Bushra Griffith
Cheese is a food with a high number of living, metabolizing microbes, including bacteria, yeast, and filamentous fungi (molds). The process of making cheese involves manipulating the conditions to encourage the growth of certain microbes while inhibiting others. Cheesemakers control factors such as temperature, humidity, curd size, salt concentration, and oxygen flow to create the desired variety of cheese. Heating milk to different temperatures can determine which bacteria survive, such as Streptococcus thermophilus, which thrives at temperatures above 120°F and is used in making mozzarella. While heating can kill some bacteria, certain types of pathogenic bacteria can survive high cooking temperatures and may require boiling to eliminate.
| Characteristics | Values |
|---|---|
| Is cheese heated to kill bacteria? | Yes, cheese is heated to kill bacteria and control the type of bacteria in the cheese. |
| Temperature to kill bacteria | Bacteria begin to die at 149°F (65°C) and boiling water for one minute is a good precaution. |
| Heat source | The heat generated by microwaves kills bacteria in food. |
| Other methods to kill bacteria | Disinfectants, such as products containing alcohol, can kill bacteria on surfaces. |
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What You'll Learn
- Heating cheese to 149°F (65°C) will kill bacteria
- Boiling water for one minute can also kill bacteria
- Pasteurisation rids milk of pathogens and spoilage organisms
- Heat-loving bacteria like Streptococcus thermophilus is used for mozzarella
- Salt concentration and temperature determine the bacteria in cheese
Heating cheese to 149°F (65°C) will kill bacteria
Heating cheese to 149°F (65°C) will effectively kill bacteria. This temperature is hot enough to destroy bacteria, as they are microscopic, single-celled organisms that begin to die at this temperature.
It is important to note that not all bacteria are harmful, and some are even beneficial to humans. However, pathogenic bacteria can cause illness, and it is crucial to minimize the risk of exposure to these harmful bacteria. Cooking food to the proper internal temperature is an effective way to kill harmful bacteria and reduce the risk of foodborne illnesses.
The optimal temperature for killing bacteria depends on the type of food being cooked. For example, meat must be cooked to a safe internal temperature, which can be determined using a food thermometer. Other factors, such as the shape and thickness of the food, can also affect how evenly it cooks.
Additionally, it is worth noting that some bacteria, such as staphylococcus (staph) and Bacillus cereus, produce toxins that are not destroyed by high cooking temperatures. Therefore, it is important to practice good food safety habits, such as refrigerating perishable foods within two hours and freezing or discarding leftovers within three to four days.
By heating cheese to 149°F (65°C), you can effectively kill bacteria and reduce the risk of potential foodborne illnesses caused by pathogenic bacteria.
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Boiling water for one minute can also kill bacteria
Boiling water is an effective way to kill harmful bacteria and make it safe to drink. This is especially important in emergency situations where regular water service has been interrupted, and local authorities recommend using boiled water.
To effectively kill bacteria, bring the water to a rolling boil, which is a vigorous boil with lots of bubbles. Let the water boil for at least one minute. Then, remove it from the heat source and allow it to cool down. Once cooled, store the water in a clean, tightly secured container.
The boiling process kills or inactivates viruses, bacteria, protozoa, and other pathogens by damaging their structural components and disrupting essential life processes. Bacteria begin to die at 149°F (65°C), but boiling water for one minute is a good precaution to ensure their elimination.
While boiling water is an effective method, it is important to note that it does not destroy all contaminants. For example, heavy metals, salts, and most chemicals will remain unaffected by boiling. Additionally, some bacteria, such as Staphylococcus and Bacillus cereus, produce toxins that are also resistant to high cooking temperatures. Therefore, it is crucial to combine boiling with other disinfection methods, such as using household bleach or iodine, to ensure the water is safe for consumption.
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Pasteurisation rids milk of pathogens and spoilage organisms
Pasteurization is a food preservation process that eliminates pathogens and extends shelf life. Named after French microbiologist Louis Pasteur, pasteurization involves treating packaged foods with mild heat, usually below 100°C (212°F), to destroy or deactivate spoilage organisms and enzymes. This process is widely used in the dairy industry to ensure milk safety and extend its shelf life.
Milk is highly susceptible to microbial growth, and before pasteurization, it was a common source of harmful bacteria, causing diseases such as tuberculosis, Q fever, and typhoid fever. Pasteurization kills these disease-causing organisms, making milk safe for consumption. It targets organisms like salmonella, listeria, E. coli, campylobacter, and influenza, which can contaminate milk even with careful production methods.
The process of pasteurization involves heating milk to specific temperatures for defined durations, with various methods available, including batch and continuous flow pasteurization. Batch pasteurization, also known as vat pasteurization, requires heating every particle of milk to a minimum of 145°F (63°C) for at least 30 minutes. This method ensures the complete destruction of disease-producing organisms and has been used for over a century to protect consumers.
High-Temperature Short Time (HTST) pasteurization, commonly used for milk, involves heating milk to 160.7°F (71.5°C) for 15 seconds. This method ensures milk safety and provides a refrigerated shelf life of about two weeks. Ultra-High Temperature (UHT) pasteurization takes this process further, heating milk to 275°F (135°C) for 1-2 seconds, resulting in the same level of safety as HTST.
Pasteurization is a critical process in ensuring milk safety and reducing the risk of foodborne illnesses. By destroying harmful pathogens and spoilage organisms, pasteurization plays a vital role in the dairy industry, allowing for the safe consumption of milk and dairy products.
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Heat-loving bacteria like Streptococcus thermophilus is used for mozzarella
Heating food to a safe internal temperature is an effective way to kill harmful bacteria. However, some bacteria, like Streptococcus thermophilus, are heat-loving bacteria that thrive at high temperatures. Streptococcus thermophilus, formerly known as Streptococcus salivarius subsp. thermophilus, is a gram-positive, non-motile, non-pathogenic bacterium. It is a member of the thermophilic group of lactic acid bacteria (LAB) and has an optimal growth temperature range of 35-42 °C. This bacterium plays a crucial role in the production of mozzarella cheese and other Italian and Swiss cheeses, such as Emmentaler.
S. thermophilus is traditionally used in combination with one or more Lactobacillus species as a starter culture in the cheese-making process. It is responsible for producing lactic acid, which is essential for fermentation, and it can also synthesise exopolysaccharides (EPSs). EPSs impart a desirable texture and viscosity to the cheese, improving the functional properties of low-fat or part-skim mozzarella. The use of S. thermophilus in cheese-making has increased due to the rising popularity of mozzarella cheese.
The safety of using S. thermophilus in food production has been evaluated, and it has been found to be stable and suitable for industrial use. Its genome sequence reveals that it lacks the virulence regions common to other Streptococcus species, indicating that it has likely adapted to the dairy environment over time. This adaptation reinforces the safety profile of this bacterium for consumption.
In addition to its role in cheese production, S. thermophilus is commonly used in yoghurt manufacturing. It is found in fermented milk products and contributes to their sensory and technological quality. The combination of S. thermophilus with Lactobacillus delbrueckii subsp. bulgaricus is synergistic, as they support each other's growth and provide essential acids for synthesis processes.
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Salt concentration and temperature determine the bacteria in cheese
The presence of bacteria in cheese is influenced by a variety of factors, including salt concentration and temperature. While heating food is a common method to kill bacteria, it is important to note that not all bacteria are affected by temperature. Some bacteria, such as Staphylococcus (Staph) and Bacillus cereus, can produce toxins that are heat-resistant. Therefore, other methods, such as salt concentration, play a crucial role in inhibiting bacterial growth in cheese.
Salt concentration is a critical factor in the safety of cheese products, particularly in inhibiting the growth of bacterial pathogens. Studies have shown that higher salt concentrations are associated with enhanced microbiological safety in cheeses. For example, an increase in salt concentration can reduce the growth of Listeria monocytogenes, a common pathogen found in soft cheeses. This is supported by research on "Turrialba cheese", a Costa Rican fresh cheese, which revealed that Listeria monocytogenes could grow under all tested conditions, including different salt concentrations.
The interaction between salt concentration and temperature influences the behaviour of bacteria in cheese. Listeria monocytogenes, for instance, has been found to have an inverse relationship between the maximum growth rate and salt concentration. However, at the end of the evaluation period, the bacterial population reached high levels, indicating that salt concentration alone may not be sufficient to prevent bacterial growth entirely.
Additionally, the curing process, which involves holding the finished cheese at a specific temperature for an extended period, typically 60 days at 2°C, can also impact bacterial activity. This process assumes that any bacterial pathogens present in fresh cheese will die within the specified time frame. However, it is important to note that the effectiveness of the curing process depends on the acidity (pH) and salt concentration of the cheese.
In summary, while temperature plays a role in inhibiting bacterial growth, salt concentration is a critical factor in the safety of cheese products. Higher salt concentrations generally enhance microbiological safety, but the specific interactions between salt and temperature can vary depending on the type of bacteria present. Therefore, a comprehensive understanding of the complex relationships between salt concentration, temperature, and bacterial behaviour is essential to ensure the safety and quality of cheese products.
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Frequently asked questions
Yes, heating cheese kills bacteria. Bacteria begin to die at 149°F (65°C), but boiling is a good precaution. The optimal temperature for killing bacteria depends on the type of food.
Cheesemakers control the type of bacteria in their cheese by manipulating the temperature and humidity levels. For example, heating milk to over 120°F will kill most bacteria except for heat-loving bacteria like Streptococcus thermophilus, which is used to make mozzarella.
The best way to ensure that your cheese is safe to eat is to cook it to the proper internal temperature. Using a food thermometer is the only way to know if your cheese has been cooked to a safe internal temperature.
