Sous vide and low-temperature cooking

Why

Bacteria die according to both temperature and time: the UK FSA lists 70 °C for 2 minutes, 65 °C for 10 minutes and 60 °C for 45 minutes as equivalent, always in the core of the thickest part, not in the water bath. So a chicken breast from a 65 °C bath can be safe without the 74 °C given by US authorities (see the Internal temperature of meat card), but only if the whole piece heats through to that temperature and holds it; the time until the core heats up does not count towards the hold and grows quickly with thickness. Below about 55 °C pasteurisation is uncertain and Clostridium perfringens can multiply in the meat, so Australian authorities advise a bath of at least 55 °C and not holding food at 54.5 °C or less for more than 6 hours. Pasteurisation also leaves bacterial spores alive, and in an oxygen-free bag they can germinate if the food cools slowly or sits long in the fridge. A steak or fish from a bath below 55 °C, or taken out as soon as it has heated through, is therefore not pasteurised and is not for at-risk groups.

How to do it

• Set the bath to at least 55 °C and put the meat in cold from the fridge, in a bag made for cooking; divide thick pieces so the core heats through faster.
• Cook poultry, pork and minced meat so the core holds at least 65 °C for 10 minutes or 60 °C for 45 minutes; check the core temperature with a probe thermometer.
• After cooking, pat the meat dry and sear it as briefly as possible in a very hot pan, so the crust forms before the inside overcooks (see the Searing meat card).
• Chill whatever you will not eat at once in its bag in iced water and refrigerate it (see the Cooling and storing leftovers card); eat translucent fish and unpasteurised meat at once.
• For pregnant women, young children, older people and anyone with weakened immunity, serve only pasteurised or fully cooked meat, and fish cooked to 63 °C.
• Cook fish with a translucent centre only from sea fish sold for eating raw or frozen beforehand against parasites (see the Raw fish: ceviche, tartare, sushi card).

If it goes wrong

Mushy meat that falls apart usually comes from cooking too long or from an acidic or enzyme marinade (see the Marinades: acid, enzymes, yoghurt card); use it in a sauce or filling and shorten the time next time. Pat a grey surface without a crust dry and finish it in a very hot pan or under the grill. If the bath failed during cooking and you do not know how long the meat sat lukewarm, do not rely on reheating: it destroys neither spores nor toxins the bacteria have already made, so throw the meat away. Do not open a swollen bag from the fridge to taste it; throw it away.