Yogurt

History

Genome sequencing of Lactobacillus delbrueckii subsp. bulgaricus shows that the lactic acid bacteria adapted from a plant-associated habitat into the lactose-rich and stable protein milk environment through the loss of superfluous functions and protocooperation with Streptococcus thermophilus. The two bacteria used for modern yogurt production may have originated from plants in Bulgaria, where viable, fermenting strains of L. d. bulgaricus and S. thermophilus have been cultivated from plant samples.

Yogurt containing L. d. bulgaricus and S. thermophilus was first identified by the Bulgarian physician and microbiologist Stamen Grigorov in 1905. Grigorov experimented with samples of home-made Bulgarian yogurt or soured milk which he had brought from his native village, notably describing Bacille A., later named Bacillus bulgaricus and now known as Lactobacillus delbrueckii subsp. bulgaricus, as a small rod-shaped bacterium that caused milk to curdle and turn into yoghurt. The preparation of fermented milk products in the Balkan Peninsula existed by the 7th century AD, where a form of yogurt called katuk was prepared by the Bulgars, a historical Turkic tribe.

The origins of yogurt are unknown but it was probably discovered first by Neolithic people in Central Asia and Mesopotamia around 5000 BC, when the first milk-producing animals were domesticated. They most likely found out how to ferment milk by chance and in all likelihood, yogurt was discovered independently in this way in many different places at different times.

The cuisine of ancient Greece included a dairy product known as oxygala (ὀξύγαλα) which was a form of yogurt. Galen (AD 129 – c. 200/c. 216) mentioned that oxygala was consumed with honey, similar to the way thickened Greek yogurt is eaten today. The oldest writings mentioning yogurt are attributed to Pliny the Elder, who remarked that certain "barbarous nations" knew how "to thicken the milk into a substance with an agreeable acidity". The use of yogurt by medieval Turks is recorded in the books Dīwān Lughāt al-Turk by Mahmud Kashgari and Kutadgu Bilig by Yusuf Has Hajib written in the 11th century. Both texts mention the word "yogurt" in different sections and describe its use by nomadic Turks. The earliest yogurts were probably spontaneously fermented by wild bacteria in goat skin bags.

Until the 1900s, yogurt was a staple in diets of people in the Russian Empire (and especially Central Asia and the Caucasus), Western Asia, South Eastern Europe/Balkans, Central Europe, and the Indian subcontinent. Stamen Grigorov (1878–1945), a Bulgarian student of medicine in Geneva, first examined the microflora of the Bulgarian yogurt. In 1905, he described it as consisting of a spherical and a rod-like lactic acid-producing bacteria. In 1907, the rod-like bacterium was called Bacillus bulgaricus (now Lactobacillus delbrueckii subsp. bulgaricus). The Russian biologist and Nobel laureate Ilya Mechnikov, from the Institut Pasteur in Paris, was influenced by Grigorov's work and hypothesized that regular consumption of yogurt was responsible for the unusually long lifespans of Bulgarian peasants. Believing Lactobacillus to be essential for good health, Mechnikov worked to popularize yogurt as a foodstuff throughout Europe.

Industrialization of yogurt production is credited to Isaac Carasso, who, in 1919, started a small yogurt business in Barcelona, Spain, naming the business Danone ("little Daniel") after his son. The brand later expanded to the United States under an Americanized version of the name, Dannon. Yogurt with added fruit jam was patented in 1933 by the Radlická Mlékárna dairy in Prague.

Yogurt was introduced to the United States in the first decade of the twentieth century, influenced by Élie Metchnikoff's The Prolongation of Life; Optimistic Studies (1908); it was available in tablet form for those with digestive intolerance and for home culturing. It was popularized by John Harvey Kellogg at the Battle Creek Sanitarium, where it was used both orally and in enemas, and later by Armenian immigrants Sarkis and Rose Colombosian, who started the Colombo and Sons Creamery in Andover, Massachusetts, in 1929.

Colombo yogurt was reportedly first delivered around New England in a horse-drawn wagon bearing the Armenian word "madzoon"; this was later replaced with "yogurt", a term that was more familiar to many of the company's customers from the eastern Mediterranean and Near East. Yogurt's popularity in the United States was enhanced in the 1950s and 1960s, when it was presented as a health food by scientists like Hungarian-born bacteriologist Stephen A. Gaymont. Plain yogurt still proved too sour for the American palate and in 1966 Colombo Yogurt sweetened the yogurt and added fruit preserves, creating "fruit on the bottom" style yogurt. This was successful and company sales soon exceeded $1 million per year. By the late 20th century, yogurt had become a common American food item and Colombo Yogurt was sold in 1993 to General Mills, which discontinued the brand in 2010.

Nutrition

Plain yogurt from whole milk is 81% water, 9% protein, 5% fat, and 4% carbohydrates, including 4% sugars. A 100-gram amount provides 406 kilojoules (97 kcal) of dietary energy. As a proportion of the Daily Value (DV), a serving of yogurt is a rich source of vitamin B₁₂ (31% DV) and riboflavin (23% DV), with moderate content of protein, phosphorus, and selenium (14 to 19% DV; table).

Tilde (~) represents missing or incomplete data. There is little difference between whole milk and yogurt made from whole milk with respect to the listed nutritional constituents.

Health research

Because it may contain live cultures, yogurt is often associated with probiotics, which have been postulated as having positive effects on immune, cardiovascular or metabolic health.

A 2011 review stated that high-quality clinical evidence was insufficient to conclude that consuming yogurt lowers the risk of diseases or otherwise improves health. Meta-analyses found that consuming 80 grams per day of low-fat yogurt was associated with a lower risk of developing type 2 diabetes and a lower incidence of hip fracture in post-menopausal women. A 2021 review found a cause-and-effect relationship between yogurt consumption and improved lactose tolerance and digestion, and that potential associations exist between yogurt consumption and improving bone health, as well as lowering the risk of some diseases, including cancers and metabolic syndrome. Daily intake of 50 grams of yogurt has been shown to reduce risk of overweight or obesity by 13%, and reduce risk of type 2 diabetes by 7%. Yogurt consumption has been associated with reduced risk of cardiovascular disease, and insulin resistance. Some of the benefits were somewhat better for the lower fat yogurts. Many commercial yogurt products are supplemented with extra probiotic bacteria.

Safety

Yogurt made with raw milk can be contaminated with bacteria that can cause significant illness and even result in death, including Listeria, Cryptosporidium, Campylobacter, Brucella, Escherichia coli and Salmonella. Yogurts can also be contaminated with aflatoxin-producing Aspergillus flavus, Aspergillus parasiticus and Aspergillus nomius.

Contamination occurs in traditionally prepared yogurts more often than industrially processed ones, but may affect the latter as well if manufacturing and packaging practices are suboptimal.

When mold forms on yogurt, scraping it off does not eliminate it, as yogurt's consistency allows the mold to penetrate and spread deeply under the surface.

Varieties and presentation

Various techniques for fermenting milk into yogurts exist across countries and local regions.

Dahi is a yogurt from the Indian subcontinent, known for its characteristic taste and consistency. The word dahi seems to be derived from the Sanskrit word dadhi ("sour milk"), one of the five elixirs, or panchamrita, often used in Hindu ritual. Sweetened dahi (mishti doi or meethi dahi) is common in eastern parts of India, made by fermenting sweetened milk. While cow's milk is currently the primary ingredient for yogurt, goat and buffalo milk were widely used in the past, and valued for the fat content (see buffalo curd).

Bogurar doi is a traditional sweetened yogurt originating from Bogura, Bangladesh. It is a widely-consumed regional dairy product, forming part of Bangladeshi culinary heritage. It has formal recognition as a geographical indication product in Bangladesh.

Dadiah or dadih is a traditional West Sumatran yogurt made from water buffalo milk, fermented in bamboo tubes. Yogurt is common in Nepal, where it is served as both an appetizer and dessert. Locally called dahi, it is a part of the Nepali culture, used in local festivals, marriage ceremonies, parties, religious occasions, family gatherings, and so on. One Nepalese yogurt is called juju dhau, originating from the city of Bhaktapur. In Tibet, yak milk (technically dri milk, as the word yak refers to the male animal) is made into yogurt (and butter and cheese) and consumed.

In Northern Iran, mâst chekide is a variety of kefir yogurt with a distinct sour taste. It is usually mixed with a pesto-like water and fresh herb purée called delal. Common appetizers are spinach or eggplant borani, and wild shallots.

Matzoon is an Armenian yogurt in the Caucasus and Russia. Tarator and cacık are cold soups made from yogurt in eastern Europe. They are made with ayran, cucumbers, dill, salt, olive oil, and optionally garlic and ground walnuts. Tzatziki in Greece and milk salad in Bulgaria are thick yogurt-based salads similar to tarator.

Khyar w laban (cucumber and yogurt salad) is a dish in Lebanon and Syria. Also, a wide variety of local Lebanese and Syrian dishes are cooked with yogurt like "kibbi bi laban" rahmjoghurt, a creamy yogurt with much higher fat content (10%) than many yogurts offered in English-speaking countries. Dovga, a yogurt soup cooked with a variety of herbs and rice, is served warm in winter or refreshingly cold in summer. Jameed, yogurt salted and dried to preserve it, is consumed in Jordan. Zabadi is the type of yogurt made in Egypt, usually from the milk of the Egyptian water buffalo. It is particularly associated with Ramadan fasting, as it is thought to prevent thirst during all-day fasting.

Sweetened and flavored

To offset its natural sourness, yogurt is also sold sweetened, sweetened and flavored or in containers with fruit or fruit jam on the bottom. The two styles of yogurt commonly found in the grocery store are set-style yogurt and Swiss-style yogurt. Set-style yogurt is poured into individual containers to set, while Swiss-style yogurt is stirred prior to packaging. Either may have fruit added to increase sweetness.

Lassi is a common Indian beverage made from stirred liquified yogurt that is either salted or sweetened with sugar commonly, less commonly honey and combined with fruit pulp to create flavored lassi. Consistency can vary widely, with urban and commercial lassis having uniform texture through being processed, whereas rural and rustic lassi has discernible curds or fruit pulp.

Large amounts of sugar – or other sweeteners for low-energy yogurts – are often used in commercial yogurt. Some yogurts contain added modified starch, pectin (found naturally in fruit) or gelatin to create thickness and creaminess. This type of yogurt may be marketed under the name Swiss-style, although it is unrelated to conventional Swiss yogurt. Some yogurts, often called "cream line", are made with whole milk which has not been homogenized so the cream rises to the top. In many countries, sweetened, flavored yogurt is common, typically sold in single-serving plastic cups. Common flavors may include vanilla, honey, and toffee, and various fruits. In the early 21st century, yogurt flavors inspired by desserts, such as chocolate or cheesecake, became common. There is concern about the health effects of sweetened yogurt due to its high sugar content, although research indicates that use of sugar in yogurt manufacturing has decreased since 2016 in response to WHO and government initiatives to combat obesity.

Straining

Strained yogurt has been strained through a filter, traditionally made of muslin and more recently of paper or non-muslin cloth. This removes the whey, giving a much thicker consistency. Strained yogurt is made at home, especially if using skimmed milk which results in a thinner consistency. Yogurt that has been strained to filter or remove the whey is known as labneh in Middle Eastern countries. It has a consistency between that of yogurt and cheese. It may be used for sandwiches in Middle Eastern countries. Olive oil, cucumber slices, olives, and various green herbs may be added. It can be thickened further and rolled into balls, preserved in olive oil, and fermented for a few more weeks. It is sometimes used with onions, meat, and nuts as a stuffing for a variety of pies or kibbeh balls.

Some types of strained yogurts are boiled in open vats first, so that the liquid content is reduced. The East Indian dessert, a variation of traditional dahi called mishti dahi, offers a thicker, more custard-like consistency, and is usually sweeter than western yogurts. In western Indian (Marathi and Gujarati) cuisine, strained yogurt is macerated with sugar and spices such as saffron, cardamom and nutmeg to make the dessert "shrikhand". Strained yogurt is also enjoyed in Greece and is the main component of tzatziki, a well-known accompaniment to gyros and souvlaki pita sandwiches: it is a yogurt sauce or dip made with the addition of grated cucumber, olive oil, salt and, optionally, mashed garlic. Srikhand, a dessert in India, is made from strained yogurt, saffron, cardamom, nutmeg and sugar and sometimes fruits such as mango or pineapple.

In North America, strained yogurt is commonly called "Greek yogurt". Powdered milk is sometimes added in lieu of straining to achieve thickness. In Britain and the European Union, "Greek" is considered a designation of origin and may only be applied to yogurt made in Greece.

Beverages

Ayran, doogh (Persian: دوغ; Assyrian Neo-Aramaic: dawghe) or dhallë (Albanian, lit. 'buttermilk') is a yogurt-based beverage in Middle Eastern cuisine made by mixing yogurt with water and sometimes salt.

Borhani (or burhani) is a spicy yogurt drink from Bangladesh. It is usually served with kacchi biryani at weddings and special feasts. Key ingredients are yogurt blended with mint leaves (mentha), mustard seeds and black rock salt (Kala Namak). Ground roasted cumin, ground white pepper, green chili pepper paste and sugar are often added.

Lassi is a yogurt-based beverage in South Asian cuisine that may be salty or sweet, and may be flavored with rosewater, mango or other fruit juice. Salty lassi is usually flavored with ground, roasted cumin and red chilies, and may be made with buttermilk.

An unsweetened and unsalted yogurt drink usually called simply jogurt is consumed with burek and other baked goods in the Balkans. Sweetened yogurt drinks are the usual form in Europe (including the UK) and the US, containing fruit and added sweeteners. These are typically called "drinkable yogurt". Also available are "yogurt smoothies", which contain a higher proportion of fruit and are more like smoothies.

Production

Yogurt is made by warming milk to a temperature (30–45 °C (86–113 °F)) that will not kill the live microorganisms that turn the milk into yogurt, inoculating certain bacteria (starter culture), usually Streptococcus thermophilus and Lactobacillus bulgaricus, into the milk, and then keeping it warm for several hours (4–12 hours).

Milk with added dried milk produces a firmer yogurt. Yogurt production provides two significant barriers to pathogen growth, heat and acidity (low pH). Both are necessary to ensure a safe product. Acidity alone is insufficient, as shown by recent outbreaks of food poisoning by E. coli O157:H7 that is acid-tolerant. E. coli O157:H7 is easily destroyed by pasteurization (heating); the initial heating of the milk kills pathogens as well as denaturing proteins. The microorganisms that turn milk into yogurt can tolerate higher temperatures than most pathogens, so that a suitable temperature not only encourages the formation of yogurt, but inhibits pathogenic microorganisms. Once the yogurt has formed it can, if desired, be strained to reduce the whey content and thicken it.

Microstructure

Yogurt is a viscous, shear-thinning, non-Newtonian fluid that forms when milk, a Newtonian fluid, is fermented, causing protein aggregation and subsequent gelation. The result is a soft solid that can be modeled via the interactions of the casein proteins. The microstructure of yogurt is affected by its fat and protein content and its processing conditions. In low-fat formulations, the microstructure is a network of casein protein globules joined via clusters and strands that encapsulate pores: these pores house the aqueous phase and the bacterial cultures of the yogurt.

Stirred yogurt formulations have a coarser distribution of loosely associated casein particulates due to the shear forces and resulting particle-particle collisions induced during the mixing process. After stirring, yogurt is more accurately defined as a weak gel.

Rheology

The mechanical properties of yogurt are typically assessed using rheometry, which quantifies the deformation and flow response of soft materials subject to shear forces. As is central in materials science, the rheological properties of yogurt are dictated by a variety of processing factors, including the ratios of dry and wet matter, thermal treatments, milk origin, starter cultures, and yogurt type.

Although cow milk is a common choice for yogurt production, other milks, such as goat, sheep, and camel, produce different rheologies. Goat milk yogurt has a low viscosity and a thinner texture when compared to cow milk yogurt. Conversely, sheep milk, having higher content of solids, has a higher viscosity and thicker texture when compared to cow milk yogurt.

Yogurt can further be characterized as "set" versus stirred, wherein set yogurts are processed and sold in the same container, and stirred yogurts are mixed prior to packaging in a secondary container.

Commerce

Two types of yogurt are supported by the Codex Alimentarius for import and export.

• Pasteurized yogurt ("heat treated fermented milk") is yogurt pasteurized to kill bacteria.
• Probiotic yogurt (labeled as "live yogurt" or "active yogurt") is yogurt pasteurized to kill bacteria, with Lactobacillus added in measured units before packaging.
• Yogurt probiotic drink is a drinkable yogurt pasteurized to kill bacteria, with Lactobacillus added before packaging.

Under US Food and Drug Administration regulations, milk must be pasteurized before it is cultured, and may optionally be heat treated after culturing to increase shelf life. Most commercial yogurts in the United States are not heat treated after culturing, and contain live cultures.

Yogurt with live cultures is more beneficial than pasteurized yogurt for people with lactose malabsorption.

Lactose intolerance

Lactose intolerance is a condition in which people have symptoms due to the decreased ability to digest lactose, a sugar found in dairy products. In 2010, the European Food Safety Authority (EFSA) determined that lactose intolerance can be alleviated by ingesting live yogurt cultures (lactobacilli) that are able to digest the lactose in other dairy products. The scientific review by EFSA enabled yogurt manufacturers to use a health claim on product labels, provided that the "yogurt should contain at least 10⁸ CFU live starter microorganisms (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus) per gram. The target population is individuals with lactose maldigestion". A 2021 review found that yogurt consumption could improve lactose tolerance and digestion.

Plant-based products

A variety of plant-based yogurt alternatives appeared in the 2000s, using soy milk, rice milk, and nut milks such as almond milk and coconut milk fermented with cultures. These products may be suitable for people with lactose intolerance and those who prefer plant-based foods, such as vegetarians and vegans. Plant-based milks have different structures and components than dairy milk. Though they can be used to make many products similar to those made from dairy, there are differences in taste and texture, and some consumers may feel that they lack the "delicate and smooth structure" of "conventional yogurts". Since plant-based milks do not contain lactose (the food of Streptococcus thermophilus and Lactobacillus bulgaricus), plant-based products usually contain different bacterial strains than yogurt, such as Lactobacillus casei, Lactobacillus rhamnosus, and Bifidobacterium bifidum. Plant-based products also vary considerably in their nutrition and ingredients and may contain gums, stabilizers, high-intensity sweeteners, and artificial colors.

In Europe, companies may not market their plant-based products using the word yogurt since that term is reserved for products of animal origin only – per European Union regulation 1308/2013 and a 2017 ruling in the Court of Justice of the European Union. Reaffirmed in 2021, per the US FDA's Standard of Identity regulations, the word yogurt has been reserved for a product made from lactation and is a product of "milk-derived ingredients".

Ant yogurt

Red wood ants have been used in Bulgaria and Turkey to make yogurt; a few ants are added to warm milk and left to ferment. Modern studies suggest that the ants' formic acid acidulates the milk, enabling microbes from the ants' microbiomes to thrive, and ant or bacterial enzymes break down milk proteins to produce a yogurt.