Schmaltz is rendered fat. In Jewish tradition, it is made by rendering chicken or goose fat, and the term is also used in parts of Germany and Poland to refer to rendered pork fat utilized in traditional cuisine. This rendered fat can be used for frying and flavoring, and as a spread for things like breads. Like other types of refined fat used in traditional cookery, schmaltz arose out of necessity, and became so well integrated into traditional cuisine that it is now a prized ingredient. Traditionalists argue that they can also detect substitutions for the original ingredient in updated dishes.
The fat is rendered by chopping raw fat into small pieces and cooking it slowly to allow it to liquefy. Then, the fat is poured off, leaving solid pieces behind, and it may be filtered for clarity. When it is rendered properly, schmaltz should not go rancid, as the water and proteins which cause this have been removed. The fat will also be creamy to white in color.
Cooks started working with schmaltz because they lacked access to cooking oils such as olive and vegetable oil. Rather than allowing fat from animal sources to go to waste, cooks utilized this fat, eventually refining fat specifically for schmaltz. Some cooks flavor theirs by adding apples and onions in as it renders, creating remains known as gribenes which are packed with flavor. The fat can be used for everything from oiling pans to seasoning noodle dishes, and some people use it as a spread like butter on their bread, with schmaltz tending to go best with dark, hearty breads like traditional rye.
When made from pig fat, schmaltz is of course not kosher, but the resulting lard can be used in many German and Polish dishes. Rendered lard is sometimes available from Mexican and Germany grocery stores, while true schmaltz can be found in stores which cater to European Jewish communities. Cooks can also make their own, with some butchers selling raw fat for home cooks.
The word schmaltz is Yiddish, borrowed directly from the German. Aside from referring to fat, the term is also used to describe excessive or maudlin sentimentality. This use appears primarily in the United States, where a number of Yiddish loanwords are utilized as slang, such as "schmuck," "loafer," and "bluffer." This slang usage of the word is probably related to the intense and overpowering flavor and texture of schmaltz, which can feel excessive to people who are not familiar with this ingredient.