Sous vide is safe when a few specific things are done, and unlike most cooking it depends on procedure rather than judgement.
The Reasons Behind Them
- Pasteurisation depends on time as well as temperature
- Come-up time is additional to holding time and depends on thickness
- Vacuum sealing removes oxygen, which suits Clostridium botulinum
- Its spores survive normal cooking and germinate in the right conditions
- Slow cooling passes food down through the growth range
- And the toxin cannot be seen, smelled or tasted
Equipment that holds temperature stably and keeps bags submerged, of the kind catalogued at https://everie.us.com/, is what makes following those rules practical.
The Core Four
Follow published time-temperature tables, and follow them fully rather than rounding down.
Do not cook below the temperature floor, commonly given as around fifty-four to fifty-five degrees Celsius, for extended periods.
Chill rapidly in ice water if food is not eaten immediately.
Refrigerate below three degrees Celsius and observe published storage times.
The Specific Mistakes
Leaving a bag to cool in the bath. Letting a bag float so part of the food is above the water. Vacuum sealing food and leaving it out to marinate.
Garlic or fresh herbs in oil held sealed at room temperature, which is a documented risk on its own.
Setting a bath below the floor for a long cook because a recipe suggested it.
If a Cook Fails
Food from a bath that stopped for an unknown period should be discarded rather than judged.
There is no reliable way to assess it by looking or smelling.
Vulnerable Groups
Anyone pregnant, very young, older or immunocompromised should follow conventional temperature guidance.
Use a Tested Source
Food safety authorities and reputable references publish the tables.
Do Not Improvise
Which is the whole summary.
Print the Table
And keep it where you cook, rather than looking it up each time.
Never Cool in the Bath
The single most common serious mistake.
Discard After a Failed Cook
Rather than assessing it by eye.
Vulnerable Groups Follow Standard Guidance
Rather than low-temperature methods.
Come-Up Time Is Additional
The holding clock starts when the core reaches temperature, not when the bag goes in.