Sous Vide.
A steak in a 56 °C bath is never more than 56 °C anywhere. It cannot be overcooked; it can only be under-timed.
In ordinary cooking the heat source is far hotter than the target, and timing is everything (XV.2). In sous vide ("under vacuum") the food is sealed in a bag and held in water kept at exactly the final temperature wanted, say 56 °C for medium-rare beef. Heat flows in until the whole piece reaches the bath temperature and then stops: the result is the same doneness from edge to edge, with no grey band and very little juice lost, and it can be held for some time without overcooking.
Two times matter. The heating time grows with the square of the thickness (II.2): a 2 cm steak is at temperature within the hour, a 5 cm one takes three or more. And at temperatures below the instant-kill points, the food must be held long enough for a safe log reduction (XII.6) — at 60 °C chicken needs about half an hour after its centre arrives. Then the surface, pale and wet, is dried and seared hard for a minute (XV.7). Sous vide needs an accurate circulator and tested tables: Douglas Baldwin's guide is the standard reference. The workshop times a bath.
Below: minutes for the centre of a slab of the thickness you choose to come within 0.5 °C of a bath at the temperature you choose (thermal bench), for beef and for chicken, and for chicken the extra hold for a 7-log Salmonella reduction (course fit to the FSIS tables).
- Explain equilibrium cooking.
- Time a bath by thickness.
- Add the hold time for safety at low temperatures.
- Finish sous-vide food with a sear.
Time by thickness, then hold
In this model a 20 mm steak comes up to a 56 °C bath in about 49 min and a 50 mm one in 3 h 27 min — the square law again. Chicken at 60 °C needs, after its centre arrives, a further 27 minutes for a 7-log Salmonella reduction; at 64 °C, 5. Leaving food in the bath for a while beyond those times does no harm to doneness, though after several hours textures soften.
Practical sous vide. Season and seal the food (a zip bag with the air pushed out by lowering it into water works); use a circulator that holds its temperature to a few tenths of a degree; start timing when the bath is at temperature; follow a tested table for thickness and temperature; dry the surface well and sear very hot for under a minute a side. Do not use sous vide to hold food in the danger zone (below about 54 °C) for long; and chill and refrigerate anything not eaten at once, or keep it in the bath.
If you have a circulator, cook two steaks of different thickness at 56 °C and check each with a thermometer every 15 minutes. Note how much longer the thick one takes.
Terms
- Sous vide
- Cooking sealed food in a water bath at the final temperature wanted.
- Come-up time
- Time for the centre to reach the bath temperature.
- Hold time
- Extra time at temperature for a safe log reduction.
- Circulator
- A heater and pump that hold a water bath at an exact temperature.
Sources
- D. E. Baldwin, A Practical Guide to Sous Vide Cooking (2008–2012) and "Sous vide cooking: a review", Int. J. Gastron. Food Sci. 1, 2012.
- USDA FSIS, Time-Temperature Tables for Cooking Ready-to-Eat Poultry Products (7-log Salmonella reduction in chicken, 5% fat), as republished in D. E. Baldwin, A Practical Guide to Sous Vide Cooking, and J. K. López-Alt, The Food Lab.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.