Kamil Perry
Yogurt and cheese are primarily made from bacterial cells, specifically Lactobacillus, Bifidobacterium, and Streptococcus species. These bacteria are prokaryotic cells, meaning they lack a nucleus and other membrane-bound organelles. They play a crucial role in fermenting milk sugars into lactic acid, causing the milk proteins to curdle and form the desired consistency for yogurt and cheese. The process of fermentation also enhances the flavour and texture of the final products. The specific bacteria used and the steps involved can vary depending on the type of yogurt or cheese being produced, resulting in the wide variety of dairy products available today.
Characteristics and Values of the Cells that Make Yogurt and Cheese
| Characteristics | Values |
|---|---|
| Type of cells | Prokaryotic bacterial cells |
| Genera | Lactobacillus, Bifidobacterium, Streptococcus |
| Species | Lactobacillus bulgaricus, Streptococcus thermophilus, Lactococcus |
| Function | Ferment milk sugars into lactic acid, causing milk proteins to denature and form yogurt or cheese |
| Cheese-making process | Coagulating casein protein in milk, separating curds and whey, ripening |
| Yogurt production | Fermenting milk with strains of bacteria |
| Cheese types | Hard, Swiss, fresh, blue vein, Gouda, Brie, Camembert, Emmental, Mozzarella, Provolone |
| Yogurt types | Turkish, stirred, plain |
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What You'll Learn
Yogurt and cheese are made from bacterial cells
The process of making yogurt involves skimming, pasteurizing, and homogenizing the milk before culturing it in a large vat with added fruits and flavors. The milk is then allowed to incubate until it reaches a custard-like state, after which it is cooled. For a thicker Greek-style yogurt, the yogurt is strained to remove the whey, resulting in a thicker consistency.
Cheese formation, on the other hand, starts with milk and a starter culture, which sours the milk and forms curds. A coagulant, rennet, is added, and then the whey protein is removed. The leftover curd is salted to control the formation of lactic acid and preserve flavor. The cheese is then molded, pressed, and left to ripen and mature to the desired taste.
The bacteria used in yogurt and cheese production, such as Lactobacillus bulgaricus and Streptococcus thermophilus, thrive in warm conditions. They convert lactose into lactic acid, creating the distinctive creamy texture and tart flavor of yogurt. This process is also crucial in cheese-making, as the fermentation not only solidifies the milk but also contributes to the unique flavors and textures of different cheese varieties.
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Lactobacillus, Bifidobacterium, and Streptococcus species
Yogurt and cheese are made from bacterial cells, specifically Lactobacillus, Bifidobacterium, and Streptococcus species. These bacteria are prokaryotic cells, meaning they lack a nucleus and other membrane-bound organelles. They are essential to the process of dairy production, as they ferment milk sugars into lactic acid, causing milk proteins to denature and form yogurt or cheese.
Lactobacillus is a key bacterial strain in yogurt and cheese production. Lactobacillus bulgaricus and Lactobacillus plantarum are commonly used in yogurt fermentation. Lactobacillus delbrueckii subsp. bulgaricus is a ubiquitous family of microbes that can ferment glucose into lactic acid in a dairy environment. The ratio of Lactobacillus to other bacterial strains in yogurt starter cultures impacts the fermentation time, pH, viscosity, and other characteristics of the final product. Lactobacillus acidophilus is another important strain, often found in yogurt and other dairy products, as well as fermented foods like miso and tempeh. It is one of the most common types of probiotics, offering health benefits for gut health. However, Lactobacillus strains may not be suitable for individuals with underlying health issues, weakened immune systems, or recent surgeries.
Bifidobacterium species are also used in yogurt and cheese production. Bifidobacterium bifidum is a species of bacteria present in the human gastrointestinal tract and vagina. It can be added as a supplementary starter culture in yogurt production, impacting the concentration of certain compounds and the growth of other bacteria.
Streptococcus species, including Streptococcus thermophilus and Streptococcus lactis subsp. diacetylactis, are commonly used in yogurt and cheese fermentation. Streptococcus thermophilus is a powerful probiotic strain often found in yogurt and cheese. It plays a crucial role in the fermentation process by stabilizing other probiotic bacteria that do not grow well in milk.
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Fermenting milk sugars into lactic acid
Yogurt and cheese are made from bacterial cells, specifically Lactobacillus, Bifidobacterium, and Streptococcus species. These bacteria are prokaryotic cells, meaning they lack a nucleus and other membrane-bound organelles.
When milk is heated and then cooled, these bacteria are introduced as starter cultures. They ferment lactose, the sugar in milk, into lactic acid through a process called fermentation. This process is known as lactic acid fermentation, and it involves the conversion of glucose or other six-carbon sugars into cellular energy and the metabolite lactate, or lactic acid. Lactic acid fermentation is an anaerobic process, meaning it occurs in the absence of oxygen.
During lactic acid fermentation, the bacteria ingest the natural sugars found in milk and release lactic acid as a waste product. This accumulation of lactic acid causes the milk proteins, particularly casein, to denature and form a curd. The curd has a thickened texture for yogurt or a solid mass for cheese. The specific bacteria used and the conditions of fermentation contribute to the unique flavours and textures of different yogurt and cheese varieties.
For yogurt, the milk is typically skimmed, pasteurized, and homogenized before the bacteria are added. The yogurt is then allowed to incubate until it reaches a custard-like state and is then cooled. Cheese formation, on the other hand, involves adding a coagulant called rennet, which is an enzyme, to the milk along with the starter culture. The whey protein is then removed, and the leftover curd is salted to control the formation of lactic acid and preserve the desired flavour. The cheese is then moulded, pressed, and left to ripen.
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The role of milk in yogurt and cheese
Milk is an essential component in the production of yogurt and cheese. It provides the required protein and fat composition necessary for the fermentation process. Milk is a complex system composed of proteins, fats, lactose, and other components that assemble into three distinct physical systems.
The process of making yogurt involves skimming, pasteurizing, and homogenizing milk. The milk is then cultured in a large vat, and fruits and flavors are added. The milk is allowed to incubate until it reaches a custard-like state. The final product is then cooled, resulting in the traditional set or blended yogurt. Yogurt can be made from various types of milk, including bovine, water buffalo, and goat milk. The specific type of milk used can impact the color of the yogurt, with milk containing higher fat content tending to have a slight yellow hue.
Yogurt production relies on bacterial strains such as Lactobacillus bulgaricus and Streptococcus thermophilus, which are added to heated milk and left to sit at warm temperatures. These bacteria convert the lactose in milk into lactic acid, creating the distinctive creamy texture and tart flavor of yogurt. The accumulation of lactic acid causes the milk proteins to denature and form a viscous, semi-solid mass.
Cheese production also involves the use of bacterial cultures and milk. The starter culture sours the milk and forms curds, and a coagulant called rennet is added to aid in the coagulation process. The whey protein is then removed, and the leftover curd is salted to control the formation of lactic acid and preserve the desired flavor. The cheese is then molded, pressed, and left to ripen and mature to the desired taste. Different types of bacteria and molds are used in cheese-making, contributing to the unique flavors and textures of various cheese varieties.
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The process of making yogurt and cheese
Yogurt and cheese are made from bacterial cells, specifically Lactobacillus, Bifidobacterium, and Streptococcus species. These bacteria are prokaryotic cells, meaning they lack a nucleus and other membrane-bound organelles. To make yogurt and cheese, these bacteria are introduced to milk as starter cultures and ferment the lactose (milk sugar) into lactic acid. This process is called fermentation and results in the thickening and curdling of the milk, forming yogurt or cheese.
The Process of Making Yogurt
Yogurt is made by heating milk to just below boiling (around 180-190°F or 200°F) and then cooling it to a warm temperature (around 112-115°F). Live yogurt cultures are then added, and the milk is kept warm while the bacteria turn the milk into yogurt. The number of cultures is not crucial, but different strains offer different health benefits. The milk used can be whole, 2%, or skim, and it can be raw, pasteurized, grass-fed, or homogenized. However, ultra-pasteurized milk is generally not recommended as it is more difficult to work with.
The Process of Making Cheese
Cheese is typically made in factories, and the process varies depending on the type of cheese. However, all cheesemaking follows a general procedure. First, milk is prepared by standardizing the protein-to-fat ratio and pasteurizing or heat-treating it. Then, starter cultures are added to acidify and ripen the milk. A coagulant is added to curdle the milk, creating curds and whey. The curds are stirred, cooked, and washed to further acidify and dry them. The whey is then drained, and the curds are cut and flipped before being salted and shaped. Finally, the cheese is aged, contributing to its unique flavor and texture.
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Frequently asked questions
Cheese is made from bacterial cells, specifically species belonging to the genera Lactobacillus, Bifidobacterium, and Streptococcus.
These bacteria are prokaryotic cells, meaning they lack a nucleus and other membrane-bound organelles. They ferment lactose, the sugar in milk, into lactic acid. This process of fermentation produces the lactic acid that causes milk proteins, particularly casein, to denature and curdle, forming the curds used in cheese production.
Cheesemaking involves coagulating the casein protein in milk and then separating the milk into solid curds and liquid whey. The liquid whey is drained away, and the curds are salted, shaped and left to ripen in a controlled environment.
Some commonly used bacteria include Lactococcus, Lactobacillus, Streptococcus, and Propionibacterium freudenreichii.
Yogurt is made from bacterial cells, specifically Lactobacillus bulgaricus and Streptococcus thermophilus.
