The name "hamburger" comes from the German city of Hamburg, and can refer to a person from Hamburg. In the wider sense, the word was eventually used for other things, including the beef that came from or was popular in Hamburg. Originally, beef cakes were known as hamburger beef (first mentioned in an American cookbook in 1891), and when this puff cake was sandwiched between bread slices, it became the hamburgers sandwich. In the middle of the 20th century both terms were shortened to "hamburger" or simply "burger". The word has gradually become a collective term and is also used for sandwiches with other flesh layers. It is likely that a snack of 'brötchen' (bread roll) filled with minced meat was taken to the states of German immigrants called "hamburgers" after the Hamburger America Line they sailed on.