SOP: Test for Thermal Shock Resistance of Glass Containers

GIFSQ — Global Institute for Food Safety & Quality

Principle

Thermal shock resistance is measured as the difference between the upper temperature (T₁) of the hot bath in which the containers are heated and the lower temperature (T₂) of the cold water bath into which they are transferred. The containers are examined for cracks or damage after the sudden temperature change.

Apparatus required

• Hot water and cold water baths with thermostats (range 0–100 °C ± 1 °C) with agitation device
• Wire baskets to hold the sample bottles

Procedure

Fill the hot water and cold water baths with water

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Note the temperature of the water in the cold water bath (T₂ °C)

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Adjust the temperature of the hot water bath (T₁ °C) so that T₁ − T₂ is equal to 43 °C

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When the hot water bath has attained the desired temperature, place the wire basket containing the bottles in the bath and let the bottles get filled with water

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Allow the bottles to remain in the hot bath for 15 min + 10 seconds

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Transfer the wire basket containing the water-filled bottles to the cold water bath, completing the transfer in 10 ± 2 seconds

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Immerse the bottles completely in the cold water, taking care that no cold water enters the bottle

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Allow the bottles to remain in the cold water bath for not more than 2 min, then remove them

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Examine each bottle for any visible cracks or damage

Precautions

• Bottles used in this test must not be used for any other test or for packing of foods.
• Sampling: for testing thermal shock resistance, take 1% of the total number of bottles in the lot, subject to a minimum of one and a maximum of ten bottles. The lot may be accepted if there are no failures.
• Glass containers must be conditioned before receiving hot products and cooled carefully after filling and sealing; the temperature differential between the inner and outer surfaces of the bottles should not exceed 44.4 °C.
• By using ice-cold water, the temperature difference between the hot and cold baths can be varied up to 100 °C.

Interpretation

The sample of bottles is considered satisfactory if there are no visible cracks or damage after the test.

References

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

Methods for Thermal Shock Tests on Glassware, IS: 6506-1972.