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Monday, May 30, 2011

Low Temperature Cooking - Some Safety Considerations

Note: See References below for links.

Cooking safely should be the goal of all of us that cook for ourselves as well as others.  It's easy to assume we cook safe, but unless we use an accurate thermometer, and also know the length of time a food has been cooked, our assumptions may be incorrect.

Low Temperature Cooking
Low temperature cooking offers us a method of cooking that:
  • can tenderize foods.  We can choose cheaper cuts of meat that are tough and make them tender.
  • retain moisture and fat for a more flavorful experience
  • be convenient

Some important concepts
(Note: a lot of the insight in this section is provided by Douglas E. Baldwin's excellent and well researched book A practical Guide to Sous Vide Cooking.
  • Heating food: the center of the food should reach at least 130°F (54.4°C) within 6 hours to prevent the toxin producing pathogen Clostridium perfringens from multiplying to dangerous levels.  Your heat should be sufficient, for the size of the cut of food you are cooking, to heat to a temperature of 130 dF, or higher, within 6 hours of removing the food from the cooler.  Since larger pieces of food require the heating temperatures to migrate a bigger distance before reaching the center of the food, larger pieces of food will take longer to reach 130 dF than will smaller pieces of food.  If the size of the meat is so large as to preclude the heat from reaching a temperature at or greater than 130 dF within 6 hours at the center of the food, then a higher cooking temperature must be used, or the food should be cut to smaller thicknesses.    [A practical Guide to Sous Vide Cooking]
  • Placing warm, large pieces of food into a refrigerator may take a long time to cool sufficiently to reduce the chance of problem bacterial growth.  Thus, the food should be cooled via a water-ice mixture (50%/50%) in order to quick chill the food.  You can place the food into pouches, such as Zip Lock, removing all or most of the air so the food isn't insulated from the cool water by the air, in order to prevent dilution of the food with the water-ice mixture.
  • Raw or unpasteurized food must never be served to highly susceptible or immune compromised populations. Even for immune competent individuals, it is important that raw and unpasteurized foods are consumed before food pathogens have had time to multiply to harmful levels. With this in mind, the US Food Code requires that such food can only be between 41°F (5°C) and 130°F (54.4°C) for less than 4 hours.  [A practical Guide to Sous Vide Cooking]
  • A refrigerator (not the freezer section) should be set to maintain a temperature at or below 38 dF.  Foods held below 41 dF can retard bacterial growth sufficiently so that the food is safe for up to 10 days.  Foods held below 38 dF can retard bacterial growth sufficiently so the food is safe for up to 31 days.[A practical Guide to Sous Vide Cooking]

Testing Thermometers (future section)

References (future section)

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