yogurt

also yo·ghurt or yo·ghourt (yō'gərt)
n.
A custardlike food with a tart flavor, prepared from milk curdled by bacteria, especially Lactobacillus bulgaricus and Streptococcus thermophilus, and often sweetened or flavored with fruit.

[Turkish yoğart, yoğurt, from yoğur, to knead.]

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is the preferred spelling, although yoghurt (with an h) is also common. It is pronounced yog-ǝt in British English, and yoh-gǝt in American English and in Australia and New Zealand.

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Milk fermented by lactic fermentation process. Yogurt is thought to be originally from Bulgaria. It is made from cow, goat, sheep and soy milk to which bacteria are added that convert part of the lactose (the main sugar in milk) into lactic acid: Lactobacillus bulgaricus and Streptococcus thermophilus. The milk coagulates when enough lactic acid is produced. When the yogurt has fermented enough, it needs to be cooled. Whether it is plain, stirred or set, the basic yogurt mixture essentially remains the same. Commercial manufacturing processes result in a firmer yogurt that is less likely to release whey, the yellowish liquid sometimes found on the surface of natural yogurts. There is a wide range of yogurts, including set yogurt (the oldest kind), stirred yogurt (a Swiss-invented process) and various products such as frozen yogurt, drinking yogurt and dehydrated yogurt.

Plain yogurt is made with either whole, lowfat or nonfat milk. It contains no additional flavorings or ingredients.

Set yogurt has the appearance of a compact jelly. It is fermented in a container, then cooled; if it is flavored with natural or artificial products, they are generally found at the bottom of the container. 

Stirred yogurt is mixed following the fermentation and cooling process, which makes the product smooth and even. It can be flavored with natural or artificial ingredients, such as fruit.

Drinking yogurt is made from fermented milk, to which a fruit-flavored syrup or sugar and fruit has been added, and is sometimes promoted as an alternative to carbonated soft drinks.

Frozen yogurt is similar to soft-serve ice cream in texture.

Several of these products have been pasteurized or treated using the ultra-high temperature (UHT) process, and may contain additives.

There are also other forms of fermented milk.

Curdled milk is milk that has been fermented at room temperature using just the action of the lactic flora present in the milk. Curdled milk separates into two distinct parts: the curds and the whey. It is consumed as is after being stirred or drained. It must be used as soon as possible and stored in the fridge.

Kefir, or "kephir," probably originally from the Caucasus, is whole or reduced-fat milk that is fermented using several species of bacteria and yeasts, making it slightly fizzy and alcoholic, with a sharp and somewhat bitter flavor. The alcohol level is generally 1%. Kefir can be liquid, creamy and alcoholic depending on the length of the fermentation period. It froths and bubbles in a way that is similar to beer. It can be made with dried fruits or lemon. Kefir keeps in the fridge and is more perishable than yogurt. It can still be used after it sours, especially for cooking. It is delicious served chilled and garnished with mint leaves, or poured over fruit. It can be a beverage, used or eaten in the same way as yogurt.

Kumis is similar to kefir, but it is more alcoholic, with up to 2.5% alcohol. It is made with mare, donkey or cow's milk and is traditionally popular in Central Asia. Its flavor is reminiscent of white wine.

Buying

Check the use-by or sell-by date when buying. After the indicated date, the yogurt may still be edible as long as it has a good taste and no molds or bubbles have appeared. The formation of liquid is not a sign of spoiling.

Preparing

Making yogurt at home is easy and economical, and provides yogurt without any added sugar and containing vitamins A and D.

Utensils must be carefully washed and rinsed well in hot water or sterilized before using.

Milk is heated to 185°F (85°C) for about 30 min, after adding 3%-5% powdered skim milk. The fresh milk used at the start can be whole, reduced-fat or even UHT milk.

The level of fat and milk solids in the milk 
will affect the texture, flavor and nutritional value of the yogurt. Whole milk results in a firmer, tastier yogurt that is higher in fat and energy than a yogurt made from skim milk. The addition of milk powder (3-8 tablespoons/45-120 ml per 4 cups/1 l of milk) thickens the yogurt, makes it creamier and increases its nutritional value.

Gelatin or pectin can be added to the milk when it reaches the boiling point, if desired; measure 1 teaspoon (5 ml) per 4 cups (1 l) of milk. Let it swell up completely in a small amount of milk before mixing it in (gelatin is not required if a dehydrated culture is used, as the resulting yogurt is firm).

The use of a thermometer helps to monitor the boiling and establishes the exact moment to add the ferment.

Cool the milk to 110°F-115°F (43°C-46°C), then culture the yogurt with a ferment or a dehydrated (freeze-dried) culture, plain commercial yogurt (2-5 tablespoons/30-75 ml per 4 cups/1 l of milk) that still contains live bacteria (but not starch or gelatin) and is as fresh as possible, or homemade yogurt prepared within the previous 5 days.

In order to minimize contamination risks, take care (before eating the yogurt) to set aside the amount needed for the next culture. 

Yogurt made with a dehydrated culture is creamier, thicker and less acidic than a yogurt made with a commercial yogurt; moreover, it keeps these qualities for a longer time and it can be used more than once to make more yogurt. After about 1 month, or 3 batches, the yogurt degenerates and a new ferment must then be used.

Avoid stirring yogurt while it is setting, or it will separate and become watery. Leave it to incubate for 4-6 hr at a constant temperature of at least 105°F (40°C).

The incubation temperature of yogurt is crucial. The ideal temperature is 105°F-115°F (40°C-46°C); don't allow the temperature to go above 115°F (46°C), or the heat will destroy the bacteria and prevent it setting; it is slower under 105°F (40°C), when a lower temperature prolongs the setting time and makes the yogurt more sour.

The use of a yogurt-maker is practical but not essential. Any source of constant heat protected from drafts will fulfill the same function. Yogurt can be incubated in an oven preheated to 120°F (50°C) or an oven with a bulb that provides the necessary heat. One can also use an insulated bottle (thermos) that has been heated beforehand, a plate or frying pan filled with hot water and covered with a thick cloth to keep the heat in, or a container wrapped in a blanket and placed in a turned-off oven, on a heater or near a weak but constant heat source.

When the yogurt has set, or when the desired texture and taste have been reached, refrigerate immediately to stop the activity. Fruits or other ingredients are added just before eating.

If the yogurt does not thicken, there may be more than one factor responsible: the culture may be too old, the temperature may be too high or too low, the incubation time may not be long enough or the amount of dry extracts (milk powder) too low. Reintroduce a ferment, add some milk powder, if desired, and incubate again. 

If the yogurt is sour or the whey separates, the incubation may have been too long or the cooling process too slow. Mix the whey back into the yogurt by beating it (the mixture will, however, be more watery).

Homemade yogurt can be kept for 3 weeks in the fridge.

Serving Ideas

Yogurt is eaten as is and can also be cooked. It is added to soups, salads, meat, poultry, fish, rice, pasta dishes, breads, cakes, pies, brioches, desserts and drinks. Yogurt is used as a basic ingredient in several hot or cold soups, as well as for making cold sauces for grilled skewers. It is used to marinate 
and tenderize meat, poultry and game.

It is an important ingredient in Middle Eastern and Indian cuisines (it is an accompaniment to curries and the basis of raitas—fruits or vegetables mixed with flavored yogurt). 

Plain yogurt can be used in place of cream, whether liquid, whipped or sour, and it can be added to mayonnaise or vinaigrette, reducing the level of calories and fat. If using it in place of cream in dishes requiring cooking, yogurt needs to be stabilized by adding a little cornstarch. Bring it to room temperature for 1-2 hr before adding it to hot dishes and, if possible, add at the very end of cooking.

Storing

Avoid keeping at room temperature as much as possible.

At room temperature: dehydrated yogurt ferments, 6 months.

In the fridge: 2-3 weeks; dehydrated ferments, 12 months.

In the freezer: 1 month; dehydrated ferments, 18 months.

Preferably defrost yogurt in the fridge.

Nutritional Information
Excellent source: protein, calcium, phosphorus, potassium and vitamins A and B. 
The nutritional value of plain unsweetened yogurt is almost equivalent to milk with, along with the assumed benefits resulting from the fermentation process. The level of fat, carbohydrates and calories in commercial yogurts varies. Some yogurts contain up to 10% fat. The cholesterol level varies between 7.5 and 12.5 mg for 100 g (3.5 oz) for plain and flavored versions. Its carbohydrate level is generally 7% for plain yogurt and 11%-18% for fruit yogurts. Some yogurts can contain food additives. 

Properties: yogurt is said to favor longevity, be beneficial for the digestive system, useful in treating vaginal inflammations and warding off cancer and, taken before bedtime, encouraging sleep. 

Yogurt is more easily digested than milk and contains bacteria that facilitate the digestion of lactose.

Preparing


Browse other dairy products: Introduction | Milk | Goat's milk | Buttermilk | Sour cream | Butter | Cream | Yogurt | Ice cream | Cheese

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For more information on yogurt, visit Britannica.com.

Background

Yogurt is a dairy product, which is made by blending fermented milk with various ingredients that provide flavor and color. Although accidentally invented thousands of years ago, yogurt has only recently gained popularity in the United States.

It is believed that yogurt originated in Mesopotamia thousands of years ago. Evidence has shown that these people had domesticated goats and sheep around 5000 B.C. The milk from these animals was stored in gourds, and in the warm climate it naturally formed a curd. This curd was an early form of yogurt. Eventually, a process for purposely producing yogurt was developed.

While yogurt has been around for many years, it is only recently (within the last 30-40 years) that it has become popular. This is due to many factors including the introduction of fruit and other flavorings into yogurt, the convenience of it as a ready-made break-fast food and the image of yogurt as a low fat healthy food.

Manufacturers have responded to the growth in the yogurt market by introducing many different types of yogurt including low fat and no-fat, creamy, drinking, bio-yogurt, organic, baby, and frozen. Traditional yogurt is thick and creamy. It is sold plain and in a wide assortment of flavors. These are typically fruit flavors such as strawberry or blue-berry however, newer, more unique flavors such as cream pie and chocolate have also been introduced. Cereals and nuts are some-times added to yogurts. Yogurt makers also sell products with a varying level of fat. Low fat yogurt, which contains between 0.5% and 4% fat, is currently the best selling. Diet no-fat yogurt contains no fat at all. It also contains artificial sweeteners that provide sweetness while still reducing calories. Creamy yogurt is extra thick, made with whole milk and added cream. Drinking yogurt is a thinner product, which has a lower solids level than typical yogurt. Bio-yogurt is made with a different type of fermentation culture and is said to aid digestion. Yogurt that is made with milk from specially fed cows is called organic yogurt. This type of yogurt is claimed to be more nutritious than other yogurts. Other types of yogurts include pasteurized stirred yogurt that has extended shelf life, baby yogurt made specifically for children, and frozen yogurt.

The yogurt itself has a generally aldehydic flavor, which is a result of the fermentation process. Since it is made from milk, yogurt is rich in nutrients. It contains protein and vitamins and is a rich source of calcium. In fact, a small container of yogurt contains as much calcium as a third of a pint of milk. In addition to these nutritional characteristics, yogurt is also thought to have additional health benefits. One of the suggested benefits of yogurt is that it acts as a digestive aid. In the body, it is thought that yogurt can encourage the growth of beneficial bacteria in the gut. These organisms help to digest food more efficiently and protect against other, harmful organisms. Another health benefit of yogurt is for people that are lactose intolerant. These people have difficulty digesting milk products however, they typically can tolerate yogurt.

Raw Materials

In general, yogurt is made with a variety of ingredients including milk, sugars, stabilizers, fruits and flavors, and a bacterial culture (Lactobacillus bulgaricus). During fermentation, these organisms interact with the milk and convert it into a curd. They also change the flavor of the milk giving it the characteristic yogurt flavor of which acetaldehyde is one of the important contributors. The primary byproduct of the fermentation process is lactic acid. The acid level is used to determine when the yogurt fermentation is completed which is usually three to four hours. The suppliers of these yogurt cultures offer various combinations of the two bacterial types to produce yogurts with different flavors and textures.

To modify certain properties of the yogurt, various ingredients may be added. To make yogurt sweeter, sucrose (sugar) may be added at approximately 7%. For reduced calorie yogurts, artificial sweeteners such as aspartame or saccharin are used. Cream may be added to provide a smoother texture. The consistency and shelf stability of the yogurt can be improved by the inclusion of stabilizers such as food starch, gelatin, locust-bean gum, guar gum and pectin. These materials are used because they do not have a significant impact on the final flavor. The use of stabilizers is not required however, and some marketers choose not to use them in order to retain a more natural image for their yogurt.

To improve taste and provide a variety of flavors, many kinds of fruits are added to yogurt. Popular fruits include strawberries, blueberries, bananas, and peaches, but almost any fruit can be added. Beyond fruits, other flavorings are also added. These can include such things as vanilla, chocolate, coffee, and even mint. Recently, manufacturers have become quite creative in the types of yogurt they produce using natural and artificial flavorings.

The Manufacturing
Process

The general process of making yogurt includes modifying the composition of and pasteurizing the milk; fermenting at warm temperatures; cooling it; and adding fruit, sugar, and other materials.

Modifying milk composition

• When the milk arrives at the plant, its composition is modified before it is used to make yogurt. This standardization process typically involves reducing the fat content and increasing the total solids. The fat content is reduced by using a standardizing clarifier and a separator (a device that relies upon centrifugation to separate fat from milk). From the clarifier, the milk is placed in a storage tank and tested for fat and solids content. For yogurt manufacture, the solids content of the milk is increased to 16% with 1-5% being fat and 11-14% being solids-not-fat (SNF). This is accomplished either by evaporating off some of the water, or adding concentrated milk or milk powder. Increasing the solids content improves the nutritional value of the yogurt, makes it easier to produce a firmer yogurt and improves the stability of the yogurt by reducing the tendency for it to separate on storage.

Pasteurization and homogenization

• After the solids composition is adjusted, stabilizers are added and the milk is pasteurized. This step has many benefits. First, it will destroy all the microorganisms in the milk that may interfere with the controlled fermentation process. Second, it will denature the whey proteins in the milk which will give the final yogurt product better body and texture. Third, it will not greatly alter the flavor of the milk. Finally, it helps release the compounds in milk that will stimulate the growth of the starter culture. Pasteurization can be a continuous-or batch-process. Both of these processes involve heating the milk to a relatively high temperature and holding it there for a set amount of time. One specific method for batch process pasteurization is to heat a large, stainless steel vat of milk to 185° F (85° C) and hold it there for at least 30 minutes.
• While the milk is being heat treated, it is also homogenized. Homogenization is a process in which the fat globules in milk are broken up into smaller, more consistently dispersed particles. This produces a much smoother and creamier end product. In commercial yogurt making, homogenization has the benefits of giving a uniform product, which will not separate. Homogenization is accomplished using a homogenizer or viscolizer. In this machine, the milk is forced through small openings at a high pressure and fat globules are broken up due to shearing forces.

Fermentation

• When pasteurization and homogenization are complete, the milk is cooled to between 109.4-114.8° F (43-46° C) and the fermentation culture is added in a concentration of about 2%. It is held at this temperature for about three to four hours while the incubation process takes place. During this time, the bacteria metabolizes certain compounds in the milk producing the characteristic yogurt flavor. An important byproduct of this process is lactic acid.
• Depending on the type of yogurt, the incubation process is done either in a large tank of several hundred gallons or in the final individual containers. Stirred yogurt is fermented in bulk and then poured into the final selling containers. Set yogurt, also known as French style, is allowed to ferment right in the container it is sold in. In both instances, the lactic acid level is used to determine when the yogurt is ready. The acid level is found by taking a sample of the product and titrating it with sodium hydroxide. A value of at least 0.9% acidity and a pH of about 4.4 are the current minimum standards for yogurt manufacture in the United States. When the yogurt reaches the desired acid level, it is cooled, modified as necessary and dispensed into containers (if applicable).

Adding other ingredients

• Fruits, flavors, and other additives can be added to the yogurt at various points in manufacturing process. This is typically dependent on the type of yogurt being produced. Flavor in non-fruit yogurts are added to the process milk before being dispensed into cartons. Fruits and flavors can also be added to the containers first, creating a bottom layer. The inoculated milk is then added on top and the carton is sealed and incubated. If the fruit is pasteurized, it can be added as a puree to the bulk yogurt, which is then dispensed into containers. Finally, the fruit can be put into a special package, which is mixed with plain yogurt upon consumption.
• The finished yogurt containers are placed in cardboard cases, stacked on pallets, and delivered to stores via refrigerated trucks.

Quality Control

Milk products such as yogurt are subject to a variety of safety testing. Some of these include tests for microbial quality, degree of pasteurization, and various forms of contaminants. The microbial quality of the incoming milk is determined by using a dye reaction test. This method shows the number of organisms present in the incoming milk. If the microbial count is too high at this point, the milk may not be used for manufacture. Since complete pasteurization inactivates most organisms in milk, the degree of pasteurization is determined by measuring the level of an enzyme in the milk called phosphatase. Governmental regulations require that this test be run to ensure that pasteurization is done properly. Beyond microbial contamination, raw milk is subject to other kinds of contaminants such as antibiotics, pesticides or even radioactivity. These can all be found through safety testing and the milk is treated accordingly.

In addition to safety tests, the final yogurt product is also evaluated to ensure that it meets the specifications set by the manufacturer for characteristics such as pH, rheology, taste, color, and odor. These factors are tested using various laboratory equipment such as pH meters and viscometers and also human panelists.

The Future

The future of yogurt manufacturing will focus on the development of new flavors and longer lasting yogurts. The introduction of new flavors will be driven by consumer desires and new developments by flavor manufacturers. The suppliers of the bacterial cultures are conducting research that hints at the development of uniquely flavored yogurts. By varying the types of organisms in the cultures, yogurt is produced much faster and lasts longer than conventional yogurt.

Additionally, the nutritional aspects of yogurt will be more thoroughly investigated There is some evidence that has shown consumption of yogurt has a beneficial antibiotic effect. It has also been shown to reduce the incidence of lactose intolerance and other gastro-intestinal illnesses. Other purported benefits of yogurt include the reduction of cholesterol, protection against certain cancers, and even boosting the immune system. The research is still not complete on these benefits however, these factors will likely be important in the continued market growth of yogurt.

Where to Learn More

Books

Helferich, W. and D. Westhoff. Yogurt: All About It, 1980.

Hui, Y.H., ed. Dairy Science and Technology Handbook. New York: Wiley VCH, 1992.

Robinson, R.K. "Snack Foods of Dairy Origin." In Snack Food. Edited by Gordon R. Booth. New York: Van Nostrand Reinhold, 1990, pp. 159-182.

Robinson, R.K and A.Y. Tamime. "Recent developments in yoghurt manufacture." In Modern Dairy Technology. Edited by B.J.F. Hudson. London: Elsevier Applied Science Publishers, 1986, pp 1-36.

[Article by: Perry Romanowski]

Milk (from a variety of animals, but usually cows) coagulated and fermented with two types of bacteria, Streptococcus thermophilus and Lactobacillus bulgaricus. May be pasteurized, when most of the bacteria are destroyed, otherwise termed live yoghurt. Bioyoghurts also contain Lactobacillus acidophilus (see acidophilus milk) and Bifidobacterium bifidum (see probiotics). Soft frozen yoghurt, as a low fat alternative to ice cream was first introduced in 1972.

A 150-g portion of low-fat, unsweetened (natural) yoghurt is a rich source of calcium and iodine, a good source of vitamin B₂, a source of protein and vitamin B₁₂; supplies 80 kcal (340 kJ). When sweetened (and usually flavoured), supplies 130 kcal (550 kJ). If made with full-fat milk and sweetened, a portion contains up to 4.5 g of fat, of which half is saturated and supplies 150 kcal (670 kJ). See also milk, fermented.

[YOH-gert] A dairy product that's the result of milk that has fermented and coagulated because it's been invaded by friendly bacteria. This can be accomplished naturally by keeping the milk at about 110°F for several hours. The end result is a creamy-textured yogurt with an astringent, slightly tart taste. Yogurt-making is thought to have been originated by nomadic Balkan tribes thousands of years ago, probably first by accident and then as a means of preserving milk. Today, yogurt is made commercially in carefully controlled environments and the requisite bacteria (usually Lactobacillus bulgaricus and Streptococcus thermophilus) are added to the milk. Though yogurt can be made from the milk of many animals, cow's milk is the most commonly used. There are a variety of commercial yogurts now produced. Plain yogurt is made from whole milk, lowfat or nonfat milk without additional flavoring ingredients. Flavored yogurt has sugar and either artificial flavorings or natural fruit (or both) added. Some flavored yogurts contain gelatin or stabilizers for a thicker texture. Fruit-flavored yogurts can either have the fruit on the bottom (to be mixed in by the consumer) or be already stirred-in which case they're referred to as Swiss-style. Frozen yogurt-which resembles soft-serve ice cream in texture-has become very popular and competes head-to-head in some markets with ice cream. The health benefits of yogurt have long been touted. It is certainly a good source of B vitamins, protein and calcium and is much more digestible than fresh milk. It's also said to keep the intestinal system populated with good bacteria and therefore in healthy condition. These benefits, however, are thought to be lost when yogurt is frozen, which destroys most of the beneficial bacteria. See also soy yogurt.

Description	Quantity	Energy (calories)	Carbs (grams)	Protein (grams)	Cholesterol (milligrams)	Weight (grams)	Fat (grams)	Saturated Fat (grams)
w/ lofat milk, fruit flavor	8 oz	230	43	10	10	227	2	1.6
w/ lofat milk, plain	8 oz	145	16	12	14	227	4	2.3
w/ nonfat milk	8 oz	125	17	13	4	227	0	0.3
w/ whole milk	8 oz	140	11	8	29	227	7	4.8

sign description: The Y hand makes a scooping motion in the palm of the opposite hand.

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n

A slightly acid, semisolid curdled milk preparation made from either whole or skimmed cow’s milk and milk solids by fermentation with organisms from the genus Lactobacillus. It is rich in B-complex vitamins, and is a good source of protein. It provides a medium in the gastrointestinal tract that retards the growth of harmful bacteria and aids in the absorption of minerals. Also spelled yoghurt.

For a list of words related to yogurt, see:

• Dairy Foods

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See words rhyming with "yogurt."

  See crossword solutions for the clue Yog.

Dansk (Danish)
n. - yoghurt

Nederlands (Dutch)
yoghurt (lichtzure melkspijs)

Français (French)
n. - yaourt, yogourt

Deutsch (German)
n. - Joghurt

Ελληνική (Greek)
n. - γιαούρτι

Italiano (Italian)
yogurt

Português (Portuguese)
n. - iogurte (m)

Русский (Russian)
йогурт

Español (Spanish)
n. - yogur

Svenska (Swedish)
n. - yoghurt

中文（简体）(Chinese (Simplified))
酸乳酪

中文（繁體）(Chinese (Traditional))
n. - 酸乳酪, 優酪乳

한국어 (Korean)
n. - 요구르트

日本語 (Japanese)
n. - ヨーグルト

العربيه (Arabic)
‏(الاسم) لبن ( زبادي), لبن رائب أو رايب‏

עברית (Hebrew)
n. - ‮חלב חמצמץ מוצק-למחצה שעבר תהליך תסיסה, יוגורט‬

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