2.2 Thermal Processing: Cooking & Reheating Standards

Thermal Processing: Cooking & Reheating Standards

Proper thermal processing is the primary "kill step" in food preparation. While cold storage prevents bacteria from multiplying, thorough cooking and proper reheating are designed to actively destroy vegetative pathogenic bacteria that are present in the food.

Cooking High-Risk Foods

High-risk foods, particularly poultry (chicken, turkey), minced meats (burgers, sausages, kebabs), and stuffed meats, carry a high risk of bacterial contamination not just on the surface, but throughout the core of the product.

The 75°C Core Temperature Requirement

To ensure that food is safe for consumption, the Qatar MOPH mandates a specific time-temperature combination for cooking. High-risk foods must be cooked until the core temperature reaches a minimum of 75°C.

• The Core: The core refers to the thickest part of the food item. This is the area that takes the longest to heat up. If the core reaches 75°C, you can be confident that the rest of the food has also reached or exceeded this temperature.
• The Holding Time: Simply hitting 75°C for a split second is not enough. The core temperature must be maintained at or above 75°C for at least 30 seconds. This duration ensures the thermal destruction of pathogenic bacteria such as Salmonella, E. coli, and Campylobacter.

How to Measure Core Temperature Properly

1. Ensure the probe thermometer is calibrated, clean, and sanitized.
2. Insert the probe into the thickest part of the meat (e.g., the center of a chicken breast or the middle of a burger patty).
3. Ensure the tip of the probe does not touch bone, fat gristle, or the bottom of the cooking pan, as these will give inaccurate, artificially high readings.
4. Wait for the reading to stabilize on the digital display.
5. Verify that the temperature holds at 75°C or higher for the required 30 seconds.
6. Clean and sanitize the probe immediately after use.

Reheating Standards

Reheating previously cooked food carries significant risks. When food is cooked, cooled, stored, and then heated again, it passes through the Temperature Danger Zone (5°C to 63°C) multiple times. Furthermore, some bacteria can survive the initial cooking process in the form of spores, which can germinate and multiply during the cooling and storage phases.

The 75°C Reheating Rule

Because of these elevated risks, reheating is treated as a critical control point. Any previously cooked food that is being reheated for hot holding or immediate service must be rapidly heated to a core temperature of at least 75°C.

• Rapid Reheating: The reheating process must be fast. You want to push the food through the Temperature Danger Zone as quickly as possible so bacteria do not have time to multiply.
• Equipment: Always use appropriate cooking equipment to reheat food (e.g., ovens, stovetops, steamers, microwaves).
• PROHIBITION: You must never use hot holding equipment (like a bain-marie, soup kettle, or chafing dish) to reheat food. Hot holding equipment is designed only to maintain the temperature of already hot food; it does not have the power to rapidly heat cold food to 75°C, meaning the food will sit in the Danger Zone for hours, becoming highly dangerous.

The "Reheat Once" Rule

Food that has been cooked, cooled, and reheated must only be reheated once.

If you reheat a batch of beef stew for lunch service, any leftover reheated stew at the end of the service must be discarded. You cannot cool it down again and reheat it a second time for dinner. Multiple trips through the Danger Zone dramatically increase the risk of severe bacterial growth and toxin production that cannot be destroyed by further heating.

Microwave Cooking and Reheating

Microwave ovens heat food differently than conventional ovens. They heat via electromagnetic waves that excite water molecules, which can result in uneven heating, leaving "cold spots" in the food where bacteria can survive.

To ensure safety when cooking or reheating in a microwave, follow these specific rules:

1. Stir and Rotate: Food must be stirred, turned, or rotated halfway through the cooking/reheating process to ensure even heat distribution.
2. Target Temperature: The food must achieve an internal temperature of at least 75°C throughout.
3. Resting Time: This is a crucial and often forgotten step. After the microwave cycle finishes, the food must be allowed to rest for at least 2 minutes. During this resting time, thermal conduction continues, allowing the heat to equalize throughout the product, eliminating any cold spots and completing the bacterial destruction process.

Scenario Example: A line cook takes a tray of cold, precooked lasagna from the chiller (at 4°C) and places it directly into a bain-marie (hot holding unit) that is set to 70°C, expecting it to be ready for service in an hour. Correction: This is highly dangerous. The bain-marie will slowly warm the lasagna, keeping it squarely in the optimum bacterial growth range (20°C-50°C) for a long period. The cook must first reheat the lasagna in a conventional oven until the core reaches 75°C, and then transfer it to the preheated bain-marie for holding.