What Causes Glass Jars and Bottles to Break During High-Temperature Sterilization?

What Causes Glass Jars and Bottles to Break During High-Temperature Sterilization?

During everyday business interactions, it’s common for new clients — often start-up food or beverage companies with little experience in filling processes — to inquire about whether our glass bottles and jars can withstand high temperatures. These customers frequently make the mistake of subjecting freshly sterilized bottles to a water shower immediately, which often causes the glass to break. This leads them to believe that glass bottles aren’t heat-resistant, when in reality, this is a misconception.

In fact, glass bottles are generally designed to handle high temperatures. They are produced by melting glass at temperatures exceeding 1,000 degrees Celsius, followed by gradual cooling through molding, annealing, and other treatments. Glass typically only starts to soften at temperatures between 500–600 degrees Celsius, meaning it remains stable well below these points. The real vulnerability of glass isn’t high heat itself, but rather sudden changes in temperature — what we refer to as “thermal shock” or “thermal vibration” in technical terms. So, glass bottles are not inherently sensitive to heat, but rapid cooling or heating can cause them to crack or shatter.

Glass bottles are formed using both open and closed molds. The areas where stress is most heavily concentrated include the bottle’s body, its base, and the sections shaped by these molds. During rapid temperature changes — quick heating and cooling — the molecules in these regions become highly active. When this molecular activity exceeds the material’s capacity to withstand stress, it can result in physical breakage or cracking of the glass.

How to Sterilize Glass Bottles Without Causing Them to Break

Based on the analysis above, we can reach the following conclusions:

Glass exhibits excellent resistance to high temperatures; however, it is vulnerable to breakage when subjected to sudden temperature changes. To accommodate most users, manufacturers typically set a maximum allowable temperature differential of 42°C — meaning that glass containers should not experience thermal fluctuations exceeding this value. Therefore, after the filling and sterilization processes, bottles should not be immediately cooled with water showers. Instead, they should first undergo a pressure release and gradual cooling period. Only once the difference between the indicated temperature and the water temperature is within 42°C should water showers be used to further cool the bottles. This approach helps prevent the glass from shattering.

If you have any specialized questions regarding the packaging of glass jars and bottles, please feel free to contact us for prompt assistance.