Vol. XXXIII · Modern Techniques and the Frontier Plate 6 of 11sous vide, pasteurisation, low temperature cooking, lethality, D-value, z-value, 7-log reduction, Salmonella, chicken, come-up time, holding time, 54.4 °C, Clostridium perfringens, water bath, time and temperature, BaldwinSH

Pasteurising at Low Temperature.

Chicken breast held at 60 °C for half an hour at the centre is as safe as chicken cooked to 74 °C — and far juicier. The catch is the "at the centre".

A pathogen's death is a rate, not a threshold (XII.5, XII.6). Each D-value is the time to kill 90 % of the population at a given temperature; for Salmonella in chicken it is a few minutes at 60 °C and falls about tenfold for every 5–6 °C hotter (the z-value). The USDA's 74 °C for poultry is the temperature at which a 7-log reduction is effectively instant; lower temperatures reach the same reduction with time. Food-safety tables for poultry list these equivalents — about 27 minutes at 60 °C, a few minutes at 65 °C — and sous vide cooking (XVI.7) makes them practical: the water bath holds the meat at exactly the chosen temperature, so the centre can be brought to 60 °C and kept there.

Two cautions make it safe. First, time is counted from when the centre reaches the bath temperature, not from when the bag goes in; thick pieces take an hour or more to come up (II.2), and the thickness, not the weight, sets that time. Second, never cook for long below about 54.4 °C (130 °F): between roughly 40 and 52 °C Clostridium perfringens can multiply, and its spores survive pasteurisation, so food held there for hours, or cooled slowly afterwards, is dangerous (XII.4, XXXI.7). Pasteurised food is not sterile: it must be eaten at once or chilled fast and kept cold. The workshop pasteurises chicken.

Below: for a chicken breast of the thickness you choose in a water bath at the temperature you choose, the minutes for the centre to come up to temperature (thermal bench), the holding time for a 7-log reduction of Salmonella at that temperature (course D- and z-values for Salmonella in chicken), and the total.

What you will learn
Workshop
Come-up: thermal bench, chicken-breast slab of the chosen thickness from 5 °C in a water bath, time for the centre to reach within 0.5 °C of the bath. Hold: course D-value for Salmonella in chicken (D60 ≈ 3.9 minutes, z ≈ 5.4 °C), 7-log reduction, consistent with the USDA poultry time–temperature tables. Minimum bath temperature 54.4 °C (Baldwin; FDA practice).

Time at the centre is what counts

For a 7-log kill of Salmonella in chicken the course model needs about 3 minutes at 65 °C, 27 at 60 °C and 230 at 55 °C. Add the come-up: a 25 mm breast takes about 70 minutes to reach 60 °C at the centre, a 40 mm one about 146. So a 25 mm breast cooked at 60 °C needs about an hour and a half in total — and a thick one far longer, which is why sous vide guides give times by thickness, not weight.

Practical rules: buy a reliable circulator and check it with a calibrated thermometer (I.4); season and seal the meat, removing air so the bag sinks; start in a bath already at temperature; time from the come-up table for the thickness, then the holding time; for chicken use 60–65 °C, for fish 50–55 °C only for food to be eaten at once (that cooks, it does not pasteurise); serve immediately, or chill the sealed bags in iced water and refrigerate, and reheat to temperature before serving. Never hold any food for hours between about 40 and 54 °C.

At the stove

Cook two chicken breasts sous vide, one at 60 °C and one at 70 °C, each for its proper time. Compare their texture and juiciness.

Douglas Baldwin's free online Practical Guide to Sous Vide Cooking, first posted in 2008, worked through the pasteurisation tables for home cooks and set many of the times and minimum temperatures now repeated in recipes worldwide.

Terms

D-value
Time at a temperature to kill 90 % of a microbe.
Come-up time
Time for the centre to reach the bath temperature.
7-log reduction
Killing all but one in ten million.
Pasteurised
Pathogens reduced to safe levels; not sterile.
Pasteurisation is time × temperature: 7 logs of Salmonella in chicken take about 27 min at 60 °C, seconds at 74 °C. Count from when the centre reaches the bath (thickness sets the come-up). Never linger below 54.4 °C. Pasteurised is not sterile: eat or chill at once.

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.