Vol. XXXIV · History and Projects Plate 6 of 13project, chicken, sous vide, pasteurisation, 7-log reduction, Salmonella, juiciness, moisture loss, time and temperature, lethality, water bath, design briefSH

Project: Safe and Juicy Chicken.

Chicken breast cooked to 74 °C is safe but loses a fifth of its weight. At 60 °C for long enough it is just as safe and loses a seventh.

Two curves pull against each other (XII.6, XVIII.3). Safety needs enough time at a high enough temperature for the pathogen to be killed — the lethality, here at least a 7-log reduction of Salmonella in chicken at the slowest-heating point, the centre. Juiciness needs the meat to stay cool enough that its proteins do not squeeze out too much water: muscle loses juice increasingly as it passes about 60 °C (VI.5). A hot bath reaches safety quickly but overshoots juiciness; a cool bath keeps the juice but needs a long time to be safe (XXXIII.6).

Your design: the bath temperature and the minutes the breast spends in it, from the fridge. The checks are measured on the thermal and microbe benches together: the log reduction accumulated at the centre, and the fraction of the meat's weight lost as juice. The starting design — a short dip — fails safety.

Below: the centre and surface temperatures of a 25 mm chicken breast in the water bath of your design (thermal bench), the Salmonella log reduction accumulated at its centre (course D- and z-values), the juice lost, and the brief.

What you will learn
Workshop
Thermal and microbe benches: a 25 mm slab of chicken-breast composition (USDA) from 5 °C in a water bath; Salmonella in chicken (course D60 ≈ 3.9 min, z ≈ 5.4 °C) accumulated at the centre; juice loss from the course's muscle water-loss curve, weighted over the thickness.

Lethality is time; juiciness is temperature

A bath at 70 °C for 40 minutes reaches about 12 logs at the centre — safe — but the breast loses about 20 % of its weight: dry. Bring the bath down to about 60 °C and the juice loss falls, but now safety needs time — over an hour and a half for a 25 mm breast, counting the come-up. The brief is met in a window, and the window is wider for thinner pieces.

At home: season the breast, seal it, cook at 60–62 °C for the time your thickness needs (XXXIII.6), then pat dry and sear quickly for colour if you like; or poach gently in barely simmering stock and check the centre with a thermometer (I.4). The same reasoning — enough time at temperature, no hotter than needed — applies to poaching, steaming and roasting, where only the centre's history matters for safety.

At the stove

Cook two chicken breasts of the same thickness, one poached to 74 °C and one held at 60–62 °C for the right time. Weigh them before and after.

The USDA's 74 °C for poultry is set so that a 7-log reduction of Salmonella happens almost instantly; its own time–temperature tables for processors list the lower-temperature equivalents that sous vide cooks rely on.

Terms

Lethality
The log reduction of a pathogen accumulated over a cook.
Juice loss
Weight lost as water squeezed from heated muscle.
Coldest point
The centre: the last part to heat, so the critical one for safety.
Window
The range of designs that meet every check.
Safety is time at temperature (≥ 7 logs at the centre); juiciness falls as the meat passes about 60 °C. Meet both with a moderate temperature held long enough — about 60 °C for well over an hour for a 25 mm breast.

Sources

  1. 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.
  2. 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.
  3. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.