Module 5 Notes: Flow of Food — Cross Contamination and Temperature Control

Flow of Food

• The flow of food is the path that food takes through your operation.

  • For all food items, this path includes purchasing, receiving, storing, and service.

  • For some items, it may also include other steps like preparation, cooking, holding, cooling, and reheating.

• Food can change safety during the flow (e.g., a frozen item may thaw en route to the supplier's warehouse).

• Once in your operation, food might be stored incorrectly or cooked to the wrong internal temperature, leading to foodborne illness.

• You are responsible for the safety of food at every point in the flow of food.

• Biggest hazards discussed: cross contamination and time temperature abuse (TTA).

• The module focuses on preventing cross contamination and preventing time temperature abuse during the flow of food.

• Temperature control begins with understanding the temperature danger zone and how to keep food out of it.

• The most important tool for preventing TTA is the thermometer; emphasis on how to use and maintain thermometers.

• Question posed: What’s the biggest hazard to food as it flows through the operation? Answer: Cross contamination and time temperature abuse.

• Ethical/practical implication: You must implement and follow policies to protect customers; safety is a professional responsibility.

Cross Contamination

• Cross contamination can happen at almost any point in the flow of food because pathogens move easily.

• Pathogens can move from food or unwashed hands to prep areas, equipment, utensils, or other food.

• Prevention principle: keep raw and ready-to-eat (RTE) foods apart from each other.

• Color-coded cutting boards and utensil handles help keep equipment separate and prevent cross contamination:

  • Red = raw meat

  • Yellow = raw poultry

  • Green = produce

  • Other colors may be available; check with supplier.

• Handling practices shown (evaluate and decide if they prevent cross contamination):

  • Using color-coded cutting boards helps separation of foods.

  • Merely wiping equipment after raw poultry is not enough; wash, rinse, and sanitize all surfaces and utensils before and after each task.

  • Always separate raw meat, poultry, and seafood from unwashed and RTE fruits/vegetables during storage, preparation, holding, and display.

  • Prep raw meat, fish, and poultry at different times from ready-to-eat foods; better yet, prep ready-to-eat foods before raw foods.

  • Clean and sanitize surfaces and utensils between each type of food.

  • Buying foods that require little handling can reduce cross contamination risk.

Time Temperature Abuse (TT A)

• Most foodborne illnesses occur because TCS (time/temperature control) food has been time temperature abused.

• Temperature danger zone (TDZ): food must be kept outside this range as much as possible.

  • TDZ range in Fahrenheit and Celsius:

  • $41^{\circ}\mathrm{F} \le T \le 135^{\circ}\mathrm{F}$

  • $5^{\circ}\mathrm{C} \le T \le 57^{\circ}\mathrm{C}$

• Pathogen growth is faster in a subrange:

  • Most rapid growth between $70^{\circ}\mathrm{F} \le T \le 125^{\circ}\mathrm{F}$

  • $21^{\circ}\mathrm{C} \le T \le 52^{\circ}\mathrm{C}$

• TDZ abuse occurs whenever food is cooked to the wrong internal temperature, held at the wrong temperature, or cooled/reheated incorrectly.

• The longer food stays in the TDZ, the more time pathogens have to grow.

• Rule of thumb: if food is held in the TDZ for $4\ \text{hours}$, you must throw it out.

• Ultimate goal: reduce the time food spends in the TDZ as much as possible.

• What to do to prevent TTA:

  • Put in place good policies and procedures that specify which items to check, how often, and by whom.

  • Ensure food handlers understand what to do, how to do it, and why it matters.

  • Provide the correct kinds of thermometers for staff; consider giving them their own thermometers.

  • Use timers in prep areas to monitor how long food has been in the TDZ.

  • Record temperatures regularly and note the times; print simple forms and post them near coolers/freezers and near prep, cooking, and holding equipment.

  • Limit the amount of food removed from a cooler during prep to reduce TDZ exposure.

  • Define corrective actions if standards are not met (example: if holding soup on a steam table drops below $135^{\circ}\mathrm{F}$ ($57^{\circ}\mathrm{C}$) after $2\ \text{hours}$, reheat to the correct temp or discard).

• Important tool: thermometer (discussed in depth below).

Thermometers and Temperature Monitoring

• Types of thermometers commonly used:

  • Bimetallic stem thermometers (BST)

  • Thermocouples

  • Thermistors

• Key distinction: thermocouples and thermistors measure temperature via a probe and typically display temperatures digitally; BST shows temperatures on a dial.

• BST specifics:

  • Range: $0^{\circ}\mathrm{F} \le T \le 220^{\circ}\mathrm{F}$; $-18^{\circ}\mathrm{C} \le T \le 104^{\circ}\mathrm{C}$

  • Indicator head, calibration nut, and metal stem with a dimple indicating the end of sensing area starts at the tip.

  • The dimple marks where the sensing area begins; reading is taken from the sensing area to the tip; useful for large or thick foods.

• Thermocouples and thermistors:

  • Probes may be permanently attached or removable; display is digital.

  • Temperature sensing area is at the tip of the probe; insert only the tip for accurate readings; suitable for both thick and thin foods.

• Probes and their uses:

  • Penetration probe: best for internal temp of meat, fish, poultry; sharp tips for thin or small pieces; e.g., ground beef patty.

  • Immersion probe: best for liquids (soups, sauces, frying oil).

  • Surface probe: best for surface temp of flat cooking equipment (e.g., griddle).

  • Air (or penetration in cold space) probe: best for checking the inside air temperature of a cooler or oven.

  • Ground beef patty example: use penetration probe.

  • Large stockpot of soup example: use immersion probe.

  • Griddle surface temp example: use surface probe.

  • Inside cooler example: use air probe.

• Infrared thermometers:

  • Measure surface temperature without touching; good for surfaces and foods, reducing cross contamination risk.

  • Cannot measure internal temperature or air temperature.

  • Use by holding as close as possible to the surface without touching; remove obstacles; do not read through metal or glass; follow manufacturer instructions for accuracy.

• Other monitoring tools:

  • Maximum registering thermometer: records the highest temperature reached during use (e.g., final rinse temp in a dishwasher).

  • Time-temperature indicator (TTI): used mainly by suppliers; color-changing windows indicate temperature abuse during shipment or storage; non-reversible color change.

  • Temperature recording devices: sometimes placed on delivery trucks or food packaging; check devices during receiving to verify safe shipping temperatures.

Using and Caring for Thermometers

• Always follow manufacturer directions for use and care.

• Cleaning and sanitizing:

  • Thermometers must be washed, rinsed, sanitized, and air dried before and after use to prevent cross contamination.

  • Storage cases should be kept clean.

  • Sanitizing solution used must be appropriate for food-contact surfaces.

  • Maintain plenty of clean, sanitized thermometers on hand.

• Calibration and accuracy:

  • Thermometers can lose accuracy and may need calibration or replacement.

  • Calibrate after bump or drop, after exposure to extreme temperatures, before each shift, and before deliveries.

  • Some thermometers cannot be calibrated and must be replaced; others can be calibrated by the user or sent to the manufacturer.

• Calibration methods:

  • Ice point method (freezing water): prepare a container with ice and water, submerge the sensing area, wait up to $30\ \text{s}$ for stabilization, and adjust to $32^{\circ}\mathrm{F}$ ($0^{\circ}\mathrm{C}$).

  • BST calibration: adjust by turning the calibration nut on the head with a wrench or tool.

  • Thermocouple/Thermistor: follow manufacturer directions for adjustment.

  • Boiling point method: adjust to the boiling temperature of water at your elevation (usually $212^{\circ}\mathrm{F}$, $100^{\circ}\mathrm{C}$ at sea level; adjust for elevation).

• Calibration timing and maintenance:

  • Calibrate after bumps/drops, before shifts, and before deliveries.

  • Some thermometers can be calibrated; others may require replacement or professional service.

• Accuracy standards:

  • For food-contact measurements: accuracy within

  • $\pm 2^{\circ}\mathrm{F} \quad \text{or} \quad \pm 1^{\circ}\mathrm{C}$

  • For air temperature in storage equipment: $\pm 3^{\circ}\mathrm{F} \quad \text{or} \quad \pm 1.5^{\circ}\mathrm{C}$

• Reading guidance:

  • Insert the probe into the thickest part of the food (center is typical).

  • Take readings at multiple spots because temperatures can vary within a large item.

  • Wait for the reading to steady before recording.

  • BST readings take longer (digital displays are common with thermocouples/thermistors but not always with BST).

• Special cautions:

  • Glass thermometers (e.g., candy thermometers) can become a physical contaminant if they break; use only if enclosed in a shatterproof casing.

  • When checking food, always insert into the thickest part of the food for accuracy.

Quick Review / Practice Questions

• Which practice can help prevent cross contamination?

  • Separating raw and ready-to-eat foods and using color-coded equipment helps.

• How long can food remain in the TDZ before disposal?

  • If held in the TDZ for $4 \text{ hours}$, discard it.

• How far must you insert a BST to get an accurate reading?

  • Insert from the tip of the stem to the dimple; sensing area begins at the tip up to the dimple.

• Which probe should be used for chicken breast temperature?

  • Penetration probe (meat, fish, poultry internal temperatures).

• Which thermometer measures surface temperature only?

  • Infrared thermometer.

• Which device is best for measuring the final rinse temperature in a dishwasher?

  • Maximum registering thermometer.

• Where should the thermometer stem/probe be placed when checking food?

  • Insert into the thickest part of the food.

First Steps in the Flow of Food (Overview of the Module)

• The first few steps in the flow of food discussed include purchasing, receiving, and storage.

• A reminder that a lot can happen to food as it moves through the operation; risks include thawing, improper storage, and improper cooking temperatures.

• The module emphasizes understanding and implementing controls to keep food safe during all stages of the flow of food.

• Final note from the transcript mentions module five and tomorrow’s session; keep in mind this content builds toward upcoming modules.

Connections to Foundational Principles and Real-World Relevance

• The flow of food connects to foundational HACCP-like principles: ensuring safety at each step to prevent HACCP hazards.

• Practical relevance: using color-coded tools, proper thermometers, and documented procedures reduces risk and supports regulatory compliance.

• Ethical implications: professionals have a duty to protect consumers from foodborne illness by applying these controls consistently.

Mathematical and Quantitative Details (Summary of Key Numbers)

• TDZ ranges:

  • $41^{\circ}\mathrm{F} \le T \le 135^{\circ}\mathrm{F}$ ⇔ $5^{\circ}\mathrm{C} \le T \le 57^{\circ}\mathrm{C}$

• Faster growth range:

  • $70^{\circ}\mathrm{F} \le T \le 125^{\circ}\mathrm{F}$ ⇔ $21^{\circ}\mathrm{C} \le T \le 52^{\circ}\mathrm{C}$

• Four-hour rule: $4\ \text{hours}$ in TDZ requires disposal.

• Calibration temperatures:

  • Ice point: $32^{\circ}\mathrm{F} = 0^{\circ}\mathrm{C}$

  • Boiling point: $212^{\circ}\mathrm{F} = 100^{\circ}\mathrm{C}$ (adjust for elevation as needed)

• Accuracy requirements:

  • Food measurements: $\pm 2^{\circ}\mathrm{F} \text{ or } \pm 1^{\circ}\mathrm{C}$

  • Air in storage equipment: $\pm 3^{\circ}\mathrm{F} \text{ or } \pm 1.5^{\circ}\mathrm{C}$

• Reading times:

  • Ice point stabilization: up to $30\ \text{s}$

  • BST reading time: vs. faster digital readouts (approximate depending on model)

End of Notes