In 1906, Upton Sinclair published his book "The Jungle" which exposed the lack of sanitation in the meat packing industry. As a result, many Americans developed a fear of eating processed beef. In the 1920s, Billy Ingram, (one of the founders of White Castle), began a public relations campaign to remake the image of the hamburgers sold in restaurants and to help make the burger a favorite food. In his book "Selling them by the Sack White Castle and the Creation of the American Food", David Gerald Hogan credits Billy Ingram and White Castle for making the hamburger the very popular food it is today, and leading the way for McDonald's and other franchises to follow.

The "cheese hamburger," now simply the cheeseburger, is said to have first appeared in 1924, and credited to grill chef Lionel Sternberger of The Rite Spot restaurant in Pasadena, California. This kind of burger is basically the same as a regular hamburger but with a slice of cheese (cheddar, American, Swiss, Pepper jack, or processed) on top of the patty.

The term "burger" has now become generic, and may refer to sandwiches that have ground meat, chicken, fish (or even vegetarian) fillings other than a beef patty, but share the characteristic round bun. By the mid 20th century both terms were commonly shortened to "hamburger" or simply "burger." However, these "burgers" are usually referred to as "chicken burgers", "fish burgers", etc. A "hamburger" today can also be made with finely chopped beef as well as ground beef.

Hamburgers are usually a feature of fast food restaurants. However, the hamburgers prepared in major fast food establishments are mass-produced in factories and frozen for delivery to the site.[3] These hamburgers are thin and of uniform thickness, differing from the traditional American hamburger prepared in homes and conventional restaurants, which is thicker and prepared by hand from ground beef. Generally most American hamburgers are round, but some fast-food chains, such as Wendy's, sell square-cut hamburgers. Hamburgers in fast food restaurants are usually fried, but some firms, such as Burger King use a grilling process. At conventional American restaurants, hamburgers may be ordered "rare", but normally are served well-done for food safety reasons (see below). Fast food restaurants do not offer this option.

The McDonald's fast-food chain sells a sandwich called the Big Mac that is one of the world's top selling hamburgers. Other major fast-food chains – including Burger King (also known as Hungry Jack's in Australia), A&W, Culver's ,Whataburger, Carl's Jr./Hardee's chain, Wendy's (known for their square patties), Jack in the Box, Cook Out, Harvey's, In-N-Out Burger, Five Guys, Fatburger, Burgerville, Back Yard Burgers, Lick's Homeburger, Roy Rogers, and Sonic – also rely heavily on hamburger sales. Fuddruckers and Red Robin are popular hamburger chains that specialize in mid-tier "restaurant-style" variety of hamburgers. The "slider" style of mini hamburger is still popular regionally in the White Castle and Krystal chains.

Some American establishments offer a unique take on the hamburger beyond what is offered in the fast food restaurants. Notable is Father's Office in Santa Monica, California. The patty is composed of dry-aged sirloin mixed with New York Strip ends topped with applewood-smoked bacon compote. It is topped with maytag blue and Gruyère cheeses, caramelized onions, and arugula on a French roll. In lieu of ketchup, Father's Office serves a blue cheese aioli in a ramekin. Dyer's Burgers in Memphis Tennessee is famous for a deep-fried burger. The proprietors claim that they recycle and re-use the same grease used when the restaurant opened in 1912. The casual dining chain Ruby Tuesday claims to have many different varieties of hamburgers on its menu of various shapes, meat compositions, or grades of beef.

Hamburgers are often served as a picnic and party food, cooked outdoors on barbecue grills. Raw hamburger may contain harmful bacteria that can produce food-borne illness such as Escherichia coli O157H7, so caution is needed when handling them. Hamburger patties can be cooked rare, medium rare, medium, medium well, or well done. These terms refer to how thoroughly the meat is cooked, ranging from having a little bit of pink coloring to being dark brown, cooked almost to a crisp. However because of the potential for food-borne illness, it is recommended that hamburgers should be cooked to an internal temperature of 170°F (80°C). If cooked to this temperature, they will be well done. In certain places and restaurants around the world, restaurants add their own sauces.


Ingredients and dietary aspects
A high-quality hamburger is made entirely of ground beef and seasonings. A hamburger that contains no major ingredients besides beef may be referred to as an "all beef hamburger" or "all beef patties" to distinguish them from inexpensive hamburgers made with added flour, texturized vegetable protein or other fillers to decrease their cost. In the 1930s ground liver was sometimes added to the patties. Some cooks prepare their patties with binders, such as eggs or bread crumbs, and seasonings, such as, parsley, onions, soy sauce, Thousand Island dressing, onion soup mix, or Worcestershire sauce.

After cooking the patty and placing it on a bun, other ingredients are placed on top of the patty as toppings. The most popular include ketchup, mustard, iceberg lettuce, mayonnaise, tomatoes, white onions and pickles, though other ingredients, such as sauerkraut and guacamole are not uncommon.

Recent years have seen the increasing popularity of new types of "burgers" in which alternatives to ground beef are used as the primary ingredient. For example, a turkey burger uses ground turkey meat, a chicken burger uses either ground chicken meat or chicken filets. A buffalo burger uses ground meat from a bison and some mix cow and buffalo meat, thus creating a "Beefalo burger" and an ostrich burger is made from ground seasoned ostrich meat. A deer burger uses ground venison from deer. [4]