meat eaten in the poorest districts of the city in the collective mind of the American public. He tried to change those connotations from White Castle's earliest days. At the same time, he became known to some as the Henry Ford of the hamburger, while inventing a restaurant concept he called the "White Castle System", which helped the hamburger achieve fame. Between 1923 and 1931, the "White Castle System" established almost a hundred restaurants in cities throughout the Midwestern United States. In order to raise awareness among White Castle employees, a newsletter entitled "The hot hamburger" was circulated throughout the company, which challenged the employees to improve the sale of the burgers with a simple idea: to be able to prepare burgers rapidly so anyone could purchase and eat them anytime and anywhere. Instead of waiting for half an hour to be served at a traditional restaurant, the White Castle System provided rapid service and a menu centered around the hamburger. At the time, the hamburger was typically served with coffee. Upton Sinclair's The Jungle had already caused public outrage over the safety of processed meat, so by the 1920s, the general public had come to expect a clean and hygienic hamburger. In addition to offering clean and safe food, White Castle offered regularity and standardization, ensuring that each patty was served in the same manner in each restaurant. At the time, this was an entirely novel idea that would revolutionize the sale of food itself with a style that would come to be known as fast food. During its early years, White Castle emphasized providing quality coffee, and collaborated with universities to publish studies on the nutritional quality of their hamburgers. The success of the White Castle chain was rooted largely in the power of propaganda, something that was both an original innovation and necessary to change the public's negative perception of the hamburger. In 1931, it became the first restaurant to advertise in newspapers, using its old "buy 'em by the sack" slogan. White Castle also pioneered the concept of take-out service, and the restaurant is further known for being the first to market square burgers, called "sliders", which were sold for five cents into the 1940s. White Castle was founded in March 1921 in Wichita, Kansas, by Billy Ingram and his business partner, the cook Walter Anderson, and they opened a second restaurant in Kansas City in