SOP: Measurement of Product Temperature in Frozen Foods

GIFSQ — Global Institute for Food Safety & Quality

Principle

Frozen blocks often carry large temperature gradients — during or just after freezing, or after exposure to ambient air — and the maximum product temperature in storage and handling must be measured directly inside the product. A thin probe, pushed in roughly along the food’s major axes, gives the best reading in a frozen block. A standard thermometer by itself offers only an approximate average.

Apparatus required

• Thin probe-type thermometers
• Ecklund needle-type thermocouple with a potentiometer graduated in °F (for recording temperature changes during freezing)
• Glass or metal stem-type thermometers

Procedure

For recording temperature changes during freezing, use the Ecklund needle-type thermocouple with the potentiometer graduated in °F

↓

For measuring the temperature of a frozen block, insert the probe of a thin probe-type thermometer roughly along the major axes of the food

↓

If a glass or metal stem-type thermometer is used, insert the stem at least 7.5 cm inside the product and press it tightly between the packages

↓

Leave the thermometer in contact with the frozen product for 5 to 10 min before taking the reading, so that a steady accurate reading is obtained

Precautions

• Glass or metal stem-type thermometers may cause considerable errors; insert the stem at least 7.5 cm and press tightly between packages for a fairly accurate measurement.
• Do not read the thermometer before 5 to 10 min of contact, as the reading must be steady.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.