Milkshakes were an alcoholic whiskey drink that has been described as a "...sturdy, healthful eggnog type of drink, with eggs, whiskey, etc., served as a tonic as well as a treat".
By 1900, the term milkshake referred to "wholesome drinks made with chocolate, strawberry, or vanilla syrups."
The milkshake made it into the mainstream when in 1922 a Walgreens employee in Chicago, Ivar "Pop" Coulson, took an old-fashioned malted milk (milk, chocolate, and malt) and added two scoops of ice cream, creating a drink which became popular at a surprising rate, soon becoming a high-demand drink for young adults around the country.
By the 1930s, milkshakes were a popular drink at malt shops.
The automation of milkshakes developed in the 1930s, after the invention of freon-cooled refrigerators provided a safe, reliable way of automatically making and dispensing ice cream.
In the late 1930s, several newspaper articles show that the term "frosted" was used to refer to milkshakes made with ice cream.
In the 1950s, a milkshake machine salesman named Ray Kroc bought exclusive rights to a milkshake maker from inventor Earl Prince, and went on to use automated milkshake machines to speed up production in a major fast-food chain.
In 2000 there was developed a reduced-sugar, low-fat milk shakes for school lunch programs. The shakes have half the sugar and only 10% of the fat of commercial fast-food shakes.
In the 2000s, milkshakes began being used as part of the new trend of boutique-style "spa dentistry," which aim to relax dental patients and reduce their anxiety.
Nowadays we are lucky that we can a good milkshake. Just like the smoothie there are a countless number of flavors when it comes to milkshakes.