Over Memorial Day weekend of 1934, Tom Carvel, the founder of the Carvel brand and franchise, suffered a flat tire in his ice cream truck in Hartsdale, New York. He pulled into a parking lot and began selling his melting ice cream to vacationers driving by. Within two days he had sold his entire supply of ice cream and concluded that both a fixed location and soft (as opposed to hard) frozen desserts were potentially good business ideas. In 1936, Carvel opened his first store on the original broken down truck site and developed a secret soft serve ice cream formula as well as patented super low temperature ice cream machines.
Dairy Queen also claims to have invented soft serve. In 1938, near Moline, Illinois, J. F. McCullough and his son, Alex, developed their soft serve formula. Their first sales experiment was August 4, 1938, in Kankakee, Illinois at the store of their friend, Sherb Noble. Within two hours of the "all you can eat" trial sale, they had dished out more than 1,600 servings — more than one every 4.5 seconds.
During the late 1940s, future UK Prime Minister Margaret Thatcher worked briefly as a chemist for food manufacturer J. Lyons and Co., at a time when the company had partnered with the United States distributor Mister Softee and was developing a soft-serve recipe that was compatible with the American machines. Thatcher's precise role at Lyons is unclear, but she is reported to have worked on the company's ice cream products, as well as cakes and pies. A common anecdote, probably spread by her political opponents, is that by "inventing" soft serve ice cream, Thatcher "added air, lowered quality and raised profits", used as a metaphor for her policies later as prime minister.
In the 1960s, ice cream machine manufacturers introduced mechanized air pumps into vending machines, providing better aeration.
Soft serve is generally lower in milk-fat (3% to 6%) than ice cream (10% to 18%) and is produced at a temperature of about −4 °C compared to ice cream, which is stored at −15 °C. Soft serve contains air, introduced at the time of freezing. The air content, called overrun, can vary from 0% to 60% of the total volume of finished product. The amount of air alters the taste of the finished product. Product with low quantities of air has a heavy, icy taste and appears more yellow.  Product with higher air content tastes creamier, smoother and lighter and appears whiter. The optimum quantity of air is determined by the other ingredients and individual taste. It is generally accepted that the ideal air content should be between 33% and 45% of volume. More than this and the product loses taste, tends to shrink as it loses air and melts more quickly than that with less air.
All ice cream must be frozen quickly to avoid crystallization. With soft serve, this is accomplished by a special machine at the point of sale. Pre-mixed product (see definitions below) is introduced to the storage chamber of the machine where it is kept at 3 °C. When product is drawn from the draw valve, fresh mix combined with the targeted quantity of air is introduced to the freezing chamber either by gravity or pump. It is then churned and quick frozen and stored until required.
Pre-mix can be obtained in several forms:
- Fresh liquid that requires constant refrigeration until needed. It can be stored for 5 to 7 days before spoiling by bacterial contamination. Quality can be severely compromised by bacterial contamination and handlers must exercise caution to maintain quality.
- A powdered mix. This is a dried version of the liquid mix. It has the advantage of easy distribution and can be stored for long periods of time without spoiling. Water must be added prior to being churned and frozen. The disadvantage is that water quality cannot be guaranteed and some operators can put too much water in to make it go further. It also should be refrigerated to 3 degrees Celsius prior to use, as airborne and waterborne bacteria can infect it immediately and can grow quickly if the product is warm. Residual bacteria in the refrigerated storage compartment can also be activated by warm product being introduced.
- Ultra heat treated mix, a liquid that has been sterilized and packed in sealed, sterile bags. It can last a very long time without refrigeration and can be poured into the soft serve freezer immediately upon opening. However it should be refrigerated to 3 degrees Celsius prior to use for the same reasons outlined above. At the time of opening, quality can be guaranteed and bacterial counts are zero. Where it is available, health authorities consider it the safest form of soft serve mix on the market. It was first developed for commercial use in New Zealand in 1988 in a joint venture between Tatua Foods, a dairy company and Bernie Cook, owner of Blue Boy, a mobile franchise network.
It should be noted that some forms of soft serve are infused with palm oil. Palm oil is a very low cost high fat filler used in many processed foods.
The following locations are used to refer to soft-serve ice cream in various linguistic communities.
- American ice cream, translated to the local language, is the term used in many European countries and in Israel, alongside the mostly incorrect term Italian ice cream.
- Cream ice cream (krémfagylalt) is the term sometimes used in Hungary.
- Creemee: A term popular in New England. Colloquially accepted to have originated in Vermont.
- Mr Whippy is the term used for soft-serve in the UK, or a 99 if a chocolate flake is added, especially when sold from an ice cream van.
- Soft ice cream or soft-serve ice cream are terms used for soft serve in Greater China. (Chinese: 软冰淇淋; pinyin: ruǎn bīngqílín), (Chinese: 軟雪糕; Jyutping: jyun5 syut8 gou1) and Chinese: 霜淇淋) are the Chinese terms used in Mainland China, Hong Kong and Taiwan respectively.
- Softcream (ソフトクリーム sofutokuriimu?) is used to describe an analogous product in Japan, that can be either savory or sweet, with uniquely Asian flavors such as powdered tea, wasabi, sesame, ume or plum, rose, kabocha or Japanese pumpkin, peach, and grape, among others.
- Soft ice Softeis (Germany), softijs (Netherlands and Flanders), softis (Norway)) is the term used for soft-serve in Norway, Germany, Denmark, the Netherlands, Belgium and several other places in Europe.
- Soft ice cream Gelat tou (Andorra, Catalonia)
- Softee or softie is the term used for soft-serve in India and Pakistan.
- Italian ice cream (glace italienne (France), sorvete italiano (Brazil), lody włoskie (Poland)) is the term used in France, Brazil and Poland.
- Soft ice cream (mjukglass) is the term used for soft-serve in Sweden.
- Machine ice cream (helado de maquina (Dominican Republic), inghetata la dozator (Romania), παγωτό μηχανής (Greece)) is the term used for soft-serve in the Dominican Republic, Romania and Greece.
- Semi-frozen (semi-frio) is the term used in Portugal.
- Soft serve is the term used in Australia. Served in a cone with chocolate flake or hundreds and thousands (sprinkles).
- Soft whip is the term used in Ireland. When served in a cone with a chocolate flake it is commonly referred to as a 99.
- Candy (with Spanish pronunciation) is the name used in Argentina. It can be found in nearly all ice cream parlors.
- Merry Cream is the name used in Lebanon.
- Frozen custard, a style of egg and cream based frozen dessert
- Frozen yogurt, the cultured, frozen milk product, may have a naturally tart flavor
- Ice cream van
- Ice milk, a less than 10% milkfat type of frozen dessert
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- The term soft serve dates from before 1959 (New York Times. June 22, 1958. p. F11. Missing or empty
- "Carvel History".
- "About Tom Carvel".
- "The DQ Team".
- "Dairy Queen History".
- Fromson, Daniel. "The Margaret Thatcher Soft-Serve Myth". The New Yorker. Retrieved 2013-04-17.
- Phipps, Claire (2007-11-16). "Was Margaret Thatcher really part of team that invented Mr Whippy? | Politics | guardian.co.uk". Guardian. Retrieved 2013-04-17.
- "Utah Soft Serve Ice Cream Machine Rental". Utah Soft Serve Ice Cream Machine Rental. Retrieved 2015-08-20.