Yogurt: Understanding Its Production, Varieties, and Health Implications

Table of Contents

• Introduction
• What is Yogurt?
• History of Yogurt
• Ingredients of Yogurt
• Manufacture of Yogurt
• Microbiology of Yogurt
• Types of Yogurt
• Health Benefits of Yogurt
• Harmful effects of Yogurt

Introduction

• The FDA defines yogurt as a “food produced by culturing one or more of the optional dairy ingredients (cream, milk, partially skimmed milk, and skim milk) with a characterizing bacteria culture that contains the lactic acid-producing bacteria, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus.”
• Milk fermentation is among the oldest preservation methods humans have adopted to extend the shelf life of milk.
• According to the Codex Alimentarius, yogurt is a rich source of protein and other important nutrients.

What is Yogurt?

Yogurt is a fermented milk product created by combining two specific starter bacteria: Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

• In yogurt production, natural milk derivatives such as whey concentrates, skim milk powder, caseinates, or creams are added to form a gel structure due to the coagulation of milk proteins and the presence of lactic acid produced by these specific bacteria, which must be abundant at the time of consumption.
• Besides providing several essential nutrients, yogurt also contains probiotics, fiber, vitamins, and minerals. Sweeteners, fruits, flavors, rice, soy, and nuts can be added to modify its consistency and aroma according to taste.
• Yogurt is highly digestible and bioavailable, making it a healthy food option. It is also recommended for individuals with lactose intolerance, gastrointestinal disorders such as inflammatory bowel disease and irritable bowel disease, and can aid in weight loss and boosting immunity.

History of Yogurt

• Approximately 5,000 years ago, yogurt was known to humans, particularly among the nomadic people of the Middle East.
• Throughout history, various civilizations have consumed yogurt.
• The term "yogurt" originated in the 8th century from the Turkish word “yogurmak,” meaning to thicken, coagulate, or curdle.
• Fermented milk products are mentioned in Indian Ayurvedic scripts dating back to around 6000 BC.
• In 100 BC, the Greeks were the first to reference yogurt in written texts.
• Around 1542, yogurt made its appearance in France, where King Francis I cured himself of chronic diarrhea by consuming it.
• Genghis Khan, the founder of the Mongol Empire, believed yogurt instilled bravery in his soldiers.
• In 1905, Bulgarian medical student Stamen Grigorov, who studied in Geneva, Switzerland, named Bacillus bulgaricus, a lactic acid bacterium found in Bulgarian yogurt.
• In 1909, Russian Nobel laureate Yllia Metchnikoff from the Pasteur Institute in Paris suggested that the lactobacilli in yogurt contributed to the longevity of Bulgarian peasants.
• In 1919, Isaac Carasso began the commercial production of yogurt in Barcelona, Spain, marking another significant event in yogurt’s history.
• Heineman described an early method of making yogurt in 1921.
• The first yogurt laboratory and factory in France opened in 1932, followed by the first in the United States in 1941.
• Flavored yogurts, such as fruit yogurts and yogurts with fruit on the bottom, were introduced in 1937, 1947, and 1963.
• Before the 1960s, yogurt was sold in a few grocery and health food stores.
• In the 1960s, the private company Danone industrialized yogurt production and spread it throughout Europe.
• In 1984, the FAO/WHO defined yogurt as “coagulated milk obtained by lactic acid fermentation by Lactobacillus delbrueckii spp. Lactobacillus bulgaricus (Lb. bulgaricus) and Streptococcus thermophilus from milk."
• Today, yogurt is known by various names around the world, such as Dahi or Dahee in India, Roba in Iraq, Fiili in Finland, Zabadi in Egypt, Mast in Iran, Lebenraib in Saudi Arabia, Laban in Iraq and Lebanon, Roba in Sudan, Iogurte in Brazil, Cuajada in Spain, Coalhada in Portugal, Dovga in Azerbaijan, and Matsoni in Georgia, Russia, and Japan.
• Currently, many forms of yogurt are available, including plain yogurt, fruit-flavored yogurt (including fruit-on-the-bottom and blended forms), whipped yogurt, granola-topped yogurt, drinkable yogurt, frozen yogurt, and Greek yogurt with varying fat contents (regular, low fat, and non-fat).

Ingredients of Yogurt

• Yogurt is a dairy product that includes a variety of ingredients.
• The primary ingredient is milk, to which sweeteners, stabilizers, fruits, flavors, and bacteria are added.
• The type of milk used in yogurt production depends on the desired fat content.
• Whole milk is used for full-fat or regular yogurt, skim milk for fat-free yogurt, and partially skimmed milk for low-fat yogurt.
• The fat content of the yogurt mixture can be adjusted by adding cream or butterfat, while the solid content can be enhanced with skim milk powder and whey protein concentrate.
• Stabilizers are added to the mixture to give yogurt a smooth texture, prevent whey separation, and evenly distribute the ingredients. Sweeteners are included to enhance the flavor and aroma of yogurt.

Manufacture of Yogurt

Yogurt is made through several steps: blending, pasteurization, inoculation and fermentation, and cooling.

1. Pasteurization

• This is the first step to ensure the product's safety.
• During pasteurization, all pathogenic bacteria in the milk are killed, significantly reducing the number of other organisms and inactivating the milk's enzymes.
• Generally, yogurt is pasteurized using a high-temperature, short-time heat treatment with a long holding time.
• Heat treatment denatures whey proteins, creating optimal conditions for yogurt culture growth.
• Denaturing 80%-85% of whey proteins improves their water-binding capacity, reducing free whey separation and enhancing yogurt consistency and viscosity.

2. Inoculation

• After pasteurization, the yogurt mixture is cooled to 43-46°C.
• Then, 2-3% of yogurt starter culture bacteria are added to the mixture, usually Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in a 1:1 ratio.
• A constant incubation temperature is maintained throughout the yogurt manufacturing process.
• As the yogurt's pH approaches 5.0, microorganisms begin to operate, gradually dominating the fermentation process until the desired pH and acidity are reached.
• The process terminates at 4°C, but the culture remains alive with limited growth ability.
• During fermentation, lactic acid bacteria convert lactose into lactic acid, aiding in the coagulation of milk proteins and the production of volatile compounds.

3. Cooling

• The final step is cooling, which consists of two phases.
• As the coagulum temperature drops rapidly below 10°C, fermentation is inhibited, producing yogurt with low viscosity.
• In the second cooling phase, the coagulum temperature decreases rapidly to less than 20°C, and then the yogurt is further cooled to 5°C (storage temperature) with increased viscosity.
• Upon manufacturing, set yogurts are directly transferred to cold storage for chilling, whereas stirred yogurts are first cooled by agitation before being filled.

Microbiology of Yogurt

• The production of yogurt starts with selecting high-quality milk that meets the required microbiological and chemical standards.
• Typically, milk is heated to a high temperature, between 85°C and 90°C, for a short duration to sterilize it and denature the whey proteins.
• This step ensures that any unwanted microorganisms, which could spoil the yogurt, are eliminated.
• After sterilization, the milk is cooled to 43°C to 46°C, the ideal temperature for the growth of Lactobacillus bulgaricus and Streptococcus thermophilus, which are commonly used in yogurt production.
• When added to milk as a mixed culture or separately, these bacteria ferment lactose.
• As the bacteria consume lactose, they produce lactic acid, lowering the milk’s pH and coagulating the milk proteins, creating a solid gel-like texture.
• Acidification is the key microbiological process in yogurt production, responsible for its characteristic thick and tangy texture.
• The fermentation process usually lasts four to eight hours, during which bacteria continue to consume lactose and produce lactic acid, further acidifying and thickening the yogurt.
• To ensure optimal fermentation and achieve the desired acidity and texture, the temperature and pH of the mixture are carefully controlled.
• Once the desired acidity and texture are reached, the yogurt is cooled to halt fermentation and stabilize it.
• At this stage, ingredients such as fruit, honey, or granola can be added for flavor, sweetness, or texture.
• The yogurt is then packaged and distributed for consumption.

Types of Yogurt

Based on the physical nature

1. Set yogurt
2. Stirred yogurt

Based on Flavor

1. plain/natural yogurt
2. Flavored yogurt

Based on the production method

1. Pasteurized and UHT yogurt
2. Frozen yogurt
3. Dried yogurt/yogurt powder
4. Herbal yogurt

Health Benefits of Yogurt

• Yogurt containing active cultures may benefit gut health.
• Certain probiotic strains in yogurt may boost the immune system.
• Consuming yogurt may help prevent high blood pressure and osteoporosis.
• As a high-protein food, yogurt can aid in post-workout recovery.
• The probiotics in yogurt can improve digestion, metabolic health, and immunity, and may also delay or prevent the onset of cancer.
• Individuals who are lactose intolerant can often tolerate yogurt due to its natural protein content.
• Eating yogurt can promote fat burning and may protect against colon cancer.
• Yogurt may reduce the risk of vaginal infections and strengthen skin collagen.
• In addition to protecting against Helicobacter pylori, yogurt also enhances the immune system.
• Yogurt consumption can improve skin health.
• Yogurt contains organic acids, bacteriocins, diacetyl, and hydrogen peroxide, which act as preservatives and inhibit the growth of harmful bacteria.

Harmful effects of Yogurt

• Some people may have difficulty digesting lactose, which is present in yogurt. After consuming yogurt, individuals who are lactose intolerant may experience symptoms such as bloating, gas, and diarrhea.
• Proteins in yogurt can trigger mild to severe allergic reactions in some individuals.
• Yogurts with added sugar can contribute to weight gain, diabetes, and other health issues.
• Improperly handled or stored yogurt can become contaminated with harmful bacteria, potentially leading to foodborne illnesses.
• The high calcium content in yogurt can interfere with the effectiveness of certain medications, such as antibiotics, if taken together.