How safe is sous vide and low-temp cooking?

Vacuum packing food inside airtight bags and then cooking it in a water bath at around 55-60°C for a number of hours is used by many top restaurants as a way of cooking food evenly through, maintaining its juiciness and not overcooking the outside. But how safe is the food cooked under these conditions? Especially as recently there has been an increase in the number of sous vide foods being cooked at lower temperatures - down to 42°C.

The Institute of Food Research (IFR) in the UK has been looking at this for the Food Standards Agency. While many chefs are attracted to the precise nature of the temperature control and use the technology to create new textures and flavours by manipulating the behaviour of food components such as proteins, starches and fats, the microbial safety of the cooked food must be paramount.

Much data has been collected on how well food poisoning bacteria grow and survive in different foods at different temperatures - and this data has been collected together and made available through ComBase, a BBSRC-supported National Capability based at IFR. Food manufacturers and academics regularly consult ComBase’s extensive database of microbial growth information.

Most data on microbial growth in food is based on temperatures below 40°C, with studies focusing on how bacteria grow at ambient temperatures, eg, during storage. Other studies have looked at the temperatures at which bacteria are killed, usually above 55-60°C. Lack of information in the range of about 40 to 60°C makes it very difficult for cooks, manufacturers, regulators and enforcement officers to calculate the lethality of such low-temperature heat treatments and judge the risk of foods containing pathogens.

To address this issue, Dr Sandra Stringer and colleagues at the IFR have gathered the information needed to properly assess the hazards associated with lower temperature cooking. The scientists also carried out a feasibility study on extending models in the ‘Combase Predictor’ database. Specifically, they investigated how much work would be needed to upgrade the ComBase database to model the hazards E. coli, Salmonella and L. monocytogenes between around 40 and 60°C. This would help ensure that the safety assessment for sous vide foods is consistent, effective and commensurate with any risk to public health.

This work was carried out as part of a project for the Food Standards Agency (FSA) to provide the best information on this issue and propose a way forward to fill the knowledge gap. The full report is available on the FSA website.

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