Thermometers, Cross-Contamination and Thawing

Selecting and Calibrating Temperature Measuring Devices

Temperature control is the foundation of active managerial control in any commercial kitchen. To manage temperatures effectively, managers must equip staff with the correct measuring tools for specific culinary tasks. A bimetallic stemmed thermometer measures temperature through a metal probe with a sensing area extending from the tip to a dimple on the stem. Because the entire sensing area from the tip to the dimple must be submerged, bimetallic stemmed thermometers are most useful for checking temperatures of thick or large foods. In contrast, thermocouples and thermistors measure temperature through a sensor located at the very tip of the probe, making them ideal for measuring both thick and thin foods.

Kitchens also rely on specialized probes and devices designed for distinct surfaces and environments. Immersion probes are used to measure the temperature of liquids such as soups, sauces, and frying oil. Surface probes measure the temperature of flat cooking equipment, such as griddles and hot plates. Penetration probes are designed to check the internal temperature of food, particularly thin items like fish fillets or hamburger patties. To monitor ambient storage, air probes measure the internal temperature inside storage equipment such as walk-in coolers, freezers, and ovens. Infrared thermometers measure the surface temperature of food and equipment without touching the surface, which reduces cross-contamination risk; however, they cannot measure the internal temperature of food and cannot take accurate readings through glass or clear plastic packaging.

Other monitoring tools provide vital operational verification. Maximum registering thermometers indicate the highest temperature reached during use and are commonly used in commercial dishwashing machines. Time-temperature indicators attached to packaging use irreversible color changes to show if food has experienced temperature abuse during transit or storage. Managers must ensure that any food temperature measuring device with a glass sensor or stem has a shatterproof coating; the Food Code’s restriction applies to food temperature measuring devices, not every glass thermometer in a food establishment.

Regulatory standards demand high instrument accuracy. Food temperature measuring devices scaled in Fahrenheit must be accurate to within plus or minus 2°F (plus or minus 1°C), whereas ambient air and water temperature measuring devices must be accurate to within plus or minus 3°F (plus or minus 1.5°C). Managers should establish procedures for staff to check and, when needed, calibrate thermometers according to the manufacturer’s instructions before use each shift and after they are dropped, bumped, or exposed to extreme temperature changes. For ice-point calibration, place the thermometer’s sensing area in a slurry of crushed ice and water without touching the container, wait for the reading to stabilize, and adjust an adjustable thermometer to 32°F (0°C). To calibrate using the boiling-point method, submerge the sensing area in boiling water and adjust the reading to 212°F (100°C) or the appropriate boiling point for the local elevation.