Randy Chandler
Cheese is a beloved dairy product that comes in a variety of textures and flavours. The process of cheesemaking involves removing water from milk, breaking down milk proteins and fats, adding salt, and allowing the cheese to ripen. This process is aided by bacteria, which play a crucial role in converting milk sugars into lactic acid, contributing to flavour development, and forming the distinctive holes in some cheeses. Traditional cheesemaking relied on naturally occurring bacteria, but modern methods often use controlled inoculation with specific bacteria cultures. These bacteria, along with yeasts and moulds, create a unique ecosystem within each variety of cheese, resulting in the diverse flavours and textures that we enjoy today.
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What You'll Learn
Bacteria converts milk sugars into lactic acid
Cheese is a beloved food item incorporated into many cuisines and used as an ingredient in cooking or consumed directly as an appetizer or dessert. The process of making cheese involves four key ingredients: milk, salt, rennet (or another coagulant), and microbes. The microbes involved in cheese-making include a variety of bacteria, yeast, and filamentous fungi (molds).
Lactic acid bacteria (LAB) are a type of bacteria that play a crucial role in cheese production. These bacteria are responsible for converting milk sugars, specifically lactose, into lactic acid. This conversion is a metabolic process known as lactic acid fermentation. During this process, LAB ferment sugars, such as glucose, and convert them primarily into lactic acid. The production of lactic acid lowers the pH of the cheese, creating an environment that is inhospitable to many spoilage organisms. This not only helps preserve the cheese but also contributes to its delicious flavor.
There are two main families of lactic acid bacteria: lactococci and lactobacilli. Lactococci are sphere-shaped bacteria that produce lactic acid, while lactobacilli are rod-shaped and perform the same function. Streptococci, another type of bacteria, also play an important role in initial cheese ripening and are crucial in yogurt-making.
In traditional cheese-making, cheesemakers relied on naturally occurring LAB in milk. However, modern cheese production often involves inoculating milk with industrial starter cultures, which are specifically chosen groups of bacteria that ensure consistent acid production. These starter cultures can be classified as mesophilic, which thrive in temperate conditions, or thermophilic, which prefer higher temperatures. The temperature used in the cheese-making process is dictated by the optimal growth temperature of the microbes in the starter culture.
The process of converting milk sugars into lactic acid is not limited to cheese production. It is also observed in the production of yogurt, where bacteria such as Lactobacillus bulgaricus and Streptococcus thermophilus are used to ferment milk and produce lactic acid. This lowers the pH of the milk, causing it to congeal and inhibiting the growth of harmful bacteria.
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Bacteria breaks down milk proteins
Cheese is a dairy product with a range of flavours, textures, and forms. It is made by coagulating the milk protein casein. The process of making cheese involves separating milk into solid curds and liquid whey by coagulating the casein protein in milk. The solid curds are then separated from the liquid whey and pressed into finished cheese.
The process of converting milk to cheese involves breaking down milk proteins (caseins) and fats. Bacteria play a crucial role in this process. Firstly, milk is acidified to separate the curds and whey and control the growth of undesirable bacteria. Special 'starter' bacteria are added to the milk to initiate this step. These bacteria convert lactose (milk sugar) into lactic acid, lowering the milk's pH and inhibiting the growth of spoilage organisms.
The specific bacteria used for this process depend on the desired cheese variety. Mesophilic bacteria, which thrive at room temperature but die at higher temperatures, are used to make mellow cheeses such as Cheddar, Gouda, and Colby. On the other hand, thermophilic bacteria, which thrive at higher temperatures of around 55°C, are used to make sharper cheeses like Gruyère, Parmesan, and Romano.
During the ripening or ageing process, bacteria continue to break down milk proteins, further altering the flavour and texture of the cheese. The proteins break down into medium-sized pieces (peptides) and then into smaller pieces (amino acids). These amino acids can be further broken down into highly flavoured molecules called amines, contributing to the complex flavours of aged cheeses.
Additionally, some cheeses have additional bacteria or moulds intentionally introduced before or during ageing. These microbes might be allowed to settle naturally in the aging room, or more commonly today, prepared cultures are used to ensure consistent results. Examples of cheeses that use these additional microbes include Brie, Camembert, Roquefort, Stilton, Gorgonzola, and Limburger.
Overall, the breakdown of milk proteins by bacteria is a fundamental step in cheesemaking, influencing the final texture, aroma, and flavour of the cheese.
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Bacteria influences cheese texture and flavour
Cheese is a dairy product with a range of flavours, textures, and forms. It is produced by coagulating the milk protein casein. The solid curds are then separated from the liquid whey and pressed into finished cheese. The basic principles of cheese-making include the removal of water from milk, the breakdown of milk proteins (caseins) and fat, the addition of salt, and an optional ripening period.
The bacteria used in cheese-making play a significant role in determining the texture and flavour of the final product. Firstly, bacteria are responsible for converting milk sugars into lactic acid, which lowers the pH of the cheese and inhibits the growth of unwanted bacteria. This process is essential for the formation of solid curds, which give cheese its characteristic texture. Different types of bacteria used in this process include mesophilic bacteria, which thrive at room temperature and are used in mellow cheeses like Cheddar, and thermophilic bacteria, which thrive at higher temperatures and are used in sharper cheeses like Parmesan.
Secondly, bacteria influence the flavour of cheese, especially during the ripening process. As cheese ripens, bacteria break down milk proteins into smaller pieces, creating highly flavoured molecules called amines. At each stage of ripening, more complex flavours are produced. Certain bacteria, such as Propionibacterium freudenreichii in Swiss cheese, are known for producing distinctive flavours and aromas. For example, Brevibacterium linens, commonly found in surface-ripened cheeses, is responsible for the strong aroma of many cheeses.
Additionally, the combination of different bacteria, yeast, and moulds creates unique flavours and textures in cheese. Traditional cheese-making methods often involved using naturally occurring bacteria from the environment or previous batches, resulting in a diverse microbial ecosystem within the cheese. However, modern cheese-making practices often use controlled inoculation with specific starter cultures, reducing microbial diversity and potentially impacting the complexity of flavours.
In conclusion, bacteria play a crucial role in cheese-making by influencing both texture and flavour. The specific types of bacteria used, the ripening process, and the interaction of bacteria with other microbes all contribute to the distinctive characteristics of different cheeses.
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Bacteria is added to milk to start the cheesemaking process
Cheese is a dairy product with a range of flavours, textures, and forms. It is produced by coagulating the milk protein casein. The milk used is usually sourced from cows, goats, sheep, or water buffalo. The cheesemaking process involves removing water from milk, breaking down milk proteins (caseins) and fats, adding salt, and an optional ripening period. The basic principles of cheesemaking have remained unchanged, but modern cheese production uses scientific knowledge to create consistent, high-quality products.
The cheesemaking process involves separating milk into solid curds and liquid whey by coagulating the casein protein in milk. Milk is usually acidified, and either the enzymes of rennet or bacterial enzymes are added to cause the casein to coagulate. The solid curds are then separated from the liquid whey and pressed into finished cheese. The liquid whey is drained away, and the curds are salted, shaped, and left to ripen in a controlled environment. Microorganisms are used in each step of this process and determine the flavour and texture of the final cheese.
Bacteria are added to milk to start the cheesemaking process. These "starter" bacteria convert the lactose (milk sugar) to lactic acid and lower the milk's pH. There are two types of bacteria used for this process: mesophilic and thermophilic. Mesophilic bacteria thrive at room temperature but die at higher temperatures. They are used to make mellow cheeses such as Cheddar, Gouda, and Colby. Thermophilic bacteria thrive at higher temperatures, around 55°C, and are used to make sharper cheeses such as Gruyère, Parmesan, and Romano.
The type of bacteria used depends on the desired cheese variety. For example, Swiss cheese and Gouda have pronounced eye (hole) formation due to the action of certain bacteria. Propionibacterium freudenreichii ssp. shermanii is a specific bacterium that converts lactic acid into carbon dioxide, propionic acid, and acetic acid. The carbon dioxide seeps into the cheese body and produces the eyes. The other products of Propionibacterium metabolism also give Swiss cheese its characteristic flavours.
In addition to the starter bacteria, some cheeses have additional bacteria or moulds intentionally introduced before or during aging. These microbes might be already present in the aging room, or prepared cultures may be used to ensure consistent results. Examples of cheeses with added bacteria or moulds include Brie, Camembert, Roquefort, Stilton, Gorgonzola, and Limburger.
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Yeast, a type of bacteria, is used in mouldy and surface-ripened cheeses
Yeast is a type of single-celled fungus, not a bacterium. It is used in the production of alcoholic drinks, like wine and beer, as well as in bread-making.
In cheese-making, yeast is commonly used in mouldy and surface-ripened cheeses. It is also naturally present in many natural rind cheeses. Yeast plays an important role in the aging process of many cheeses. In some cheeses, there is a careful balance of yeast, mould, and bacteria that give rise to natural rinds.
Yeast is a chemoorganotroph, meaning it uses organic compounds as a source of energy and does not require sunlight to grow. It obtains carbon mostly from hexose sugars, such as glucose and fructose, or disaccharides like sucrose and maltose. Some yeast species can metabolize pentose sugars, alcohols, and organic acids. Yeast species have different temperature ranges in which they grow best. For example, Leucosporidium frigidum grows at −2 to 20 °C (28 to 68 °F), while Candida slooffi grows at 28 to 45 °C (82 to 113 °F).
Yeast is also used in the production of sweet carbonated beverages, similar to beer, but with less alcohol content. Examples include root beer and kvass, a drink popular in Eastern Europe. Additionally, yeast is used as an ingredient in foods for its umami flavour, similar to monosodium glutamate (MSG). Products like Vegemite and Marmite are made commercially using yeast extract, which is created through a process called heat autolysis.
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Frequently asked questions
The most common types of bacteria used to make cheese include Lactococcus, Lactobacillus, Streptococcus, and Propionibacterium freudenreichii.
These bacteria are often referred to as "starter cultures" as they play a crucial role in converting milk sugar (lactose) into lactic acid, lowering the pH of the cheese and inhibiting the growth of spoilage organisms. They also contribute to the development of flavour and texture in the cheese.
In traditional cheesemaking, bacteria were naturally present in the milk or recycled from an earlier batch's whey. Today, it is common to inoculate milk with industrial starter cultures, which are specifically chosen for cheesemaking to ensure consistent acid production.
