. Nobody uses it as a fancy metaphor much, except the odd joke about a sour mood.