Vacuum packaging stops the development of the aerobic flora but does not inhibit the growth of all bacterias. The anaerobic conditions, together with the relatively low temperature heat treatment of sous vide cooking creates an atmosphere in which the pathogen Clostridium perfringens and salmonella can multiply to dangerous levels.
Sous vide prepared food can be divided into three categories:
- raw or unpasteurized food must not be served to highly susceptible or immune compromised populations. For immune competent individuals, raw or unpasteurized food should not be served after been exposed 4 hours long to temperature between 5°C (41°F) and 55°C (131°F).
- pasteurized food. Pasteurization means heat treating the food to reduce the number of vegetative pathogens to a safe level. Pasteurized food must either be eaten immediately or rapidly chilled and refrigerated to prevent the outgrowth and multiplication of Clostridium spores which are very resistant to heat.
- Sterilized food is heat treated to reduce both vegetative microorganisms and spores to as safe level called sterilization (for that you need a pressure cooker to heat the centre of the food to 121°C (250°F) for 2.4 minutes which makes the food being overcooked and taste similar to canned foods).
Sous vide temperature safety zones can be summarized as follow:
- Sterilization zone: > 121°C (250°F) for at least 2.4 minutes
- Assured Pasteurization zone: > 63°C + (145.4°F)
- Start of Pasteurization zone: 60°C (140°F) – 63°C (145.4°F)
- Tolerance zone: 55°C (131°C) – 60°C (140°F)
- Danger zone: 50°C (122°F) – 55°C (131°F)
- Extreme Danger zone: 20°C (68°F) – 50°C (122°F)
- Danger zone: 10°C (50°F) – 20°C (68°F)
- Tolerance zone: 3°C (37.4°F) – 10°C (50°F) most preparation takes place in this temperature range
- Secure zone: < 3°C (37.4°F)
To sum up:
Raw food must not be stored for more than two days before pasteurization and must be cooled below 3°C (37°F) within two hours.
Pasteurized food should be served immediately or stored below 3°C (37°F) and consumed or chilled/refrigerated within a specified time period.
In the framework of Sousvidecooking.org blog experiments we will always cook sous vide above 55°C (131°C) and served food immediately in order to avoid any chilling/refrigerated issues. As a finishing (Maillard reaction that gives flavour) and also for safety purposes (destroy the Clostridium spores with heat superior to 200°C (400°F)) we will sear meats with a blowtorch or in a pan.