Food Safety

Microbial Safety Study of Sous Vide.

QIB Extra completed a short research project determining the safety of current sous vide cooking practices used in Ireland and their safety.
Sous vide, French for “under vacuum”, is a process of cooking in vacuum packed plastic pouches under precisely controlled time and temperature conditions, usually via submersion in a water bath.
Vacuum packaging removes the air and seals the food within the heat-stable pouch, resulting in a reduced oxygen or anaerobic environment.  This facilitates efficient heat transfer to the food product and can increase the shelf-life of the product by limiting the growth of spoilage microorganisms.  Sealing the food product also reduces the risk of post-cooking contamination and prevents evaporative loss of moisture.  The precise temperature control of sous vide regimes also improves reproducibility of the final product, offering greater control of final product taste and texture in comparison with traditional cooking techniques.
Sous vide processed foods can be broadly classified according to the heat treatment applied:

  1. Lightly processed – heat treatment is insufficient for microbial inactivation; survival of vegetative pathogens and parasites present in the raw food product is probable.  The survival of these organisms considerably limits shelf life, therefore the microbiological quality of the raw product is critical.  Safety should be assessed on a case-by-case basis.
  2. Processed at 70°C for 2 min (or equivalent) – based on a 6 log inactivation of Listeria monocytogenes, considered the most heat resistance of the vegetative foodborne pathogens which can also survive and grow at refrigeration temperatures.  Shelf life of these products is limited to 10 days, as the restriction of oxygen and lack of microbial competition provides a favourable environment for psychrotrophic anaerobic spore forming organisms, such as non-proteolytic Clostridium botulinum and psychotrophic Baccilus cereus.  
  3. Processed at 90°C for 10 min (or equivalent) – based on a 6 log inactivation of spores of non-proteolytic C. botulinum. Required for extended shelf life (>10 days) i.e. cook-chill foods.  
  4. Cooked – cooked to acceptable taste, texture and appearance but may not be pasteurised.  These treatments are most likely encountered in home sous vide, restaurants and within the wider catering industry.  This includes a wide variety of time-temperature heat treatments.  
Cooked sous vide methods are increasingly used within restaurants and the catering industry.  Where the time/temperature combinations deviate from traditional pasteurisation, there may be implications for the safety of the food product, highlighting the significance of understanding the ability of foodborne pathogens to survive lower temperature cooking processes.  Although temperature/time combinations have been established for temperatures between 60 and 69˚C, microbial inactivation data is insufficient at sub 60˚C.

When assessing the safety of sous vide cooking at temperatures below 60˚C for products undergoing significant storage at refrigerates temperatures, the main pathogen of concern is Listeria monocytogenes as this organism demonstrates the most heat resistance of the vegetative foodborne pathogens and can survive and grow at refrigeration temperatures.  This is especially relevant for cook-chill sous vide, which involves refrigerated storage and potential heat regeneration following the cooking stage.
For cook-serve sous-vide regimes, where the food product is either served immediately following sous vide cook, or rapidly chilled, stored and consumed within 2 days; Salmonella, and verocytotoxigenic Escherichia coli are of primary concern. Furthermore, applied temperatures below 55°C could promote spore germination and subsequent growth of Clostridium perfringens and Bacillus cereus. Therefore the increased risk of foodborne illness with these organisms need to be considered in products cooked this way.

The results from this study helped the Food Safety Authority of Ireland publish a catering fact sheet on ‘Sous Vide and Food Safety’. To take a look at the fact sheet click here.
 Do you have a product that needs validation against pathogens? Head to our Food Safety page for more information or contact us on +44 (0) 1603 255432 or to discuss your project further.

Applied Contract Research and Analytical Services for Industry

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