Heat Testing of PET Jar

hot steaming peanut jar

This plastic jar is polyethylene terephthalate bottle, PET. The store staff was calling it a peanut jar and that was all information he could gave me. Even the most important thing, is it sterile or not? If it is, then I can just fill it with freshly prepared peanut or anything without the need of prior disinfection. That is not the case so I have to find it out myself.

pet peanut jar

It looks clean to my naked eye. It may not need serious washing with soap and water. Sterilization is next. Perhaps it has microbes not visible with human eye. Treating it with hot water is the common and easiest method to employ. Of course a techie guy can easily make a diy UV box for a no heat sterilization trick. Assuming you are not that guy, then hot water treatment is for you.

If the supplier assures the jar is sterile upon manufacture and delivery, then, you are in luck. They are ready for the packaging line. If your product can be cold-filled, you are in more luck then. If hot filling is necessary, then you are still in a bad shape even if the packaging is properly disinfected. Ordinary PET jars deforms at temperature of 76 C and above. For persistent guys, you have to cool down the commodity below this temperature before filling. Heat-set PET has higher heat resistance of 95 C. With this, waiting time before packing is significantly shorter.

Testing. Using water kettle as source of steam. I let the water went through a running boil. Hold the opened jar with a forceps. Then place it against the rushing steam. I was surprised! I shrunk in a blink of an eye. I almost never saw how it transformed from a perfectly shaped jar to a worthless piece of trash.

hot steaming peanut jar

Water boils at 100 C, more or less, depending on its purity and place altitude. Steam temperature should be close to that value. Heat-set PET melting temperature is 95C. So it is not right to assume the PET jar on my hand is not a heat-set PET jar. I did a second test. I got a thermos with hot water. Measured the water temperature, it was 82 C. Go another PET jar and poured the water into it. It never deformed as fast as before, it still did after few seconds.


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