Frederic Melton
Yeast plays a significant role in the production of cheese, particularly in the development of its flavour and texture. Yeast is a eukaryote, meaning it contains an identifiable nucleus, and most yeast contain chitin, which gives them a rigid structure. Yeast grows well in acidified environments, and certain strains can produce volatile compounds during fermentation, resulting in undesirable fruity or vinegar-like flavours. Yeast is essential to the cheesemaking process, with some cheeses harbouring up to 30 different yeast species.
| Characteristics | Values |
|---|---|
| Role in cheese-making | Yeast is essential to the cheesemaking process, contributing to the development of flavor and texture. |
| Yeast species | Debaryomyces hansenii, Geotrichum candidum, Kluyveromyces marxianus, Saccharomyces cerevisiae, Candida intermedia, Candida xylopsoci, C. inconspicua, Galactomyces candidus, Pichia kudriavzevii, Trichosporon lactis, Y. lipolytica |
| Growth environment | Yeast can grow in low-moisture environments, with some species thriving at water activity levels as low as 0.61. |
| Spoilage | Yeast contamination can alter flavor, texture, and overall product quality, leading to off-flavors, gas production, and changes in texture. |
| Control strategies | Controlling yeast contamination requires understanding growth parameters and spoilage mechanisms, as well as implementing process monitoring strategies. |
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What You'll Learn
Yeast is essential to cheese-making
Yeast is added to cheese during the ripening process, contributing to the formation of the cheese rind. The rind comprises a complex community of bacterial and fungal species, including yeast, which jointly develop the typical characteristics of the various cheese varieties. The specific yeast species with the highest prevalence on surface-ripened cheeses are Debaryomyces hansenii and Geotrichum candidum, but up to 30 species can be found. In the cheese core, only lactose-fermenting yeasts, such as Kluyveromyces marxianus, are expected to grow.
Yeasts have an indispensable impact on the development of cheese flavour and texture because of their deacidifying, proteolytic, and/or lipolytic activity. They are used in the production of surface-ripened cheeses and as adjunct cultures in the vat milk to modify ripening behaviour and flavour. In certain specialty cheese processes, yeasts are essential by contributing to the development of distinct flavours and textures. For example, in artisan or probiotic cheeses, Saccharomyces cerevisiae is used alongside lactic acid bacteria to enrich the product's texture, flavour, and nutritional profile.
Controlling yeast contamination in cheese production is critical to maintaining product quality and safety. Yeast can contribute to spoilage in cheese through off-flavours, gas production, and changes in texture. Certain yeast strains produce volatile compounds during fermentation, resulting in undesirable fruity or vinegar-like aromas and flavours, particularly in cheeses with high sugar content. Some yeasts produce carbon dioxide and other gases, causing bloating or swelling of the product or packaging, commonly seen in soft cheeses. Yeasts can also influence the texture of cheese by producing enzymes that alter the structure of proteins and fats, leading to sliminess or structural breakdown in soft and semi-soft cheeses.
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Yeast growth parameters and spoilage mechanisms
Yeast is added to cheese to impart specific sensory characteristics to the final product. Yeast growth parameters refer to the optimal conditions under which yeast cells grow and reproduce. These parameters are crucial in cheesemaking to ensure the desired characteristics are achieved.
One of the key yeast growth parameters is pH. Yeast, particularly Saccharomyces cerevisiae, thrives in an acidic environment with a pH of 4. This preference for a slightly acidic environment is taken into account when making cheese with yeast to ensure the yeast grows optimally and contributes to the desired sensory attributes.
Dissolved oxygen (DO) levels also play a significant role in yeast growth. A dissolved oxygen level of 5% provides an ideal condition for yeast cells to proliferate and increase in size. This knowledge is applied in cheesemaking to promote the growth of yeast and enhance the cheese's characteristics.
Yeast growth patterns and rates can be determined using mathematical software and growth curves. These tools help cheesemakers understand the optimal conditions for yeast growth and reproduction, allowing them to create the ideal environment for the yeast to impart the desired traits to the cheese.
Spoilage by yeasts is a significant issue in the food and beverage industry, resulting in financial losses. Yeasts can grow in harsh conditions with low pH, low water activity, and high sugar and/or salt content. They can contaminate most foods and cause spoilage by utilising food components as growth substrates and altering the chemical, physical, and sensory properties of the product. To manage yeast spoilage, good manufacturing practices, including hazard analysis and critical control point (HACCP) analysis, are essential. Additionally, the development of more natural preservatives is critical to combating spoilage and reducing food waste.
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Yeast's role in developing cheese flavour and texture
Yeast plays an indispensable role in developing the flavour and texture of cheese. The microbial community structure in cheese is complex, and the flavour fluctuates greatly. Studying the relationship between microbial structure and flavour formation in cheese is the key to solving the unstable quality and standardised production of cheese flavour. The distinct cheese flavours are produced according to the differences in fermentation conditions and starter cultures, which mainly contain bacterial and yeast starter cultures.
Yeasts are used in the production of surface-ripened cheeses and as adjunct cultures in the vat milk to modify ripening behaviour and the flavour of the cheese. The yeast species with the highest prevalence on surface-ripened cheeses are Debaryomyces hansenii and Geotrichum candidum, but up to 30 species can be found. In the cheese core, only lactose-fermenting yeasts, such as Kluyveromyces marxianus, are expected to grow. The dominance of fermenting yeasts such as K. marxianus and S. cerevisiae suggests that these yeasts contribute to the development of the sensory characteristics of Mozzarella cheese.
The process of surface ripening starts directly after brining with the rapid colonisation of the cheese surface by yeasts. The initially dominant yeasts are acid- and salt-tolerant and are capable of metabolising the lactate produced by the starter lactic acid bacteria and of producing NH3 from amino acids. Both processes cause the pH of the cheese surface to rise dramatically. This so-called deacidification process enables the establishment of a salt-tolerant, Gram-positive bacterial community that is less acid-tolerant.
In recent years, yeasts have also been used as assistant strains in starter cultures to produce cheese. For example, Candida lipolytica is used to produce blue cheese. As adjunct cultures, yeast species contribute to the development of flavour and texture. Fungal starters, such as those containing Pe. albicans and Pe. roqueforti, can have proteolytic and lipolytic activities. Moreover, Pe. albicans produces white hyphae, whereas Pe. roqueforti can accelerate cheese ripening and produce a spicy flavour and a dark green colour.
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Yeast's role in surface-ripened cheeses
Yeast plays a significant role in the development of surface-ripened cheeses. Surface-ripened cheeses, also known as smear cheeses, develop a biofilm called the cheese rind, which is a complex community of bacterial and fungal species, including yeast, that contribute to the cheese's unique characteristics.
The yeast species with the highest prevalence on surface-ripened cheeses are Debaryomyces hansenii and Geotrichum candidum, but up to 30 species can be found. The initial growth of yeast on the cheese surface is rapid, and these yeasts are acid and salt-tolerant, capable of metabolising the lactate produced by the starter lactic acid bacteria. This metabolism causes a rise in the pH of the cheese surface, enabling the growth of a salt-tolerant, Gram-positive bacterial community.
The ratio of surface area to volume in surface-ripened cheeses is an important factor in ripening, as it determines the relative contribution of the surface flora, including yeast, to the flavour of the cheese. The enzymes produced by the surface flora, including yeast, are localised near the cheese surface and contribute to flavour development. Yeasts are also recognised to have an impact on the texture of surface-ripened cheeses due to their deacidifying, proteolytic, and/or lipolytic activity.
The specific yeast species present in surface-ripened cheeses can vary depending on factors such as milk quality, water and salt content, production hygiene, storage temperature, and the location of cheese sampling. Yeasts may also be added as adjunct cultures to vat milk to modify the ripening behaviour and flavour of the cheese. However, yeasts can also be responsible for cheese spoilage, causing off-flavours, discolouration, and other alterations.
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Yeast's role in controlling cheese contamination
Yeast plays a significant role in the cheesemaking process, particularly in the development of flavour and texture. However, it can also cause spoilage, so controlling yeast contamination is crucial for maintaining cheese quality.
Yeast is a diverse group of unicellular fungi that can thrive in various environments, including cheese. In cheese production, yeasts can contribute to the development of distinct flavours and textures. For example, in artisan or probiotic cheeses, Saccharomyces cerevisiae is used alongside lactic acid bacteria to enrich the product's texture, flavour, and nutritional profile. The yeast species with the highest prevalence on surface-ripened cheeses are Debaryomyces hansenii and Geotrichum candidum, but up to 30 species can be found.
Controlling yeast contamination is essential to prevent spoilage and ensure product integrity. Yeast contamination can alter the flavour, texture, and overall quality of the cheese. Early detection of yeast contamination is crucial, and this can be achieved through regular sampling and microbiological analyses of raw materials, intermediate products, and finished goods. Hygiene practices, temperature control, and continuous monitoring of raw materials and processes are also crucial for maintaining cheese quality and preventing yeast overgrowth.
Additionally, the source of yeast contamination must be determined to understand its impact on the maturation process. The complex microflora of certain cheese types, such as white brined cheeses, surface-ripened, and blue-veined cheeses, contains a diverse range of yeasts that play a special role in the maturation process. Understanding the growth parameters and spoilage mechanisms of yeast in cheese production is key to developing effective control strategies.
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Frequently asked questions
Yeast is essential to cheese-making. It contributes to the development of the cheese's flavour and texture.
Yeast has a deacidifying, proteolytic, and/or lipolytic activity. This activity causes a rise in the pH of the cheese surface, enabling the growth of a salt-tolerant, Gram-positive bacterial community.
Some common cheese yeast species include Debaryomyces hansenii, Geotrichum candidum, and Kluyveromyces marxianus.
Yeast contamination can occur when unwanted yeast alters the flavour, texture, and overall product quality of the cheese. This can be due to various factors such as the presence of certain yeast strains, high sugar content, and improper process monitoring.
Controlling yeast contamination requires a comprehensive understanding of yeast growth parameters and spoilage mechanisms. Advanced analytical techniques and continuous improvement strategies can help manage yeast contamination and ensure the production of high-quality, safe cheese products.
